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src/hotspot/share/runtime/synchronizer.cpp
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rev 57560 : imported patch 8235795.patch.cr0
rev 57561 : dholmes CR - refactor common code, refactor atomic load of LVars.population in monitors_used_above_threshold, simplify list walking in ObjectSynchronizer::om_release() so we lock fewer ObjectMonitors, remove unnecessary locking from ObjectSynchronizer::deflate_monitor_list(), add NoSafepointVerifier helpers to main list management functions, remove unnecessary storestore(), remove unnecessary comments, clarify/fix comments.
@@ -115,26 +115,277 @@
#define NINFLATIONLOCKS 256
static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
// global list of blocks of monitors
-PaddedObjectMonitor* volatile ObjectSynchronizer::g_block_list = NULL;
-// Global ObjectMonitor free list. Newly allocated and deflated
-// ObjectMonitors are prepended here.
-ObjectMonitor* volatile ObjectSynchronizer::g_free_list = NULL;
-// Global ObjectMonitor in-use list. When a JavaThread is exiting,
-// ObjectMonitors on its per-thread in-use list are prepended here.
-ObjectMonitor* volatile ObjectSynchronizer::g_om_in_use_list = NULL;
-int ObjectSynchronizer::g_om_in_use_count = 0; // # on g_om_in_use_list
-
-static volatile intptr_t gListLock = 0; // protects global monitor lists
-static volatile int g_om_free_count = 0; // # on g_free_list
-static volatile int g_om_population = 0; // # Extant -- in circulation
+PaddedObjectMonitor* ObjectSynchronizer::g_block_list = NULL;
+
+struct ListGlobals {
+ char _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
+ // These are highly shared list related variables.
+ // To avoid false-sharing they need to be the sole occupants of a cache line.
+
+ // Global ObjectMonitor free list. Newly allocated and deflated
+ // ObjectMonitors are prepended here.
+ ObjectMonitor* free_list;
+ DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
+
+ // Global ObjectMonitor in-use list. When a JavaThread is exiting,
+ // ObjectMonitors on its per-thread in-use list are prepended here.
+ ObjectMonitor* in_use_list;
+ DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
+
+ int free_count; // # on free_list
+ DEFINE_PAD_MINUS_SIZE(3, DEFAULT_CACHE_LINE_SIZE, sizeof(int));
+
+ int in_use_count; // # on in_use_list
+ DEFINE_PAD_MINUS_SIZE(4, DEFAULT_CACHE_LINE_SIZE, sizeof(int));
+
+ int population; // # Extant -- in circulation
+ DEFINE_PAD_MINUS_SIZE(5, DEFAULT_CACHE_LINE_SIZE, sizeof(int));
+};
+static ListGlobals LVars;
#define CHAINMARKER (cast_to_oop<intptr_t>(-1))
+// =====================> Spin-lock functions
+
+// ObjectMonitors are not lockable outside of this file. We use spin-locks
+// implemented using a bit in the _next_om field instead of the heavier
+// weight locking mechanisms for faster list management.
+
+#define OM_LOCK_BIT 0x1
+
+// Return true if the ObjectMonitor is locked.
+// Otherwise returns false.
+static bool is_locked(ObjectMonitor* om) {
+ return ((intptr_t)Atomic::load(&om->_next_om) & OM_LOCK_BIT) == OM_LOCK_BIT;
+}
+
+// Mark an ObjectMonitor* with OM_LOCK_BIT and return it.
+static ObjectMonitor* mark_om_ptr(ObjectMonitor* om) {
+ return (ObjectMonitor*)((intptr_t)om | OM_LOCK_BIT);
+}
+
+// Return the unmarked next field in an ObjectMonitor. Note: the next
+// field may or may not have been marked with OM_LOCK_BIT originally.
+static ObjectMonitor* unmarked_next(ObjectMonitor* om) {
+ return (ObjectMonitor*)((intptr_t)Atomic::load(&om->_next_om) & ~OM_LOCK_BIT);
+}
+
+// Try to lock an ObjectMonitor. Returns true if locking was successful.
+// Otherwise returns false.
+static bool try_om_lock(ObjectMonitor* om) {
+ // Get current next field without any OM_LOCK_BIT value.
+ ObjectMonitor* next = unmarked_next(om);
+ if (Atomic::cmpxchg(&om->_next_om, next, mark_om_ptr(next)) != next) {
+ return false; // Cannot lock the ObjectMonitor.
+ }
+ return true;
+}
+
+// Lock an ObjectMonitor.
+static void om_lock(ObjectMonitor* om) {
+ while (true) {
+ if (try_om_lock(om)) {
+ return;
+ }
+ }
+}
+
+// Unlock an ObjectMonitor.
+static void om_unlock(ObjectMonitor* om) {
+ ObjectMonitor* next = Atomic::load(&om->_next_om);
+ guarantee(((intptr_t)next & OM_LOCK_BIT) == OM_LOCK_BIT, "next=" INTPTR_FORMAT
+ " must have OM_LOCK_BIT=%x set.", p2i(next), OM_LOCK_BIT);
+
+ next = (ObjectMonitor*)((intptr_t)next & ~OM_LOCK_BIT); // Clear OM_LOCK_BIT.
+ Atomic::store(&om->_next_om, next);
+}
+
+// Get the list head after locking it. Returns the list head or NULL
+// if the list is empty.
+static ObjectMonitor* get_list_head_locked(ObjectMonitor** list_p) {
+ while (true) {
+ ObjectMonitor* mid = Atomic::load(list_p);
+ if (mid == NULL) {
+ return NULL; // The list is empty.
+ }
+ if (try_om_lock(mid)) {
+ if (Atomic::load(list_p) != mid) {
+ // The list head changed before we could lock it so we have to retry.
+ om_unlock(mid);
+ continue;
+ }
+ return mid;
+ }
+ }
+}
+
+#undef OM_LOCK_BIT
+
+
+// =====================> List Management functions
+
+// Set the next field in an ObjectMonitor to the specified value.
+static void set_next(ObjectMonitor* om, ObjectMonitor* value) {
+ Atomic::store(&om->_next_om, value);
+}
+
+// Prepend a list of ObjectMonitors to the specified *list_p. 'tail' is
+// the last ObjectMonitor in the list and there are 'count' on the list.
+// Also updates the specified *count_p.
+static void prepend_list_to_common(ObjectMonitor* list, ObjectMonitor* tail,
+ int count, ObjectMonitor** list_p,
+ int* count_p) {
+ while (true) {
+ ObjectMonitor* cur = Atomic::load(list_p);
+ // Prepend list to *list_p.
+ if (!try_om_lock(tail)) {
+ continue; // failed to lock tail so try it all again
+ }
+ set_next(tail, cur); // tail now points to cur (and unlocks tail)
+ if (cur == NULL) {
+ // No potential race with takers or other prependers since
+ // *list_p is empty.
+ if (Atomic::cmpxchg(list_p, cur, list) == cur) {
+ // Successfully switched *list_p to the list value.
+ Atomic::add(count_p, count);
+ break;
+ }
+ // Implied else: try it all again
+ } else {
+ if (!try_om_lock(cur)) {
+ continue; // failed to lock cur so try it all again
+ }
+ // We locked cur so try to switch *list_p to the list value.
+ if (Atomic::cmpxchg(list_p, cur, list) != cur) {
+ // The list head has changed so unlock cur and try again:
+ om_unlock(cur);
+ continue;
+ }
+ Atomic::add(count_p, count);
+ om_unlock(cur);
+ break;
+ }
+ }
+}
+
+// Prepend a newly allocated block of ObjectMonitors to g_block_list and
+// LVars.free_list. Also updates LVars.population and LVars.free_count.
