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src/hotspot/share/runtime/handshake.cpp
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@@ -35,55 +35,53 @@
#include "runtime/thread.hpp"
#include "runtime/vmThread.hpp"
#include "utilities/formatBuffer.hpp"
#include "utilities/preserveException.hpp"
-class HandshakeOperation: public StackObj {
-public:
- virtual void do_handshake(JavaThread* thread) = 0;
-};
-class HandshakeThreadsOperation: public HandshakeOperation {
- static Semaphore _done;
+class HandshakeOperation: public StackObj {
HandshakeClosure* _handshake_cl;
+ int32_t _pending_threads;
bool _executed;
+ bool _is_direct;
public:
- HandshakeThreadsOperation(HandshakeClosure* cl) : _handshake_cl(cl), _executed(false) {}
+ HandshakeOperation(HandshakeClosure* cl, bool is_direct = false) :
+ _handshake_cl(cl),
+ _pending_threads(1),
+ _executed(false),
+ _is_direct(is_direct) {}
+
void do_handshake(JavaThread* thread);
- bool thread_has_completed() { return _done.trywait(); }
+ bool is_completed() {
+ int32_t val = Atomic::load(&_pending_threads);
+ assert(val >= 0, "_pending_threads cannot be negative");
+ return val == 0;
+ }
+ void add_target_count(int count) { Atomic::add(&_pending_threads, count); }
bool executed() const { return _executed; }
const char* name() { return _handshake_cl->name(); }
+ bool is_direct() { return _is_direct; }
+
#ifdef ASSERT
void check_state() {
- assert(!_done.trywait(), "Must be zero");
+ assert(_pending_threads == 0, "Must be zero");
}
#endif
};
-Semaphore HandshakeThreadsOperation::_done(0);
-
class VM_Handshake: public VM_Operation {
const jlong _handshake_timeout;
public:
bool evaluate_at_safepoint() const { return false; }
protected:
- HandshakeThreadsOperation* const _op;
+ HandshakeOperation* const _op;
- VM_Handshake(HandshakeThreadsOperation* op) :
+ VM_Handshake(HandshakeOperation* op) :
_handshake_timeout(TimeHelper::millis_to_counter(HandshakeTimeout)), _op(op) {}
- void set_handshake(JavaThread* target) {
- target->set_handshake_operation(_op);
- }
-
- // This method returns true for threads completed their operation
- // and true for threads canceled their operation.
- // A cancellation can happen if the thread is exiting.
- bool poll_for_completed_thread() { return _op->thread_has_completed(); }
-
bool handshake_has_timed_out(jlong start_time);
static void handle_timeout();
};
bool VM_Handshake::handshake_has_timed_out(jlong start_time) {
@@ -119,24 +117,22 @@
}
class VM_HandshakeOneThread: public VM_Handshake {
JavaThread* _target;
public:
- VM_HandshakeOneThread(HandshakeThreadsOperation* op, JavaThread* target) :
+ VM_HandshakeOneThread(HandshakeOperation* op, JavaThread* target) :
VM_Handshake(op), _target(target) {}
void doit() {
- DEBUG_ONLY(_op->check_state();)
-
jlong start_time_ns = 0;
if (log_is_enabled(Info, handshake)) {
start_time_ns = os::javaTimeNanos();
}
ThreadsListHandle tlh;
if (tlh.includes(_target)) {
- set_handshake(_target);
+ _target->set_handshake_operation(_op);
} else {
log_handshake_info(start_time_ns, _op->name(), 0, 0, "(thread dead)");
return;
}
@@ -145,12 +141,12 @@
bool by_vm_thread = false;
do {
if (handshake_has_timed_out(timeout_start_time)) {
handle_timeout();
}
- by_vm_thread = _target->handshake_try_process_by_vmThread();
- } while (!poll_for_completed_thread());
+ by_vm_thread = _target->handshake_try_process(_op);
+ } while (!_op->is_completed());
DEBUG_ONLY(_op->check_state();)
log_handshake_info(start_time_ns, _op->name(), 1, by_vm_thread ? 1 : 0);
}
VMOp_Type type() const { return VMOp_HandshakeOneThread; }
@@ -158,36 +154,35 @@
bool executed() const { return _op->executed(); }
};
class VM_HandshakeAllThreads: public VM_Handshake {
public:
- VM_HandshakeAllThreads(HandshakeThreadsOperation* op) : VM_Handshake(op) {}
+ VM_HandshakeAllThreads(HandshakeOperation* op) : VM_Handshake(op) {}
void doit() {
- DEBUG_ONLY(_op->check_state();)
-
jlong start_time_ns = 0;
if (log_is_enabled(Info, handshake)) {
start_time_ns = os::javaTimeNanos();
}
int handshake_executed_by_vm_thread = 0;
JavaThreadIteratorWithHandle jtiwh;
int number_of_threads_issued = 0;
for (JavaThread *thr = jtiwh.next(); thr != NULL; thr = jtiwh.next()) {
- set_handshake(thr);
+ thr->set_handshake_operation(_op);
number_of_threads_issued++;
}
if (number_of_threads_issued < 1) {
log_handshake_info(start_time_ns, _op->name(), 0, 0);
return;
}
+ // _op was created with a count == 1 so don't double count.
