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8223312: Utilize handshakes instead of is_thread_fully_suspended

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Reviewed-by: dholmes, rrich, dcubed, eosterlund
This commit is contained in:
Robbin Ehn 2020-10-22 15:16:50 +00:00
parent cc50c8d4f1
commit 4634dbef6d
6 changed files with 235 additions and 437 deletions
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233
src/hotspot/share/runtime/thread.cpp
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@ -534,100 +534,16 @@ void Thread::send_async_exception(oop java_thread, oop java_throwable) {
// Check if an external suspend request has completed (or has been
// cancelled). Returns true if the thread is externally suspended and
// false otherwise.
//
// The bits parameter returns information about the code path through
// the routine. Useful for debugging:
//
// set in is_ext_suspend_completed():
// 0x00000001 - routine was entered
// 0x00000010 - routine return false at end
// 0x00000100 - thread exited (return false)
// 0x00000200 - suspend request cancelled (return false)
// 0x00000400 - thread suspended (return true)
// 0x00001000 - thread is in a suspend equivalent state (return true)
// 0x00002000 - thread is native and walkable (return true)
// 0x00004000 - thread is native_trans and walkable (needed retry)
//
// set in wait_for_ext_suspend_completion():
// 0x00010000 - routine was entered
// 0x00020000 - suspend request cancelled before loop (return false)
// 0x00040000 - thread suspended before loop (return true)
// 0x00080000 - suspend request cancelled in loop (return false)
// 0x00100000 - thread suspended in loop (return true)
// 0x00200000 - suspend not completed during retry loop (return false)
// Helper class for tracing suspend wait debug bits.
//
// 0x00000100 indicates that the target thread exited before it could
// self-suspend which is not a wait failure. 0x00000200, 0x00020000 and
// 0x00080000 each indicate a cancelled suspend request so they don't
// count as wait failures either.
#define DEBUG_FALSE_BITS (0x00000010 | 0x00200000)
class TraceSuspendDebugBits : public StackObj {
private:
JavaThread * jt;
bool is_wait;
bool called_by_wait; // meaningful when !is_wait
uint32_t * bits;
public:
TraceSuspendDebugBits(JavaThread *_jt, bool _is_wait, bool _called_by_wait,
uint32_t *_bits) {
jt = _jt;
is_wait = _is_wait;
called_by_wait = _called_by_wait;
bits = _bits;
}
~TraceSuspendDebugBits() {
if (!is_wait) {
#if 1
// By default, don't trace bits for is_ext_suspend_completed() calls.
// That trace is very chatty.
return;
#else
if (!called_by_wait) {
// If tracing for is_ext_suspend_completed() is enabled, then only
// trace calls to it from wait_for_ext_suspend_completion()
return;
}
#endif
}
if (AssertOnSuspendWaitFailure || TraceSuspendWaitFailures) {
if (bits != NULL && (*bits & DEBUG_FALSE_BITS) != 0) {
MutexLocker ml(Threads_lock); // needed for get_thread_name()
ResourceMark rm;
tty->print_cr(
"Failed wait_for_ext_suspend_completion(thread=%s, debug_bits=%x)",
jt->get_thread_name(), *bits);
guarantee(!AssertOnSuspendWaitFailure, "external suspend wait failed");
}
}
}
};
#undef DEBUG_FALSE_BITS
bool JavaThread::is_ext_suspend_completed(bool called_by_wait, int delay,
uint32_t *bits) {
TraceSuspendDebugBits tsdb(this, false /* !is_wait */, called_by_wait, bits);
bool JavaThread::is_ext_suspend_completed() {
bool did_trans_retry = false; // only do thread_in_native_trans retry once
bool do_trans_retry; // flag to force the retry
*bits |= 0x00000001;
do {
do_trans_retry = false;
if (is_exiting()) {
// Thread is in the process of exiting. This is always checked
// first to reduce the risk of dereferencing a freed JavaThread.
*bits |= 0x00000100;
return false;
}
@ -635,13 +551,11 @@ bool JavaThread::is_ext_suspend_completed(bool called_by_wait, int delay,
// Suspend request is cancelled. This is always checked before
// is_ext_suspended() to reduce the risk of a rogue resume
// confusing the thread that made the suspend request.
*bits |= 0x00000200;
return false;
}
if (is_ext_suspended()) {
// thread is suspended
*bits |= 0x00000400;
return true;
}
@ -669,25 +583,21 @@ bool JavaThread::is_ext_suspend_completed(bool called_by_wait, int delay,
//
// Return true since we wouldn't be here unless there was still an
// external suspend request.
*bits |= 0x00001000;
return true;
} else if (save_state == _thread_in_native && frame_anchor()->walkable()) {
// Threads running native code will self-suspend on native==>VM/Java
// transitions. If its stack is walkable (should always be the case
// unless this function is called before the actual java_suspend()
// call), then the wait is done.
*bits |= 0x00002000;
return true;
} else if (!called_by_wait && !did_trans_retry &&
} else if (!did_trans_retry &&
save_state == _thread_in_native_trans &&
frame_anchor()->walkable()) {
// The thread is transitioning from thread_in_native to another
// thread state. check_safepoint_and_suspend_for_native_trans()
// will force the thread to self-suspend. If it hasn't gotten
// there yet we may have caught the thread in-between the native
// code check above and the self-suspend. Lucky us. If we were
// called by wait_for_ext_suspend_completion(), then it
// will be doing the retries so we don't have to.
// code check above and the self-suspend.
//
// Since we use the saved thread state in the if-statement above,
// there is a chance that the thread has already transitioned to
@ -695,8 +605,6 @@ bool JavaThread::is_ext_suspend_completed(bool called_by_wait, int delay,
// make a single unnecessary pass through the logic below. This
// doesn't hurt anything since we still do the trans retry.