+void ObjectSynchronizer::prepend_block_to_lists(PaddedObjectMonitor* new_blk) {
+ // First we handle g_block_list:
+ while (true) {
+ PaddedObjectMonitor* cur = Atomic::load(&g_block_list);
+ // Prepend new_blk to g_block_list. The first ObjectMonitor in
+ // a block is reserved for use as linkage to the next block.
+ Atomic::store(&new_blk[0]._next_om, cur);
+ if (Atomic::cmpxchg(&g_block_list, cur, new_blk) == cur) {
+ // Successfully switched g_block_list to the new_blk value.
+ Atomic::add(&LVars.population, _BLOCKSIZE - 1);
+ break;
+ }
+ // Implied else: try it all again
+ }
+
+ // Second we handle LVars.free_list:
+ prepend_list_to_common(new_blk + 1, &new_blk[_BLOCKSIZE - 1], _BLOCKSIZE - 1,
+ &LVars.free_list, &LVars.free_count);
+}
+
+// Prepend a list of ObjectMonitors to LVars.free_list. 'tail' is the last
+// ObjectMonitor in the list and there are 'count' on the list. Also
+// updates LVars.free_count.
+static void prepend_list_to_global_free_list(ObjectMonitor* list,
+ ObjectMonitor* tail, int count) {
+ prepend_list_to_common(list, tail, count, &LVars.free_list, &LVars.free_count);
+}
+
+// Prepend a list of ObjectMonitors to LVars.in_use_list. 'tail' is the last
+// ObjectMonitor in the list and there are 'count' on the list. Also
+// updates LVars.in_use_list.
+static void prepend_list_to_global_in_use_list(ObjectMonitor* list,
+ ObjectMonitor* tail, int count) {
+ prepend_list_to_common(list, tail, count, &LVars.in_use_list, &LVars.in_use_count);
+}
+
+// Prepend an ObjectMonitor to the specified list. Also updates
+// the specified counter.
+static void prepend_to_common(ObjectMonitor* m, ObjectMonitor** list_p,
+ int* count_p) {
+ while (true) {
+ om_lock(m); // Lock m so we can safely update its next field.
+ ObjectMonitor* cur = NULL;
+ // Lock the list head to guard against races with a list walker
+ // thread:
+ if ((cur = get_list_head_locked(list_p)) != NULL) {
+ // List head is now locked so we can safely switch it.
+ set_next(m, cur); // m now points to cur (and unlocks m)
+ Atomic::store(list_p, m); // Switch list head to unlocked m.
+ om_unlock(cur);
+ break;
+ }
+ // The list is empty so try to set the list head.
+ assert(cur == NULL, "cur must be NULL: cur=" INTPTR_FORMAT, p2i(cur));
+ set_next(m, cur); // m now points to NULL (and unlocks m)
+ if (Atomic::cmpxchg(list_p, cur, m) == cur) {
+ // List head is now unlocked m.
+ break;
+ }
+ // Implied else: try it all again
+ }
+ Atomic::inc(count_p);
+}
+
+// Prepend an ObjectMonitor to a per-thread om_free_list.
+// Also updates the per-thread om_free_count.
+static void prepend_to_om_free_list(Thread* self, ObjectMonitor* m) {
+ prepend_to_common(m, &self->om_free_list, &self->om_free_count);
+}
+
+// Prepend an ObjectMonitor to a per-thread om_in_use_list.
+// Also updates the per-thread om_in_use_count.
+static void prepend_to_om_in_use_list(Thread* self, ObjectMonitor* m) {
+ prepend_to_common(m, &self->om_in_use_list, &self->om_in_use_count);
+}
+
+// Take an ObjectMonitor from the start of the specified list. Also
+// decrements the specified counter. Returns NULL if none are available.
+static ObjectMonitor* take_from_start_of_common(ObjectMonitor** list_p,
+ int* count_p) {
+ ObjectMonitor* take = NULL;
+ // Lock the list head to guard against races with a list walker
+ // thread:
+ if ((take = get_list_head_locked(list_p)) == NULL) {
+ return NULL; // None are available.
+ }
+ ObjectMonitor* next = unmarked_next(take);
+ // Switch locked list head to next (which unlocks the list head, but
+ // leaves take locked):
+ Atomic::store(list_p, next);
+ Atomic::dec(count_p);
+ // Unlock take, but leave the next value for any lagging list
+ // walkers. It will get cleaned up when take is prepended to
+ // the in-use list:
+ om_unlock(take);
+ return take;
+}
+
+// Take an ObjectMonitor from the start of the LVars.free_list. Also
+// updates LVars.free_count. Returns NULL if none are available.
+static ObjectMonitor* take_from_start_of_global_free_list() {
+ return take_from_start_of_common(&LVars.free_list, &LVars.free_count);
+}
+
+// Take an ObjectMonitor from the start of a per-thread free-list.
+// Also updates om_free_count. Returns NULL if none are available.
+static ObjectMonitor* take_from_start_of_om_free_list(Thread* self) {
+ return take_from_start_of_common(&self->om_free_list, &self->om_free_count);
+}
+
+
// =====================> Quick functions
// The quick_* forms are special fast-path variants used to improve
// performance. In the simplest case, a "quick_*" implementation could
// simply return false, in which case the caller will perform the necessary
@@ -886,40 +1137,52 @@
}
// Visitors ...
void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
- PaddedObjectMonitor* block = Atomic::load_acquire(&g_block_list);
+ PaddedObjectMonitor* block = Atomic::load(&g_block_list);
while (block != NULL) {
assert(block->object() == CHAINMARKER, "must be a block header");
for (int i = _BLOCKSIZE - 1; i > 0; i--) {
ObjectMonitor* mid = (ObjectMonitor *)(block + i);
oop object = (oop)mid->object();
if (object != NULL) {
// Only process with closure if the object is set.
closure->do_monitor(mid);
}
}
- block = (PaddedObjectMonitor*)block->_next_om;
+ // unmarked_next() is not needed with g_block_list (no locking
+ // used with block linkage _next_om fields).
+ block = (PaddedObjectMonitor*)Atomic::load(&block->_next_om);
}
}
static bool monitors_used_above_threshold() {
- if (g_om_population == 0) {
+ int population = Atomic::load(&LVars.population);
+ if (population == 0) {
return false;
}
- int monitors_used = g_om_population - g_om_free_count;
- int monitor_usage = (monitors_used * 100LL) / g_om_population;
+ if (MonitorUsedDeflationThreshold > 0) {
+ int monitors_used = population - Atomic::load(&LVars.free_count);
+ int monitor_usage = (monitors_used * 100LL) / population;
return monitor_usage > MonitorUsedDeflationThreshold;
+ }
+ return false;
+}
+
+// Returns true if MonitorBound is set (> 0) and if the specified
+// cnt is > MonitorBound. Otherwise returns false.
+static bool is_MonitorBound_exceeded(const int cnt) {
+ const int mx = MonitorBound;
+ return mx > 0 && cnt > mx;
}
bool ObjectSynchronizer::is_cleanup_needed() {
- if (MonitorUsedDeflationThreshold > 0) {
if (monitors_used_above_threshold()) {
+ // Too many monitors in use.
return true;
}
- }
return needs_monitor_scavenge();
}
bool ObjectSynchronizer::needs_monitor_scavenge() {
if (Atomic::load(&_forceMonitorScavenge) == 1) {
@@ -935,47 +1198,45 @@
global_used_oops_do(f);
}
void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
- list_oops_do(g_om_in_use_list, f);
+ list_oops_do(Atomic::load(&LVars.in_use_list), f);
}
void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
list_oops_do(thread->om_in_use_list, f);
}
void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
- ObjectMonitor* mid;
- for (mid = list; mid != NULL; mid = mid->_next_om) {
+ // The oops_do() phase does not overlap with monitor deflation
+ // so no need to lock ObjectMonitors for the list traversal.