+ _op->add_target_count(number_of_threads_issued - 1);
log_trace(handshake)("Threads signaled, begin processing blocked threads by VMThread");
const jlong start_time = os::elapsed_counter();
- int number_of_threads_completed = 0;
do {
// Check if handshake operation has timed out
if (handshake_has_timed_out(start_time)) {
handle_timeout();
}
@@ -196,31 +191,25 @@
// Observing a blocked state may of course be transient but the processing is guarded
// by semaphores and we optimistically begin by working on the blocked threads
jtiwh.rewind();
for (JavaThread *thr = jtiwh.next(); thr != NULL; thr = jtiwh.next()) {
// A new thread on the ThreadsList will not have an operation,
- // hence it is skipped in handshake_process_by_vmthread.
- if (thr->handshake_try_process_by_vmThread()) {
+ // hence it is skipped in handshake_try_process.
+ if (thr->handshake_try_process(_op)) {
handshake_executed_by_vm_thread++;
}
}
- while (poll_for_completed_thread()) {
- // Includes canceled operations by exiting threads.
- number_of_threads_completed++;
- }
-
- } while (number_of_threads_issued > number_of_threads_completed);
- assert(number_of_threads_issued == number_of_threads_completed, "Must be the same");
+ } while (!_op->is_completed());
DEBUG_ONLY(_op->check_state();)
log_handshake_info(start_time_ns, _op->name(), number_of_threads_issued, handshake_executed_by_vm_thread);
}
VMOp_Type type() const { return VMOp_HandshakeAllThreads; }
};
-void HandshakeThreadsOperation::do_handshake(JavaThread* thread) {
+void HandshakeOperation::do_handshake(JavaThread* thread) {
jlong start_time_ns = 0;
if (log_is_enabled(Debug, handshake, task)) {
start_time_ns = os::javaTimeNanos();
}
@@ -234,137 +223,204 @@
jlong completion_time = os::javaTimeNanos() - start_time_ns;
log_debug(handshake, task)("Operation: %s for thread " PTR_FORMAT ", is_vm_thread: %s, completed in " JLONG_FORMAT " ns",
name(), p2i(thread), BOOL_TO_STR(Thread::current()->is_VM_thread()), completion_time);
}
- // Use the semaphore to inform the VM thread that we have completed the operation
- _done.signal();
+ // Inform VMThread/Handshaker that we have completed the operation
+ Atomic::dec(&_pending_threads);
- // It is no longer safe to refer to 'this' as the VMThread may have destroyed this operation
+ // It is no longer safe to refer to 'this' as the VMThread/Handshaker may have destroyed this operation
}
void Handshake::execute(HandshakeClosure* thread_cl) {
- HandshakeThreadsOperation cto(thread_cl);
+ HandshakeOperation cto(thread_cl);
VM_HandshakeAllThreads handshake(&cto);
VMThread::execute(&handshake);
}
bool Handshake::execute(HandshakeClosure* thread_cl, JavaThread* target) {
- HandshakeThreadsOperation cto(thread_cl);
+ HandshakeOperation cto(thread_cl);
VM_HandshakeOneThread handshake(&cto, target);
VMThread::execute(&handshake);
return handshake.executed();
}
-HandshakeState::HandshakeState() : _operation(NULL), _semaphore(1), _thread_in_process_handshake(false) {
- DEBUG_ONLY(_vmthread_processing_handshake = false;)
-}
+bool Handshake::execute_direct(HandshakeClosure* thread_cl, JavaThread* target) {
+ JavaThread* self = JavaThread::current();
+ HandshakeOperation op(thread_cl, /*is_direct*/ true);
+
+ jlong start_time_ns = 0;
+ if (log_is_enabled(Info, handshake)) {
+ start_time_ns = os::javaTimeNanos();
+ }
+
+ ThreadsListHandle tlh;
+ if (tlh.includes(target)) {
+ target->set_handshake_operation(&op);
+ } else {
+ log_handshake_info(start_time_ns, op.name(), 0, 0, "(thread dead)");
+ return false;
+ }
-void HandshakeState::set_operation(JavaThread* target, HandshakeOperation* op) {
+ bool by_handshaker = false;
+ while (!op.is_completed()) {
+ by_handshaker = target->handshake_try_process(&op);
+ // Check for pending handshakes to avoid possible deadlocks where our
+ // target is trying to handshake us.
