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深入理解Java中的底层阻塞原理及实现(三)
2018-10-11 16:13:02 】 浏览:534
Tags:深入 理解 Java 底层 阻塞 原理 实现

tomic::xchg(0, &_counter) > 0) return; Thread* thread = Thread::current(); assert(thread->is_Java_thread(), "Must be JavaThread"); JavaThread *jt = (JavaThread *)thread; // Optional optimization -- avoid state transitions if there's an interrupt pending. // Check interrupt before trying to wait if (Thread::is_interrupted(thread, false)) { return; } // Next, demultiplex/decode time arguments timespec absTime; if (time < 0 || (isAbsolute && time == 0) ) { // don't wait at all return; } if (time > 0) { unpackTime(&absTime, isAbsolute, time); } // Enter safepoint region // Beware of deadlocks such as 6317397. // The per-thread Parker:: mutex is a classic leaf-lock. // In particular a thread must never block on the Threads_lock while // holding the Parker:: mutex. If safepoints are pending both the // the ThreadBlockInVM() CTOR and DTOR may grab Threads_lock. ThreadBlockInVM tbivm(jt); // Don't wait if cannot get lock since interference arises from // unblocking. Also. check interrupt before trying wait if (Thread::is_interrupted(thread, false) || pthread_mutex_trylock(_mutex) != 0) { return; } int status ; if (_counter > 0) { // no wait needed _counter = 0; status = pthread_mutex_unlock(_mutex); assert (status == 0, "invariant") ; // Paranoia to ensure our locked and lock-free paths interact // correctly with each other and Java-level accesses. OrderAccess::fence(); return; } #ifdef ASSERT // Don't catch signals while blocked; let the running threads have the signals. // (This allows a debugger to break into the running thread.) sigset_t oldsigs; sigset_t* allowdebug_blocked = os::Linux::allowdebug_blocked_signals(); pthread_sigmask(SIG_BLOCK, allowdebug_blocked, &oldsigs); #endif OSThreadWaitState osts(thread->osthread(), false /* not Object.wait() */); jt->set_suspend_equivalent(); // cleared by handle_special_suspend_equivalent_condition() or java_suspend_self() assert(_cur_index == -1, "invariant"); if (time == 0) { _cur_index = REL_INDEX; // arbitrary choice when not timed status = pthread_cond_wait (&_cond[_cur_index], _mutex) ; } else { _cur_index = isAbsolute ? ABS_INDEX : REL_INDEX; status = os::Linux::safe_cond_timedwait (&_cond[_cur_index], _mutex, &absTime) ; if (status != 0 && WorkAroundNPTLTimedWaitHang) { pthread_cond_destroy (&_cond[_cur_index]) ; pthread_cond_init (&_cond[_cur_index], isAbsolute ? NULL : os::Linux::condAttr()); } } _cur_index = -1; assert_status(status == 0 || status == EINTR || status == ETIME || status == ETIMEDOUT, status, "cond_timedwait"); #ifdef ASSERT pthread_sigmask(SIG_SETMASK, &oldsigs, NULL); #endif _counter = 0 ; status = pthread_mutex_unlock(_mutex) ; assert_status(status == 0, status, "invariant") ; // Paranoia to ensure our locked and lock-free paths interact // correctly with each other and Java-level accesses. OrderAccess::fence(); // If externally suspended while waiting, re-suspend if (jt->handle_special_suspend_equivalent_condition()) { jt->java_suspend_self(); } } // unpark 实现,相对简单些 void Parker::unpark() { int s, status ; status = pthread_mutex_lock(_mutex); assert (status == 0
深入理解Java中的底层阻塞原理及实现(三) https://www.cppentry.com/bencandy.php?fid=76&id=171257

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