*bits |= 0x00004000;
// Once the thread leaves thread_in_native_trans for another
// thread state, we break out of this retry loop. We shouldn't
// need this flag to prevent us from getting back here, but
@ -716,9 +624,9 @@ bool JavaThread::is_ext_suspend_completed(bool called_by_wait, int delay,
// (if we're a JavaThread - the WatcherThread can also call this)
// and increase delay with each retry
if (Thread::current()->is_Java_thread()) {
SR_lock()->wait(i * delay);
SR_lock()->wait(i * SuspendRetryDelay);
} else {
SR_lock()->wait_without_safepoint_check(i * delay);
SR_lock()->wait_without_safepoint_check(i * SuspendRetryDelay);
}
// check the actual thread state instead of what we saved above
@ -729,134 +637,12 @@ bool JavaThread::is_ext_suspend_completed(bool called_by_wait, int delay,
break;
}
} // end retry loop
}
} while (do_trans_retry);
*bits |= 0x00000010;
return false;
}
// Wait for an external suspend request to complete (or be cancelled).
// Returns true if the thread is externally suspended and false otherwise.
//
bool JavaThread::wait_for_ext_suspend_completion(int retries, int delay,
uint32_t *bits) {
TraceSuspendDebugBits tsdb(this, true /* is_wait */,
false /* !called_by_wait */, bits);
// local flag copies to minimize SR_lock hold time
bool is_suspended;
bool pending;
uint32_t reset_bits;
// set a marker so is_ext_suspend_completed() knows we are the caller
*bits |= 0x00010000;
// We use reset_bits to reinitialize the bits value at the top of
// each retry loop. This allows the caller to make use of any
// unused bits for their own marking purposes.
reset_bits = *bits;
{
MutexLocker ml(SR_lock(), Mutex::_no_safepoint_check_flag);
is_suspended = is_ext_suspend_completed(true /* called_by_wait */,
delay, bits);
pending = is_external_suspend();
}
// must release SR_lock to allow suspension to complete
if (!pending) {
// A cancelled suspend request is the only false return from
// is_ext_suspend_completed() that keeps us from entering the
// retry loop.
*bits |= 0x00020000;
return false;
}
if (is_suspended) {
*bits |= 0x00040000;
return true;
}
for (int i = 1; i <= retries; i++) {
*bits = reset_bits; // reinit to only track last retry
// We used to do an "os::yield_all(i)" call here with the intention
// that yielding would increase on each retry. However, the parameter
// is ignored on Linux which means the yield didn't scale up. Waiting
// on the SR_lock below provides a much more predictable scale up for
// the delay. It also provides a simple/direct point to check for any
// safepoint requests from the VMThread
{
Thread* t = Thread::current();
MonitorLocker ml(SR_lock(),
t->is_Java_thread() ? Mutex::_safepoint_check_flag : Mutex::_no_safepoint_check_flag);
// wait with safepoint check (if we're a JavaThread - the WatcherThread
// can also call this) and increase delay with each retry
ml.wait(i * delay);
is_suspended = is_ext_suspend_completed(true /* called_by_wait */,
delay, bits);
// It is possible for the external suspend request to be cancelled
// (by a resume) before the actual suspend operation is completed.
// Refresh our local copy to see if we still need to wait.
pending = is_external_suspend();
}
if (!pending) {
// A cancelled suspend request is the only false return from
// is_ext_suspend_completed() that keeps us from staying in the
// retry loop.
*bits |= 0x00080000;
return false;
}
if (is_suspended) {
*bits |= 0x00100000;
return true;
}
} // end retry loop
// thread did not suspend after all our retries
*bits |= 0x00200000;
return false;
}
// Called from API entry points which perform stack walking. If the
// associated JavaThread is the current thread, then wait_for_suspend
// is not used. Otherwise, it determines if we should wait for the
// "other" thread to complete external suspension. (NOTE: in future
// releases the suspension mechanism should be reimplemented so this
// is not necessary.)
//
bool
JavaThread::is_thread_fully_suspended(bool wait_for_suspend, uint32_t *bits) {
if (this != Thread::current()) {
// "other" threads require special handling.
if (wait_for_suspend) {
// We are allowed to wait for the external suspend to complete
// so give the other thread a chance to get suspended.
if (!wait_for_ext_suspend_completion(SuspendRetryCount,
SuspendRetryDelay, bits)) {
// Didn't make it so let the caller know.
return false;
}
}
// We aren't allowed to wait for the external suspend to complete
// so if the other thread isn't externally suspended we need to
// let the caller know.
else if (!is_ext_suspend_completed_with_lock(bits)) {
return false;
}
}
return true;
}
// GC Support
bool Thread::claim_par_threads_do(uintx claim_token) {
uintx token = _threads_do_token;
@ -2489,12 +2275,11 @@ void JavaThread::java_suspend() {
}
// suspend is done
uint32_t debug_bits = 0;
// Warning: is_ext_suspend_completed() may temporarily drop the
// SR_lock to allow the thread to reach a stable thread state if
// it is currently in a transient thread state.
if (is_ext_suspend_completed(false /* !called_by_wait */,
SuspendRetryDelay, &debug_bits)) {
if (is_ext_suspend_completed()) {
return;
}
}
@ -2548,9 +2333,7 @@ int JavaThread::java_suspend_self() {
if (this->is_suspend_equivalent()) {
// If we are self-suspending as a result of the lifting of a
// suspend equivalent condition, then the suspend_equivalent
// flag is not cleared until we set the ext_suspended flag so
// that wait_for_ext_suspend_completion() returns consistent
// results.
// flag is not cleared until we set the ext_suspended flag.
this->clear_suspend_equivalent();
}