+ if (SafepointMechanism::should_block(self)) {
+ ThreadBlockInVM tbivm(self);
+ }
+ }
+ DEBUG_ONLY(op.check_state();)
+ log_handshake_info(start_time_ns, op.name(), 1, by_handshaker ? 1 : 0);
+
+ return op.executed();
+}
+
+HandshakeState::HandshakeState() :
+ _operation(NULL),
+ _operation_direct(NULL),
+ _handshake_turn_sem(1),
+ _processing_sem(1),
+ _thread_in_process_handshake(false)
+{
+ DEBUG_ONLY(_active_handshaker = NULL;)
+}
+
+void HandshakeState::set_operation(HandshakeOperation* op) {
+ if (!op->is_direct()) {
+ assert(Thread::current()->is_VM_thread(), "should be the VMThread");
_operation = op;
- SafepointMechanism::arm_local_poll_release(target);
+ } else {
+ assert(Thread::current()->is_Java_thread(), "should be a JavaThread");
+ // Serialize direct handshakes so that only one proceeds at a time for a given target
+ _handshake_turn_sem.wait_with_safepoint_check(JavaThread::current());
+ _operation_direct = op;
+ }
+ SafepointMechanism::arm_local_poll_release(_handshakee);
}
-void HandshakeState::clear_handshake(JavaThread* target) {
+void HandshakeState::clear_handshake(bool is_direct) {
+ if (!is_direct) {
_operation = NULL;
- SafepointMechanism::disarm_if_needed(target, true /* release */);
+ } else {
+ _operation_direct = NULL;
+ _handshake_turn_sem.signal();
+ }
}
-void HandshakeState::process_self_inner(JavaThread* thread) {
- assert(Thread::current() == thread, "should call from thread");
- assert(!thread->is_terminated(), "should not be a terminated thread");
- assert(thread->thread_state() != _thread_blocked, "should not be in a blocked state");
- assert(thread->thread_state() != _thread_in_native, "should not be in native");
+void HandshakeState::process_self_inner() {
+ assert(Thread::current() == _handshakee, "should call from _handshakee");
+ assert(!_handshakee->is_terminated(), "should not be a terminated thread");
+ assert(_handshakee->thread_state() != _thread_blocked, "should not be in a blocked state");
+ assert(_handshakee->thread_state() != _thread_in_native, "should not be in native");
+ JavaThread* self = _handshakee;
do {
- ThreadInVMForHandshake tivm(thread);
- if (!_semaphore.trywait()) {
- _semaphore.wait_with_safepoint_check(thread);
+ ThreadInVMForHandshake tivm(self);
+ if (!_processing_sem.trywait()) {
+ _processing_sem.wait_with_safepoint_check(self);
+ }
+ if (has_operation()) {
+ HandleMark hm(self);
+ CautiouslyPreserveExceptionMark pem(self);
+ HandshakeOperation * op = _operation;
+ if (op != NULL) {
+ // Disarm before executing the operation
+ clear_handshake(/*is_direct*/ false);
+ op->do_handshake(self);
}
- HandshakeOperation* op = Atomic::load_acquire(&_operation);
+ op = _operation_direct;
if (op != NULL) {
- HandleMark hm(thread);
- CautiouslyPreserveExceptionMark pem(thread);
- // Disarm before execute the operation
- clear_handshake(thread);
- op->do_handshake(thread);
+ // Disarm before executing the operation
+ clear_handshake(/*is_direct*/ true);
+ op->do_handshake(self);
}
- _semaphore.signal();
+ }
+ _processing_sem.signal();
} while (has_operation());
}
-bool HandshakeState::vmthread_can_process_handshake(JavaThread* target) {
+bool HandshakeState::can_process_handshake() {
// handshake_safe may only be called with polls armed.