+ for (ObjectMonitor* mid = list; mid != NULL; mid = unmarked_next(mid)) {
if (mid->object() != NULL) {
f->do_oop((oop*)mid->object_addr());
}
}
}
// -----------------------------------------------------------------------------
// ObjectMonitor Lifecycle
// -----------------------
-// Inflation unlinks monitors from the global g_free_list and
-// associates them with objects. Deflation -- which occurs at
-// STW-time -- disassociates idle monitors from objects. Such
-// scavenged monitors are returned to the g_free_list.
-//
-// The global list is protected by gListLock. All the critical sections
-// are short and operate in constant-time.
+// Inflation unlinks monitors from LVars.free_list or a per-thread free
+// list and associates them with objects. Deflation -- which occurs at
+// STW-time -- disassociates idle monitors from objects.
+// Such scavenged monitors are returned to the LVars.free_list.
//
// ObjectMonitors reside in type-stable memory (TSM) and are immortal.
//
// Lifecycle:
-// -- unassigned and on the global free list
-// -- unassigned and on a thread's private om_free_list
+// -- unassigned and on the LVars.free_list
+// -- unassigned and on a per-thread free list
// -- assigned to an object. The object is inflated and the mark refers
-// to the objectmonitor.
+// to the ObjectMonitor.
// Constraining monitor pool growth via MonitorBound ...
//
// If MonitorBound is not set (<= 0), MonitorBound checks are disabled.
@@ -991,11 +1252,11 @@
// we could just loop. In addition, if MonitorBound is set to a low value
// we'll incur more safepoints, which are harmful to performance.
// See also: GuaranteedSafepointInterval
//
// If MonitorBound is set, the boundry applies to
-// (g_om_population - g_om_free_count)
+// (LVars.population - LVars.free_count)
// i.e., if there are not enough ObjectMonitors on the global free list,
// then a safepoint deflation is induced. Picking a good MonitorBound value
// is non-trivial.
static void InduceScavenge(Thread* self, const char * Whence) {
@@ -1003,11 +1264,11 @@
// Ultimately, this results in a call to deflate_idle_monitors() in the near future.
// More precisely, trigger a cleanup safepoint as the number
// of active monitors passes the specified threshold.
// TODO: assert thread state is reasonable
- if (Atomic::xchg (&_forceMonitorScavenge, 1) == 0) {
+ if (Atomic::xchg(&_forceMonitorScavenge, 1) == 0) {
VMThread::check_for_forced_cleanup();
}
}
ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self) {
@@ -1015,55 +1276,51 @@
// and list coherency traffic, but also tends to increase the
// number of ObjectMonitors in circulation as well as the STW
// scavenge costs. As usual, we lean toward time in space-time
// tradeoffs.
const int MAXPRIVATE = 1024;
+ NoSafepointVerifier nsv;
+
stringStream ss;
for (;;) {
ObjectMonitor* m;
// 1: try to allocate from the thread's local om_free_list.
// Threads will attempt to allocate first from their local list, then
- // from the global list, and only after those attempts fail will the thread
- // attempt to instantiate new monitors. Thread-local free lists take
- // heat off the gListLock and improve allocation latency, as well as reducing
- // coherency traffic on the shared global list.
- m = self->om_free_list;
+ // from the global list, and only after those attempts fail will the
+ // thread attempt to instantiate new monitors. Thread-local free lists
+ // improve allocation latency, as well as reducing coherency traffic
+ // on the shared global list.
+ m = take_from_start_of_om_free_list(self);
if (m != NULL) {
- self->om_free_list = m->_next_om;
- self->om_free_count--;
guarantee(m->object() == NULL, "invariant");
- m->_next_om = self->om_in_use_list;
- self->om_in_use_list = m;
- self->om_in_use_count++;
+ prepend_to_om_in_use_list(self, m);
return m;
}
- // 2: try to allocate from the global g_free_list
+ // 2: try to allocate from the global LVars.free_list
// CONSIDER: use muxTry() instead of muxAcquire().
// If the muxTry() fails then drop immediately into case 3.
// If we're using thread-local free lists then try
// to reprovision the caller's free list.
- if (g_free_list != NULL) {
+ if (Atomic::load(&LVars.free_list) != NULL) {
// Reprovision the thread's om_free_list.
// Use bulk transfers to reduce the allocation rate and heat
// on various locks.
- Thread::muxAcquire(&gListLock, "om_alloc(1)");
- for (int i = self->om_free_provision; --i >= 0 && g_free_list != NULL;) {
- g_om_free_count--;
- ObjectMonitor* take = g_free_list;
- g_free_list = take->_next_om;
+ for (int i = self->om_free_provision; --i >= 0;) {
+ ObjectMonitor* take = take_from_start_of_global_free_list();
+ if (take == NULL) {
+ break; // No more are available.
+ }
guarantee(take->object() == NULL, "invariant");
take->Recycle();
om_release(self, take, false);
}
- Thread::muxRelease(&gListLock);
- self->om_free_provision += 1 + (self->om_free_provision/2);
+ self->om_free_provision += 1 + (self->om_free_provision / 2);
if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE;
- const int mx = MonitorBound;
- if (mx > 0 && (g_om_population-g_om_free_count) > mx) {
+ if (is_MonitorBound_exceeded(Atomic::load(&LVars.population) - Atomic::load(&LVars.free_count))) {
// Not enough ObjectMonitors on the global free list.
// We can't safely induce a STW safepoint from om_alloc() as our thread
// state may not be appropriate for such activities and callers may hold
// naked oops, so instead we defer the action.
InduceScavenge(self, "om_alloc");
@@ -1094,41 +1351,24 @@
// The trick of using the 1st element in the block as g_block_list
// linkage should be reconsidered. A better implementation would
// look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
for (int i = 1; i < _BLOCKSIZE; i++) {
- temp[i]._next_om = (ObjectMonitor *)&temp[i+1];
+ Atomic::store(&temp[i]._next_om, (ObjectMonitor*)&temp[i + 1]);
}
// terminate the last monitor as the end of list
- temp[_BLOCKSIZE - 1]._next_om = NULL;
+ Atomic::store(&temp[_BLOCKSIZE - 1]._next_om, (ObjectMonitor*)NULL);
// Element [0] is reserved for global list linkage
temp[0].set_object(CHAINMARKER);
// Consider carving out this thread's current request from the
// block in hand. This avoids some lock traffic and redundant
// list activity.
- // Acquire the gListLock to manipulate g_block_list and g_free_list.
- // An Oyama-Taura-Yonezawa scheme might be more efficient.
- Thread::muxAcquire(&gListLock, "om_alloc(2)");
- g_om_population += _BLOCKSIZE-1;
- g_om_free_count += _BLOCKSIZE-1;
-
- // Add the new block to the list of extant blocks (g_block_list).
- // The very first ObjectMonitor in a block is reserved and dedicated.
- // It serves as blocklist "next" linkage.
- temp[0]._next_om = g_block_list;
- // There are lock-free uses of g_block_list so make sure that
- // the previous stores happen before we update g_block_list.
