< prev index next >
src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp
Print this page
rev 7209 : [mq]: inccms
*** 62,85 ****
static bool CMS_flag_is_set(int b) { return (_CMS_flag & b) != 0; }
static bool set_CMS_flag(int b) { return (_CMS_flag |= b) != 0; }
static bool clear_CMS_flag(int b) { return (_CMS_flag &= ~b) != 0; }
void sleepBeforeNextCycle();
! // CMS thread should yield for a young gen collection, direct allocation,
! // and iCMS activity.
static char _pad_1[64 - sizeof(jint)]; // prevent cache-line sharing
static volatile jint _pending_yields;
- static volatile jint _pending_decrements; // decrements to _pending_yields
static char _pad_2[64 - sizeof(jint)]; // prevent cache-line sharing
// Tracing messages, enabled by CMSTraceThreadState.
static inline void trace_state(const char* desc);
- static volatile int _icms_disabled; // a counter to track #iCMS disable & enable
- static volatile bool _should_run; // iCMS may run
- static volatile bool _should_stop; // iCMS should stop
-
// debugging
void verify_ok_to_terminate() const PRODUCT_RETURN;
public:
// Constructor
--- 62,79 ----
static bool CMS_flag_is_set(int b) { return (_CMS_flag & b) != 0; }
static bool set_CMS_flag(int b) { return (_CMS_flag |= b) != 0; }
static bool clear_CMS_flag(int b) { return (_CMS_flag &= ~b) != 0; }
void sleepBeforeNextCycle();
! // CMS thread should yield for a young gen collection and direct allocations
static char _pad_1[64 - sizeof(jint)]; // prevent cache-line sharing
static volatile jint _pending_yields;
static char _pad_2[64 - sizeof(jint)]; // prevent cache-line sharing
// Tracing messages, enabled by CMSTraceThreadState.
static inline void trace_state(const char* desc);
// debugging
void verify_ok_to_terminate() const PRODUCT_RETURN;
public:
// Constructor
*** 133,234 ****
// of 0 indicates that there is no upper bound on the wait time.
// A concurrent full gc request terminates the wait.
void wait_on_cms_lock_for_scavenge(long t_millis);
// The CMS thread will yield during the work portion of its cycle
! // only when requested to. Both synchronous and asychronous requests
! // are provided:
! // (1) A synchronous request is used for young gen collections and
// for direct allocations. The requesting thread increments
// _pending_yields at the beginning of an operation, and decrements
// _pending_yields when that operation is completed.
// In turn, the CMS thread yields when _pending_yields is positive,
// and continues to yield until the value reverts to 0.
- // (2) An asynchronous request, on the other hand, is used by iCMS
- // for the stop_icms() operation. A single yield satisfies all of
- // the outstanding asynch yield requests, of which there may
- // occasionally be several in close succession. To accomplish
- // this, an asynch-requesting thread atomically increments both
- // _pending_yields and _pending_decrements. An asynchr requesting
- // thread does not wait and "acknowledge" completion of an operation
- // and deregister the request, like the synchronous version described
- // above does. In turn, after yielding, the CMS thread decrements both
- // _pending_yields and _pending_decrements by the value seen in
- // _pending_decrements before the decrement.
- // NOTE: The above scheme is isomorphic to having two request counters,
- // one for async requests and one for sync requests, and for the CMS thread
- // to check the sum of the two counters to decide whether it should yield
- // and to clear only the async counter when it yields. However, it turns out
- // to be more efficient for CMS code to just check a single counter
- // _pending_yields that holds the sum (of both sync and async requests), and
- // a second counter _pending_decrements that only holds the async requests,
- // for greater efficiency, since in a typical CMS run, there are many more
- // potential (i.e. static) yield points than there are actual
- // (i.e. dynamic) yields because of requests, which are few and far between.
- //
- // Note that, while "_pending_yields >= _pending_decrements" is an invariant,
- // we cannot easily test that invariant, since the counters are manipulated via
- // atomic instructions without explicit locking and we cannot read
- // the two counters atomically together: one suggestion is to
- // use (for example) 16-bit counters so as to be able to read the
- // two counters atomically even on 32-bit platforms. Notice that
- // the second assert in acknowledge_yield_request() below does indeed
- // check a form of the above invariant, albeit indirectly.
static void increment_pending_yields() {
Atomic::inc(&_pending_yields);
assert(_pending_yields >= 0, "can't be negative");
}
static void decrement_pending_yields() {
Atomic::dec(&_pending_yields);
assert(_pending_yields >= 0, "can't be negative");
}
- static void asynchronous_yield_request() {
- assert(CMSIncrementalMode, "Currently only used w/iCMS");
- increment_pending_yields();
- Atomic::inc(&_pending_decrements);
- assert(_pending_decrements >= 0, "can't be negative");
- }
- static void acknowledge_yield_request() {
- jint decrement = _pending_decrements;
- if (decrement > 0) {
- assert(CMSIncrementalMode, "Currently only used w/iCMS");
- // Order important to preserve: _pending_yields >= _pending_decrements
- Atomic::add(-decrement, &_pending_decrements);
- Atomic::add(-decrement, &_pending_yields);
- assert(_pending_decrements >= 0, "can't be negative");
- assert(_pending_yields >= 0, "can't be negative");
- }
- }
static bool should_yield() { return _pending_yields > 0; }
-
- // CMS incremental mode.
- static void start_icms(); // notify thread to start a quantum of work
- static void stop_icms(); // request thread to stop working
- void icms_wait(); // if asked to stop, wait until notified to start
-
- // Incremental mode is enabled globally by the flag CMSIncrementalMode. It
- // must also be enabled/disabled dynamically to allow foreground collections.
- #define ICMS_ENABLING_ASSERT \
- assert((CMSIncrementalMode && _icms_disabled >= 0) || \
- (!CMSIncrementalMode && _icms_disabled <= 0), "Error")
-
- static inline void enable_icms() {
- ICMS_ENABLING_ASSERT;
- Atomic::dec(&_icms_disabled);
- }
- static inline void disable_icms() {
- ICMS_ENABLING_ASSERT;
- Atomic::inc(&_icms_disabled);
- }
- static inline bool icms_is_disabled() {
- ICMS_ENABLING_ASSERT;
- return _icms_disabled > 0;
- }
- static inline bool icms_is_enabled() {
- return !icms_is_disabled();
- }
};
inline void ConcurrentMarkSweepThread::trace_state(const char* desc) {
if (CMSTraceThreadState) {
char buf[128];
--- 127,153 ----
// of 0 indicates that there is no upper bound on the wait time.
// A concurrent full gc request terminates the wait.
void wait_on_cms_lock_for_scavenge(long t_millis);
// The CMS thread will yield during the work portion of its cycle
! // only when requested to.
! // A synchronous request is used for young gen collections and
// for direct allocations. The requesting thread increments
// _pending_yields at the beginning of an operation, and decrements
// _pending_yields when that operation is completed.
// In turn, the CMS thread yields when _pending_yields is positive,
// and continues to yield until the value reverts to 0.
static void increment_pending_yields() {
Atomic::inc(&_pending_yields);
assert(_pending_yields >= 0, "can't be negative");
}
static void decrement_pending_yields() {
Atomic::dec(&_pending_yields);
assert(_pending_yields >= 0, "can't be negative");
}
static bool should_yield() { return _pending_yields > 0; }
};
inline void ConcurrentMarkSweepThread::trace_state(const char* desc) {
if (CMSTraceThreadState) {
char buf[128];
< prev index next >