- // VM thread controls this by first claiming the handshake via claim_handshake_for_vmthread.
- return SafepointSynchronize::handshake_safe(target);
+ // Handshaker controls this by first claiming the handshake via claim_handshake().
+ return SafepointSynchronize::handshake_safe(_handshakee);
}
-static bool possibly_vmthread_can_process_handshake(JavaThread* target) {
+bool HandshakeState::possibly_can_process_handshake() {
// Note that this method is allowed to produce false positives.
- if (target->is_ext_suspended()) {
+ if (_handshakee->is_ext_suspended()) {
return true;
}
- if (target->is_terminated()) {
+ if (_handshakee->is_terminated()) {
return true;
}
- switch (target->thread_state()) {
+ switch (_handshakee->thread_state()) {
case _thread_in_native:
// native threads are safe if they have no java stack or have walkable stack
- return !target->has_last_Java_frame() || target->frame_anchor()->walkable();
+ return !_handshakee->has_last_Java_frame() || _handshakee->frame_anchor()->walkable();
case _thread_blocked:
return true;
default:
return false;
}
}
-bool HandshakeState::claim_handshake_for_vmthread() {
- if (!_semaphore.trywait()) {
+bool HandshakeState::claim_handshake(bool is_direct) {
+ if (!_processing_sem.trywait()) {
return false;
}
- if (has_operation()) {
+ if (has_specific_operation(is_direct)){
return true;
}
- _semaphore.signal();
+ _processing_sem.signal();
return false;
}
-bool HandshakeState::try_process_by_vmThread(JavaThread* target) {
- assert(Thread::current()->is_VM_thread(), "should call from vm thread");
+bool HandshakeState::try_process(HandshakeOperation* op) {
+ bool is_direct = op->is_direct();
- if (!has_operation()) {
+ if (!has_specific_operation(is_direct)){
// JT has already cleared its handshake
return false;
}
- if (!possibly_vmthread_can_process_handshake(target)) {
+ if (!possibly_can_process_handshake()) {
// JT is observed in an unsafe state, it must notice the handshake itself
return false;
}
// Claim the semaphore if there still an operation to be executed.
- if (!claim_handshake_for_vmthread()) {
+ if (!claim_handshake(is_direct)) {
+ return false;
+ }
+
+ // Check if the handshake operation is the same as the one we meant to execute. The
+ // handshake could have been already processed by the handshakee and a new handshake
+ // by another JavaThread might be in progress.
+ if ( (is_direct && op != _operation_direct)) {
+ _processing_sem.signal();
return false;
}
// If we own the semaphore at this point and while owning the semaphore
// can observe a safe state the thread cannot possibly continue without
// getting caught by the semaphore.
bool executed = false;
- if (vmthread_can_process_handshake(target)) {
- guarantee(!_semaphore.trywait(), "we should already own the semaphore");
- log_trace(handshake)("Processing handshake by VMThtread");
- DEBUG_ONLY(_vmthread_processing_handshake = true;)
- _operation->do_handshake(target);
- DEBUG_ONLY(_vmthread_processing_handshake = false;)
- // Disarm after VM thread have executed the operation.
- clear_handshake(target);
+ if (can_process_handshake()) {
+ guarantee(!_processing_sem.trywait(), "we should already own the semaphore");
+ log_trace(handshake)("Processing handshake by %s", Thread::current()->is_VM_thread() ? "VMThread" : "Handshaker");
+ DEBUG_ONLY(_active_handshaker = Thread::current();)
+ op->do_handshake(_handshakee);
+ DEBUG_ONLY(_active_handshaker = NULL;)
+ // Disarm after we have executed the operation.
+ clear_handshake(is_direct);
executed = true;
}
// Release the thread
- _semaphore.signal();
+ _processing_sem.signal();
return executed;
}
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