- Atomic::release_store(&g_block_list, temp);
-
- // Add the new string of ObjectMonitors to the global free list
- temp[_BLOCKSIZE - 1]._next_om = g_free_list;
- g_free_list = temp + 1;
- Thread::muxRelease(&gListLock);
+ prepend_block_to_lists(temp);
}
}
// Place "m" on the caller's private per-thread om_free_list.
// In practice there's no need to clamp or limit the number of
@@ -1144,39 +1384,91 @@
void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m,
bool from_per_thread_alloc) {
guarantee(m->header().value() == 0, "invariant");
guarantee(m->object() == NULL, "invariant");
+ NoSafepointVerifier nsv;
+
stringStream ss;
guarantee((m->is_busy() | m->_recursions) == 0, "freeing in-use monitor: "
"%s, recursions=" INTX_FORMAT, m->is_busy_to_string(&ss),
m->_recursions);
// _next_om is used for both per-thread in-use and free lists so
// we have to remove 'm' from the in-use list first (as needed).
if (from_per_thread_alloc) {
// Need to remove 'm' from om_in_use_list.
- ObjectMonitor* cur_mid_in_use = NULL;
- bool extracted = false;
- for (ObjectMonitor* mid = self->om_in_use_list; mid != NULL; cur_mid_in_use = mid, mid = mid->_next_om) {
- if (m == mid) {
- // extract from per-thread in-use list
- if (mid == self->om_in_use_list) {
- self->om_in_use_list = mid->_next_om;
- } else if (cur_mid_in_use != NULL) {
- cur_mid_in_use->_next_om = mid->_next_om; // maintain the current thread in-use list
+ ObjectMonitor* mid = NULL;
+ ObjectMonitor* next = NULL;
+
+ // This list walk can only race with another list walker since
+ // deflation can only happen at a safepoint so we don't have to
+ // worry about an ObjectMonitor being removed from this list
+ // while we are walking it.
+
+ // Lock the list head to avoid racing with another list walker.
+ if ((mid = get_list_head_locked(&self->om_in_use_list)) == NULL) {
+ fatal("thread=" INTPTR_FORMAT " in-use list must not be empty.", p2i(self));
}
- extracted = true;
- self->om_in_use_count--;
+ next = unmarked_next(mid);
+ if (m == mid) {
+ // First special case:
+ // 'm' matches mid, is the list head and is locked. Switch the list
+ // head to next which unlocks the list head, but leaves the extracted
+ // mid locked:
+ Atomic::store(&self->om_in_use_list, next);
+ } else if (m == next) {
+ // Second special case:
+ // 'm' matches next after the list head and we already have the list
+ // head locked so set mid to what we are extracting:
+ mid = next;
+ // Lock mid to prevent races with a list walker:
+ om_lock(mid);
+ // Update next to what follows mid (if anything):
+ next = unmarked_next(mid);
+ // Switch next after the list head to new next which unlocks the
+ // list head, but leaves the extracted mid locked:
+ set_next(self->om_in_use_list, next);
+ } else {
+ // We have to search the list to find 'm'.
+ om_unlock(mid); // unlock the list head
+ guarantee(next != NULL, "thread=" INTPTR_FORMAT ": om_in_use_list=" INTPTR_FORMAT
+ " is too short.", p2i(self), p2i(self->om_in_use_list));
+ // Our starting anchor is next after the list head which is the
+ // last ObjectMonitor we checked:
+ ObjectMonitor* anchor = next;
+ while ((mid = unmarked_next(anchor)) != NULL) {
+ if (m == mid) {
+ // We found 'm' on the per-thread in-use list so extract it.
+ om_lock(anchor); // Lock the anchor so we can safely modify it.
+ // Update next to what follows mid (if anything):
+ next = unmarked_next(mid);
+ // Switch next after the anchor to new next which unlocks the
+ // anchor, but leaves the extracted mid locked:
+ set_next(anchor, next);
break;
+ } else {
+ anchor = mid;
+ }
}
}
- assert(extracted, "Should have extracted from in-use list");
+
+ if (mid == NULL) {
+ // Reached end of the list and didn't find 'm' so:
+ fatal("thread=" INTPTR_FORMAT " must find m=" INTPTR_FORMAT "on om_in_use_list="
+ INTPTR_FORMAT, p2i(self), p2i(m), p2i(self->om_in_use_list));
}
- m->_next_om = self->om_free_list;
- self->om_free_list = m;
- self->om_free_count++;
+ // At this point mid is disconnected from the in-use list so
+ // its lock no longer has any effects on the in-use list.
+ Atomic::dec(&self->om_in_use_count);
+ // Unlock mid, but leave the next value for any lagging list
+ // walkers. It will get cleaned up when mid is prepended to
+ // the thread's free list:
+ om_unlock(mid);
+ }
+
+ prepend_to_om_free_list(self, m);
}
// Return ObjectMonitors on a moribund thread's free and in-use
// lists to the appropriate global lists. The ObjectMonitors on the
// per-thread in-use list may still be in use by other threads.
@@ -1189,64 +1481,101 @@
// scanned by a GC safepoint, either via Thread::oops_do() (before
// om_flush() is called) or via ObjectSynchronizer::oops_do() (after
// om_flush() is called).
void ObjectSynchronizer::om_flush(Thread* self) {
- ObjectMonitor* free_list = self->om_free_list;
- ObjectMonitor* free_tail = NULL;
- int free_count = 0;
- if (free_list != NULL) {
- ObjectMonitor* s;
- // The thread is going away. Set 'free_tail' to the last per-thread free
- // monitor which will be linked to g_free_list below under the gListLock.
- stringStream ss;
- for (s = free_list; s != NULL; s = s->_next_om) {
- free_count++;
- free_tail = s;
- guarantee(s->object() == NULL, "invariant");
- guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss));
- }
- guarantee(free_tail != NULL, "invariant");
- assert(self->om_free_count == free_count, "free-count off");
- self->om_free_list = NULL;
- self->om_free_count = 0;
- }
-
- ObjectMonitor* in_use_list = self->om_in_use_list;
- ObjectMonitor* in_use_tail = NULL;
+ // Process the per-thread in-use list first to be consistent.
int in_use_count = 0;
- if (in_use_list != NULL) {
+ ObjectMonitor* in_use_list = NULL;
+ ObjectMonitor* in_use_tail = NULL;
+ NoSafepointVerifier nsv;
+
+ // This function can race with a list walker thread so we lock the
+ // list head to prevent confusion.
+ if ((in_use_list = get_list_head_locked(&self->om_in_use_list)) != NULL) {
+ // At this point, we have locked the in-use list head so a racing
+ // thread cannot come in after us. However, a racing thread could
+ // be ahead of us; we'll detect that and delay to let it finish.
+ //
// The thread is going away, however the ObjectMonitors on the
// om_in_use_list may still be in-use by other threads. Link
// them to in_use_tail, which will be linked into the global
- // in-use list g_om_in_use_list below, under the gListLock.
- ObjectMonitor *cur_om;
- for (cur_om = in_use_list; cur_om != NULL; cur_om = cur_om->_next_om) {
+ // in-use list (LVars.in_use_list) below.
+ //
+ // Account for the in-use list head before the loop since it is
+ // already locked (by this thread):
+ in_use_tail = in_use_list;
+ in_use_count++;
+ for (ObjectMonitor* cur_om = unmarked_next(in_use_list); cur_om != NULL; cur_om = unmarked_next(cur_om)) {
+ if (is_locked(cur_om)) {
+ // cur_om is locked so there must be a racing walker thread ahead
+ // of us so we'll give it a chance to finish.
+ while (is_locked(cur_om)) {
+ os::naked_short_sleep(1);
+ }
+ }
in_use_tail = cur_om;
in_use_count++;
}
guarantee(in_use_tail != NULL, "invariant");
- assert(self->om_in_use_count == in_use_count, "in-use count off");
- self->om_in_use_list = NULL;
- self->om_in_use_count = 0;
+ int l_om_in_use_count = Atomic::load(&self->om_in_use_count);
+ assert(l_om_in_use_count == in_use_count, "in-use counts don't match: "
+ "l_om_in_use_count=%d, in_use_count=%d", l_om_in_use_count, in_use_count);
+ Atomic::store(&self->om_in_use_count, 0);
+ // Clear the in-use list head (which also unlocks it):
+ Atomic::store(&self->om_in_use_list, (ObjectMonitor*)NULL);
+ om_unlock(in_use_list);
+ }
+
+ int free_count = 0;
+ ObjectMonitor* free_list = NULL;
+ ObjectMonitor* free_tail = NULL;
+ // This function can race with a list walker thread so we lock the
+ // list head to prevent confusion.
+ if ((free_list = get_list_head_locked(&self->om_free_list)) != NULL) {
+ // At this point, we have locked the free list head so a racing
+ // thread cannot come in after us. However, a racing thread could
+ // be ahead of us; we'll detect that and delay to let it finish.
+ //
+ // The thread is going away. Set 'free_tail' to the last per-thread free
+ // monitor which will be linked to LVars.free_list below.
+ //
+ // Account for the free list head before the loop since it is
+ // already locked (by this thread):
+ free_tail = free_list;
+ free_count++;
+ for (ObjectMonitor* s = unmarked_next(free_list); s != NULL; s = unmarked_next(s)) {
+ if (is_locked(s)) {
+ // s is locked so there must be a racing walker thread ahead
+ // of us so we'll give it a chance to finish.
+ while (is_locked(s)) {
+ os::naked_short_sleep(1);
+ }
+ }
+ free_tail = s;
+ free_count++;
+ guarantee(s->object() == NULL, "invariant");
+ stringStream ss;
+ guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss));
+ }
+ guarantee(free_tail != NULL, "invariant");
+ int l_om_free_count = Atomic::load(&self->om_free_count);
+ assert(l_om_free_count == free_count, "free counts don't match: "
+ "l_om_free_count=%d, free_count=%d", l_om_free_count, free_count);
+ Atomic::store(&self->om_free_count, 0);
+ Atomic::store(&self->om_free_list, (ObjectMonitor*)NULL);
+ om_unlock(free_list);
}
- Thread::muxAcquire(&gListLock, "om_flush");
if (free_tail != NULL) {
- free_tail->_next_om = g_free_list;
- g_free_list = free_list;
- g_om_free_count += free_count;
+ prepend_list_to_global_free_list(free_list, free_tail, free_count);
}
if (in_use_tail != NULL) {
- in_use_tail->_next_om = g_om_in_use_list;
- g_om_in_use_list = in_use_list;
- g_om_in_use_count += in_use_count;
+ prepend_list_to_global_in_use_list(in_use_list, in_use_tail, in_use_count);
}
- Thread::muxRelease(&gListLock);
-
LogStreamHandle(Debug, monitorinflation) lsh_debug;
LogStreamHandle(Info, monitorinflation) lsh_info;
LogStream* ls = NULL;
if (log_is_enabled(Debug, monitorinflation)) {
ls = &lsh_debug;
@@ -1282,12 +1611,11 @@
}
inflate(Thread::current(), obj, inflate_cause_vm_internal);
}
ObjectMonitor* ObjectSynchronizer::inflate(Thread* self,
- oop object,
- const InflateCause cause) {
+ oop object, const InflateCause cause) {
// Inflate mutates the heap ...
// Relaxing assertion for bug 6320749.
assert(Universe::verify_in_progress() ||
!SafepointSynchronize::is_at_safepoint(), "invariant");
@@ -1514,10 +1842,11 @@
", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid));
const markWord dmw = mid->header();
guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
if (mid->is_busy()) {
+ // Easy checks are first - the ObjectMonitor is busy so no deflation.
deflated = false;
} else {
// Deflate the monitor if it is no longer being used
// It's idle - scavenge and return to the global free list
// plain old deflation ...
@@ -1542,12 +1871,18 @@
if (*free_tail_p != NULL) {
// We append to the list so the caller can use mid->_next_om
// to fix the linkages in its context.
ObjectMonitor* prevtail = *free_tail_p;
// Should have been cleaned up by the caller:
- assert(prevtail->_next_om == NULL, "cleaned up deflated?");
- prevtail->_next_om = mid;
+ // Note: Should not have to lock prevtail here since we're at a
+ // safepoint and ObjectMonitors on the local free list should
+ // not be accessed in parallel.
+#ifdef ASSERT
+ ObjectMonitor* l_next_om = Atomic::load(&prevtail->_next_om);
+#endif
+ assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
+ set_next(prevtail, mid);
}
*free_tail_p = mid;
// At this point, mid->_next_om still refers to its current
// value and another ObjectMonitor's _next_om field still
// refers to this ObjectMonitor. Those linkages have to be
@@ -1555,13 +1890,12 @@
deflated = true;
}
return deflated;
}
-// Walk a given monitor list, and deflate idle monitors
-// The given list could be a per-thread list or a global list
-// Caller acquires gListLock as needed.
+// Walk a given monitor list, and deflate idle monitors.
+// The given list could be a per-thread list or a global list.
//
// In the case of parallel processing of thread local monitor lists,
// work is done by Threads::parallel_threads_do() which ensures that
// each Java thread is processed by exactly one worker thread, and
// thus avoid conflicts that would arise when worker threads would
@@ -1569,35 +1903,42 @@
//
// See also ParallelSPCleanupTask and
// SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
// Threads::parallel_java_threads_do() in thread.cpp.
int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** list_p,
+ int* count_p,
ObjectMonitor** free_head_p,
ObjectMonitor** free_tail_p) {
- ObjectMonitor* mid;
- ObjectMonitor* next;
ObjectMonitor* cur_mid_in_use = NULL;
+ ObjectMonitor* mid = NULL;
+ ObjectMonitor* next = NULL;
int deflated_count = 0;
- for (mid = *list_p; mid != NULL;) {
+ // This list walk executes at a safepoint and does not race with any
+ // other list walkers.
+
+ for (mid = Atomic::load(list_p); mid != NULL; mid = next) {
+ next = unmarked_next(mid);
oop obj = (oop) mid->object();
if (obj != NULL && deflate_monitor(mid, obj, free_head_p, free_tail_p)) {
// Deflation succeeded and already updated free_head_p and
// free_tail_p as needed. Finish the move to the local free list
// by unlinking mid from the global or per-thread in-use list.
- if (mid == *list_p) {
- *list_p = mid->_next_om;
- } else if (cur_mid_in_use != NULL) {
- cur_mid_in_use->_next_om = mid->_next_om; // maintain the current thread in-use list
+ if (cur_mid_in_use == NULL) {
+ // mid is the list head so switch the list head to next:
+ Atomic::store(list_p, next);
+ } else {
+ // Switch cur_mid_in_use's next field to next:
+ set_next(cur_mid_in_use, next);
}
- next = mid->_next_om;
- mid->_next_om = NULL; // This mid is current tail in the free_head_p list
- mid = next;
+ // At this point mid is disconnected from the in-use list.
deflated_count++;
+ Atomic::dec(count_p);
+ // mid is current tail in the free_head_p list so NULL terminate it:
+ set_next(mid, NULL);
} else {
cur_mid_in_use = mid;
- mid = mid->_next_om;
}
}
return deflated_count;
}
@@ -1619,37 +1960,33 @@
if (log_is_enabled(Info, monitorinflation)) {
timer.start();
}
- // Prevent om_flush from changing mids in Thread dtor's during deflation
- // And in case the vm thread is acquiring a lock during a safepoint
- // See e.g. 6320749
- Thread::muxAcquire(&gListLock, "deflate_idle_monitors");
-
// Note: the thread-local monitors lists get deflated in
// a separate pass. See deflate_thread_local_monitors().
- // For moribund threads, scan g_om_in_use_list
+ // For moribund threads, scan LVars.in_use_list
int deflated_count = 0;
- if (g_om_in_use_list) {
- counters->n_in_circulation += g_om_in_use_count;
- deflated_count = deflate_monitor_list((ObjectMonitor **)&g_om_in_use_list, &free_head_p, &free_tail_p);
- g_om_in_use_count -= deflated_count;
- counters->n_scavenged += deflated_count;
- counters->n_in_use += g_om_in_use_count;
+ if (Atomic::load(&LVars.in_use_list) != NULL) {
+ // Update n_in_circulation before LVars.in_use_count is updated by deflation.
+ Atomic::add(&counters->n_in_circulation, Atomic::load(&LVars.in_use_count));
+
+ deflated_count = deflate_monitor_list(&LVars.in_use_list, &LVars.in_use_count, &free_head_p, &free_tail_p);
+ Atomic::add(&counters->n_in_use, Atomic::load(&LVars.in_use_count));
}
if (free_head_p != NULL) {
// Move the deflated ObjectMonitors back to the global free list.
- guarantee(free_tail_p != NULL && counters->n_scavenged > 0, "invariant");
- assert(free_tail_p->_next_om == NULL, "invariant");
- // constant-time list splice - prepend scavenged segment to g_free_list
- free_tail_p->_next_om = g_free_list;
- g_free_list = free_head_p;
+ guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
+#ifdef ASSERT
+ ObjectMonitor* l_next_om = Atomic::load(&free_tail_p->_next_om);
+#endif
+ assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
+ prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count);
+ Atomic::add(&counters->n_scavenged, deflated_count);
}
- Thread::muxRelease(&gListLock);
timer.stop();
LogStreamHandle(Debug, monitorinflation) lsh_debug;
LogStreamHandle(Info, monitorinflation) lsh_info;
LogStream* ls = NULL;
@@ -1668,22 +2005,18 @@
// monitors. Note: if the work is split among more than one
// worker thread, then the reported time will likely be more
// than a beginning to end measurement of the phase.
log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged);
- g_om_free_count += counters->n_scavenged;
-
if (log_is_enabled(Debug, monitorinflation)) {
// exit_globals()'s call to audit_and_print_stats() is done
- // at the Info level.
+ // at the Info level and not at a safepoint.
ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
} else if (log_is_enabled(Info, monitorinflation)) {
- Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors");
- log_info(monitorinflation)("g_om_population=%d, g_om_in_use_count=%d, "
- "g_om_free_count=%d", g_om_population,
- g_om_in_use_count, g_om_free_count);
- Thread::muxRelease(&gListLock);
+ log_info(monitorinflation)("global_population=%d, global_in_use_count=%d, "
+ "global_free_count=%d", Atomic::load(&LVars.population),
+ Atomic::load(&LVars.in_use_count), Atomic::load(&LVars.free_count));
}
Atomic::store(&_forceMonitorScavenge, 0); // Reset
OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged));
@@ -1703,39 +2036,34 @@
if (log_is_enabled(Info, safepoint, cleanup) ||
log_is_enabled(Info, monitorinflation)) {
timer.start();
}
- int deflated_count = deflate_monitor_list(thread->om_in_use_list_addr(), &free_head_p, &free_tail_p);
-
- Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors");
+ // Update n_in_circulation before om_in_use_count is updated by deflation.
+ Atomic::add(&counters->n_in_circulation, Atomic::load(&thread->om_in_use_count));
- // Adjust counters
- counters->n_in_circulation += thread->om_in_use_count;
- thread->om_in_use_count -= deflated_count;
- counters->n_scavenged += deflated_count;
- counters->n_in_use += thread->om_in_use_count;
- counters->per_thread_scavenged += deflated_count;
+ int deflated_count = deflate_monitor_list(&thread->om_in_use_list, &thread->om_in_use_count, &free_head_p, &free_tail_p);
+ Atomic::add(&counters->n_in_use, Atomic::load(&thread->om_in_use_count));
if (free_head_p != NULL) {
// Move the deflated ObjectMonitors back to the global free list.
guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
- assert(free_tail_p->_next_om == NULL, "invariant");
-
- // constant-time list splice - prepend scavenged segment to g_free_list
- free_tail_p->_next_om = g_free_list;
- g_free_list = free_head_p;
+#ifdef ASSERT
+ ObjectMonitor* l_next_om = Atomic::load(&free_tail_p->_next_om);
+#endif
+ assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
+ prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count);
+ Atomic::add(&counters->n_scavenged, deflated_count);
+ Atomic::add(&counters->per_thread_scavenged, deflated_count);
}
timer.stop();
// Safepoint logging cares about cumulative per_thread_times and
// we'll capture most of the cost, but not the muxRelease() which
// should be cheap.
counters->per_thread_times += timer.seconds();
- Thread::muxRelease(&gListLock);
-
LogStreamHandle(Debug, monitorinflation) lsh_debug;
LogStreamHandle(Info, monitorinflation) lsh_info;
LogStream* ls = NULL;
if (log_is_enabled(Debug, monitorinflation)) {
ls = &lsh_debug;
@@ -1782,13 +2110,11 @@
void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
assert(THREAD == JavaThread::current(), "must be current Java thread");
NoSafepointVerifier nsv;
ReleaseJavaMonitorsClosure rjmc(THREAD);
- Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
ObjectSynchronizer::monitors_iterate(&rjmc);
- Thread::muxRelease(&gListLock);
THREAD->clear_pending_exception();
}
const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
switch (cause) {
@@ -1822,10 +2148,20 @@
u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
return (u_char*)&GVars.stw_random;
}
+// This function can be called at a safepoint or it can be called when
+// we are trying to exit the VM. When we are trying to exit the VM, the
+// list walker functions can run in parallel with the other list
+// operations so spin-locking is used for safety.
+//
+// Calls to this function can be added in various places as a debugging
+// aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
+// details logged at the Info level and 'false' for the 'on_exit'
+// parameter to have in-use monitor details logged at the Trace level.
+//
void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
LogStreamHandle(Debug, monitorinflation) lsh_debug;
LogStreamHandle(Info, monitorinflation) lsh_info;
@@ -1838,42 +2174,35 @@
} else if (log_is_enabled(Info, monitorinflation)) {
ls = &lsh_info;
}
assert(ls != NULL, "sanity check");
- if (!on_exit) {
- // Not at VM exit so grab the global list lock.
- Thread::muxAcquire(&gListLock, "audit_and_print_stats");
- }
-
// Log counts for the global and per-thread monitor lists:
int chk_om_population = log_monitor_list_counts(ls);
int error_cnt = 0;
ls->print_cr("Checking global lists:");
- // Check g_om_population:
- if (g_om_population == chk_om_population) {
- ls->print_cr("g_om_population=%d equals chk_om_population=%d",
- g_om_population, chk_om_population);
- } else {
- ls->print_cr("ERROR: g_om_population=%d is not equal to "
- "chk_om_population=%d", g_om_population,
- chk_om_population);
- error_cnt++;
+ // Check LVars.population:
+ if (Atomic::load(&LVars.population) == chk_om_population) {
+ ls->print_cr("global_population=%d equals chk_om_population=%d",
+ Atomic::load(&LVars.population), chk_om_population);
+ } else {
+ // With fine grained locks on the monitor lists, it is possible for
+ // log_monitor_list_counts() to return a value that doesn't match
+ // LVars.population. So far a higher value has been seen in testing
+ // so something is being double counted by log_monitor_list_counts().
+ ls->print_cr("WARNING: global_population=%d is not equal to "
+ "chk_om_population=%d", Atomic::load(&LVars.population), chk_om_population);
}
- // Check g_om_in_use_list and g_om_in_use_count:
+ // Check LVars.in_use_list and LVars.in_use_count:
chk_global_in_use_list_and_count(ls, &error_cnt);
- // Check g_free_list and g_om_free_count:
+ // Check LVars.free_list and LVars.free_count:
chk_global_free_list_and_count(ls, &error_cnt);
- if (!on_exit) {
- Thread::muxRelease(&gListLock);
- }
-
ls->print_cr("Checking per-thread lists:");
for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
// Check om_in_use_list and om_in_use_count:
chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
@@ -1891,11 +2220,11 @@
if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
(!on_exit && log_is_enabled(Trace, monitorinflation))) {
// When exiting this log output is at the Info level. When called
// at a safepoint, this log output is at the Trace level since
// there can be a lot of it.
- log_in_use_monitor_details(ls, on_exit);
+ log_in_use_monitor_details(ls);
}
ls->flush();
guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
@@ -1942,44 +2271,86 @@
}
*error_cnt_p = *error_cnt_p + 1;
}
}
+// Lock the next ObjectMonitor for traversal and unlock the current
+// ObjectMonitor. Returns the next ObjectMonitor if there is one.
+// Otherwise returns NULL (after unlocking the current ObjectMonitor).
+// This function is used by the various list walker functions to
+// safely walk a list without allowing an ObjectMonitor to be moved
+// to another list in the middle of a walk.
+static ObjectMonitor* lock_next_for_traversal(ObjectMonitor* cur) {
+ assert(is_locked(cur), "cur=" INTPTR_FORMAT " must be locked", p2i(cur));
+ ObjectMonitor* next = unmarked_next(cur);
+ if (next == NULL) { // Reached the end of the list.
+ om_unlock(cur);
+ return NULL;
+ }
+ om_lock(next); // Lock next before unlocking current to keep
+ om_unlock(cur); // from being by-passed by another thread.
+ return next;
+}
+
// Check the global free list and count; log the results of the checks.
void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
int *error_cnt_p) {
int chk_om_free_count = 0;
- for (ObjectMonitor* n = g_free_list; n != NULL; n = n->_next_om) {
- chk_free_entry(NULL /* jt */, n, out, error_cnt_p);
+ ObjectMonitor* cur = NULL;
+ if ((cur = get_list_head_locked(&LVars.free_list)) != NULL) {
+ // Marked the global free list head so process the list.
+ while (true) {
+ chk_free_entry(NULL /* jt */, cur, out, error_cnt_p);
chk_om_free_count++;
+
+ cur = lock_next_for_traversal(cur);
+ if (cur == NULL) {
+ break;
}
- if (g_om_free_count == chk_om_free_count) {
- out->print_cr("g_om_free_count=%d equals chk_om_free_count=%d",
- g_om_free_count, chk_om_free_count);
- } else {
- out->print_cr("ERROR: g_om_free_count=%d is not equal to "
- "chk_om_free_count=%d", g_om_free_count,
- chk_om_free_count);
- *error_cnt_p = *error_cnt_p + 1;
+ }
+ }
+ int l_free_count = Atomic::load(&LVars.free_count);
+ if (l_free_count == chk_om_free_count) {
+ out->print_cr("global_free_count=%d equals chk_om_free_count=%d",
+ l_free_count, chk_om_free_count);
+ } else {
+ // With fine grained locks on LVars.free_list, it is possible for an
+ // ObjectMonitor to be prepended to LVars.free_list after we started
+ // calculating chk_om_free_count so LVars.free_count may not
+ // match anymore.
+ out->print_cr("WARNING: global_free_count=%d is not equal to "
+ "chk_om_free_count=%d", l_free_count, chk_om_free_count);
}
}
// Check the global in-use list and count; log the results of the checks.
void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
int *error_cnt_p) {
int chk_om_in_use_count = 0;
- for (ObjectMonitor* n = g_om_in_use_list; n != NULL; n = n->_next_om) {
- chk_in_use_entry(NULL /* jt */, n, out, error_cnt_p);
+ ObjectMonitor* cur = NULL;
+ if ((cur = get_list_head_locked(&LVars.in_use_list)) != NULL) {
+ // Marked the global in-use list head so process the list.
+ while (true) {
+ chk_in_use_entry(NULL /* jt */, cur, out, error_cnt_p);
chk_om_in_use_count++;
+
+ cur = lock_next_for_traversal(cur);
+ if (cur == NULL) {
+ break;
+ }
}
- if (g_om_in_use_count == chk_om_in_use_count) {
- out->print_cr("g_om_in_use_count=%d equals chk_om_in_use_count=%d", g_om_in_use_count,
- chk_om_in_use_count);
- } else {
- out->print_cr("ERROR: g_om_in_use_count=%d is not equal to chk_om_in_use_count=%d",
- g_om_in_use_count, chk_om_in_use_count);
- *error_cnt_p = *error_cnt_p + 1;
+ }
+ int l_in_use_count = Atomic::load(&LVars.in_use_count);
+ if (l_in_use_count == chk_om_in_use_count) {
+ out->print_cr("global_in_use_count=%d equals chk_om_in_use_count=%d",
+ l_in_use_count, chk_om_in_use_count);
+ } else {
+ // With fine grained locks on the monitor lists, it is possible for
+ // an exiting JavaThread to put its in-use ObjectMonitors on the
+ // global in-use list after chk_om_in_use_count is calculated above.
+ out->print_cr("WARNING: global_in_use_count=%d is not equal to chk_om_in_use_count=%d",
+ l_in_use_count, chk_om_in_use_count);
}
}
// Check an in-use monitor entry; log any errors.
void ObjectSynchronizer::chk_in_use_entry(JavaThread* jt, ObjectMonitor* n,
@@ -2043,101 +2414,129 @@
// Check the thread's free list and count; log the results of the checks.
void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
outputStream * out,
int *error_cnt_p) {
int chk_om_free_count = 0;
- for (ObjectMonitor* n = jt->om_free_list; n != NULL; n = n->_next_om) {
- chk_free_entry(jt, n, out, error_cnt_p);
+ ObjectMonitor* cur = NULL;
+ if ((cur = get_list_head_locked(&jt->om_free_list)) != NULL) {
+ // Marked the per-thread free list head so process the list.
+ while (true) {
+ chk_free_entry(jt, cur, out, error_cnt_p);
chk_om_free_count++;
+
+ cur = lock_next_for_traversal(cur);
+ if (cur == NULL) {
+ break;
}
- if (jt->om_free_count == chk_om_free_count) {
+ }
+ }
+ int l_om_free_count = Atomic::load(&jt->om_free_count);
+ if (l_om_free_count == chk_om_free_count) {
out->print_cr("jt=" INTPTR_FORMAT ": om_free_count=%d equals "
- "chk_om_free_count=%d", p2i(jt), jt->om_free_count, chk_om_free_count);
+ "chk_om_free_count=%d", p2i(jt), l_om_free_count, chk_om_free_count);
} else {
out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_free_count=%d is not "
- "equal to chk_om_free_count=%d", p2i(jt), jt->om_free_count,
+ "equal to chk_om_free_count=%d", p2i(jt), l_om_free_count,
chk_om_free_count);
*error_cnt_p = *error_cnt_p + 1;
}
}
// Check the thread's in-use list and count; log the results of the checks.
void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
outputStream * out,
int *error_cnt_p) {
int chk_om_in_use_count = 0;
- for (ObjectMonitor* n = jt->om_in_use_list; n != NULL; n = n->_next_om) {
- chk_in_use_entry(jt, n, out, error_cnt_p);
+ ObjectMonitor* cur = NULL;
+ if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
+ // Marked the per-thread in-use list head so process the list.
+ while (true) {
+ chk_in_use_entry(jt, cur, out, error_cnt_p);
chk_om_in_use_count++;
+
+ cur = lock_next_for_traversal(cur);
+ if (cur == NULL) {
+ break;
+ }
}
- if (jt->om_in_use_count == chk_om_in_use_count) {
+ }
+ int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
+ if (l_om_in_use_count == chk_om_in_use_count) {
out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals "
- "chk_om_in_use_count=%d", p2i(jt), jt->om_in_use_count,
+ "chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
chk_om_in_use_count);
} else {
out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not "
- "equal to chk_om_in_use_count=%d", p2i(jt), jt->om_in_use_count,
+ "equal to chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
chk_om_in_use_count);
*error_cnt_p = *error_cnt_p + 1;
}
}
// Log details about ObjectMonitors on the in-use lists. The 'BHL'
// flags indicate why the entry is in-use, 'object' and 'object type'
// indicate the associated object and its type.
-void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out,
- bool on_exit) {
- if (!on_exit) {
- // Not at VM exit so grab the global list lock.
- Thread::muxAcquire(&gListLock, "log_in_use_monitor_details");
- }
-
+void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out) {
stringStream ss;
- if (g_om_in_use_count > 0) {
+ if (Atomic::load(&LVars.in_use_count) > 0) {
out->print_cr("In-use global monitor info:");
out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
out->print_cr("%18s %s %18s %18s",
"monitor", "BHL", "object", "object type");
out->print_cr("================== === ================== ==================");
- for (ObjectMonitor* n = g_om_in_use_list; n != NULL; n = n->_next_om) {
- const oop obj = (oop) n->object();
- const markWord mark = n->header();
+ ObjectMonitor* cur = NULL;
+ if ((cur = get_list_head_locked(&LVars.in_use_list)) != NULL) {
+ // Marked the global in-use list head so process the list.
+ while (true) {
+ const oop obj = (oop) cur->object();
+ const markWord mark = cur->header();
ResourceMark rm;
- out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(n),
- n->is_busy() != 0, mark.hash() != 0, n->owner() != NULL,
+ out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(cur),
+ cur->is_busy() != 0, mark.hash() != 0, cur->owner() != NULL,
p2i(obj), obj->klass()->external_name());
- if (n->is_busy() != 0) {
- out->print(" (%s)", n->is_busy_to_string(&ss));
+ if (cur->is_busy() != 0) {
+ out->print(" (%s)", cur->is_busy_to_string(&ss));
ss.reset();
}
out->cr();
+
+ cur = lock_next_for_traversal(cur);
+ if (cur == NULL) {
+ break;
+ }
}
}
-
- if (!on_exit) {
- Thread::muxRelease(&gListLock);
}
out->print_cr("In-use per-thread monitor info:");
out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
out->print_cr("%18s %18s %s %18s %18s",
"jt", "monitor", "BHL", "object", "object type");
out->print_cr("================== ================== === ================== ==================");
for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
- for (ObjectMonitor* n = jt->om_in_use_list; n != NULL; n = n->_next_om) {
- const oop obj = (oop) n->object();
- const markWord mark = n->header();
+ ObjectMonitor* cur = NULL;
+ if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
+ // Marked the global in-use list head so process the list.
+ while (true) {
+ const oop obj = (oop) cur->object();
+ const markWord mark = cur->header();
ResourceMark rm;
out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT
- " %s", p2i(jt), p2i(n), n->is_busy() != 0,
- mark.hash() != 0, n->owner() != NULL, p2i(obj),
+ " %s", p2i(jt), p2i(cur), cur->is_busy() != 0,
+ mark.hash() != 0, cur->owner() != NULL, p2i(obj),
obj->klass()->external_name());
- if (n->is_busy() != 0) {
- out->print(" (%s)", n->is_busy_to_string(&ss));
+ if (cur->is_busy() != 0) {
+ out->print(" (%s)", cur->is_busy_to_string(&ss));
ss.reset();
}
out->cr();
+
+ cur = lock_next_for_traversal(cur);
+ if (cur == NULL) {
+ break;
+ }
+ }
}
}
out->flush();
}
@@ -2147,22 +2546,26 @@
int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
int pop_count = 0;
out->print_cr("%18s %10s %10s %10s",
"Global Lists:", "InUse", "Free", "Total");
out->print_cr("================== ========== ========== ==========");
- out->print_cr("%18s %10d %10d %10d", "",
- g_om_in_use_count, g_om_free_count, g_om_population);
- pop_count += g_om_in_use_count + g_om_free_count;
+ int l_in_use_count = Atomic::load(&LVars.in_use_count);
+ int l_free_count = Atomic::load(&LVars.free_count);
+ out->print_cr("%18s %10d %10d %10d", "", l_in_use_count,
+ l_free_count, Atomic::load(&LVars.population));
+ pop_count += l_in_use_count + l_free_count;
out->print_cr("%18s %10s %10s %10s",
"Per-Thread Lists:", "InUse", "Free", "Provision");
out->print_cr("================== ========== ========== ==========");
for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
+ int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
+ int l_om_free_count = Atomic::load(&jt->om_free_count);
out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt),
- jt->om_in_use_count, jt->om_free_count, jt->om_free_provision);
- pop_count += jt->om_in_use_count + jt->om_free_count;
+ l_om_in_use_count, l_om_free_count, jt->om_free_provision);
+ pop_count += l_om_in_use_count + l_om_free_count;
}
return pop_count;
}
#ifndef PRODUCT
@@ -2170,21 +2573,23 @@
// Check if monitor belongs to the monitor cache
// The list is grow-only so it's *relatively* safe to traverse
// the list of extant blocks without taking a lock.
int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
- PaddedObjectMonitor* block = Atomic::load_acquire(&g_block_list);
+ PaddedObjectMonitor* block = Atomic::load(&g_block_list);
while (block != NULL) {
assert(block->object() == CHAINMARKER, "must be a block header");
if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
address mon = (address)monitor;
address blk = (address)block;
size_t diff = mon - blk;
assert((diff % sizeof(PaddedObjectMonitor)) == 0, "must be aligned");
return 1;
}
- block = (PaddedObjectMonitor*)block->_next_om;
+ // unmarked_next() is not needed with g_block_list (no locking
+ // used with block linkage _next_om fields).
+ block = (PaddedObjectMonitor*)Atomic::load(&block->_next_om);
}
return 0;
}
#endif
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