形形色色的锁2

public interface Lock {
    void lock();

    void lockInterruptibly() throws InterruptedException;

    boolean tryLock();

    boolean tryLock(long time, TimeUnit unit) throws InterruptedException;

    void unlock();

    Condition newCondition();
}

public interface Condition {
	void await() throws InterruptedException;
	
	void awaitUninterruptibly();
	
	long awaitNanos(long nanosTimeout) throws InterruptedException;
	
	boolean await(long time, TimeUnit unit) throws InterruptedException;
	
	boolean awaitUntil(Date deadline) throws InterruptedException;
	
	void signal();
	
	void signalAll();
}

public class LockSupport {
	...
	public static void unpark(Thread thread) {
        if (thread != null)
            unsafe.unpark(thread);
    }
    public static void park(Object blocker) {
        Thread t = Thread.currentThread();
        setBlocker(t, blocker);
        unsafe.park(false, 0L);
        setBlocker(t, null);
    }
    ...
}

...
static JNINativeMethod methods[] = {
	...
    {"suspend0", "()V", (void *)&JVM_SuspendThread},
    {"resume0", "()V", (void *)&JVM_ResumeThread},
	...
};
JNIEXPORT void JNICALL
Java_java_lang_Thread_registerNatives(JNIEnv *env, jclass cls)
{
    (*env)->RegisterNatives(env, cls, methods, ARRAY_LENGTH(methods));
}
...

...
JVM_ENTRY(void, JVM_SuspendThread(JNIEnv* env, jobject jthread))
  JVMWrapper("JVM_SuspendThread");
    oop java_thread = JNIHandles::resolve_non_null(jthread);
  JavaThread* receiver = java_lang_Thread::thread(java_thread);

  if (receiver != NULL) {
    {
      MutexLockerEx ml(receiver->SR_lock(), Mutex::_no_safepoint_check_flag);
      if (receiver->is_external_suspend()) {
        return;
      }
      if (receiver->is_exiting()) { // thread is in the process of exiting
        return;
      }
      receiver->set_external_suspend();
    }
    receiver->java_suspend();
  }
JVM_END
...

void JavaThread::java_suspend() {
  { MutexLocker mu(Threads_lock);
    if (!Threads::includes(this) || is_exiting() || this->threadObj() == NULL) {
       return;
    }
  }

  { MutexLockerEx ml(SR_lock(), Mutex::_no_safepoint_check_flag);
    if (!is_external_suspend()) {
      // a racing resume has cancelled us; bail out now
      return;
    }

    // suspend is done
    uint32_t debug_bits = 0;
    if (is_ext_suspend_completed(false /* !called_by_wait */,
                                 SuspendRetryDelay, &debug_bits) ) {
      return;
    }
  }

  VM_ForceSafepoint vm_suspend;
  VMThread::execute(&vm_suspend);
}

// Part II of external suspension.
// A JavaThread self suspends when it detects a pending external suspend
// request. This is usually on transitions. It is also done in places
// where continuing to the next transition would surprise the caller,
// e.g., monitor entry.
//
// Returns the number of times that the thread self-suspended.
//
// Note: DO NOT call java_suspend_self() when you just want to block current
//       thread. java_suspend_self() is the second stage of cooperative
//       suspension for external suspend requests and should only be used
//       to complete an external suspend request.
//
int JavaThread::java_suspend_self() {
  ...
  while (is_external_suspend()) {
    ret++;
    this->set_ext_suspended();

    // _ext_suspended flag is cleared by java_resume()
    while (is_ext_suspended()) {
      this->SR_lock()->wait(Mutex::_no_safepoint_check_flag);
    }
  }

  return ret;
}

bool Monitor::wait(bool no_safepoint_check, long timeout, bool as_suspend_equivalent) {
  Thread * const Self = Thread::current() ;
  ...

int Monitor::IWait (Thread * Self, jlong timo) {
  ...
  for (;;) {
    if (ESelf->Notified) break ;
    int err = ParkCommon (ESelf, timo) ;
    if (err == OS_TIMEOUT || (NativeMonitorFlags & 1)) break ;
  }
  ...
  return WasOnWaitSet != 0 ;        // return true IFF timeout
}

static int ParkCommon (ParkEvent * ev, jlong timo) {
  // Diagnostic support - periodically unwedge blocked threads
  intx nmt = NativeMonitorTimeout ;
  if (nmt > 0 && (nmt < timo || timo <= 0)) {
     timo = nmt ;
  }
  int err = OS_OK ;
  if (0 == timo) {
    ev->park() ;
  } else {
    err = ev->park(timo) ;
  }
  return err ;
}

void os::PlatformEvent::park() {       // AKA "down()"
  ...
  if (v == 0) {
     ...
     while (_Event < 0) {
        status = pthread_cond_wait(_cond, _mutex);
        // for some reason, under 2.7 lwp_cond_wait() may return ETIME ...
        // Treat this the same as if the wait was interrupted
        if (status == ETIME) { status = EINTR; }
        assert_status(status == 0 || status == EINTR, status, "cond_wait");
     }
     ...
  }
}

  // The external_suspend
  // flag is checked by has_special_runtime_exit_condition() and java thread
  // will self-suspend when handle_special_runtime_exit_condition() is
  // called. Most uses of the _thread_blocked state in JavaThreads are
  // considered the same as being externally suspended; if the blocking
  // condition lifts, the JavaThread will self-suspend. Other places
  // where VM checks for external_suspend include:
  //   + mutex granting (do not enter monitors when thread is suspended)
  //   + state transitions from _thread_in_native
  //
  // In general, java_suspend() does not wait for an external suspend
  // request to complete. When it returns, the only guarantee is that
  // the _external_suspend field is true.

  bool has_special_runtime_exit_condition() {
    return (_special_runtime_exit_condition != _no_async_condition) ||
            is_external_suspend() || is_deopt_suspend();
  }

void JavaThread::handle_special_runtime_exit_condition(bool check_asyncs) {
  bool do_self_suspend = is_external_suspend_with_lock();
  if (do_self_suspend && (!AllowJNIEnvProxy || this == JavaThread::current())) {
    frame_anchor()->make_walkable(this);
    java_suspend_self();
  }

  if (check_asyncs) {
    check_and_handle_async_exceptions();
  }
}

void JavaThread::check_safepoint_and_suspend_for_native_trans(JavaThread *thread) {
  JavaThread *curJT = JavaThread::current();
  bool do_self_suspend = thread->is_external_suspend();
  ...
  if (do_self_suspend && (!AllowJNIEnvProxy || curJT == thread)) {
    JavaThreadState state = thread->thread_state();
    thread->set_thread_state(_thread_blocked);
    thread->java_suspend_self();
    thread->set_thread_state(state);
    ...
    }
  }

  if (SafepointSynchronize::do_call_back()) {
    // If we are safepointing, then block the caller which may not be
    // the same as the target thread (see above).
    SafepointSynchronize::block(curJT);
  }
  ...
}

void JavaThread::java_suspend() {
  ...
  VM_ForceSafepoint vm_suspend;
  VMThread::execute(&vm_suspend);
  ...
}

// dummy vm op, evaluated just to force a safepoint
class VM_ForceSafepoint: public VM_Operation {
 public:
  VM_ForceSafepoint() {}
  void doit()         {}
  VMOp_Type type() const { return VMOp_ForceSafepoint; }
};

static JNINativeMethod methods[] = {
    {"hashCode",    "()I",                    (void *)&JVM_IHashCode},
    {"wait",        "(J)V",                   (void *)&JVM_MonitorWait},
    {"notify",      "()V",                    (void *)&JVM_MonitorNotify},
    {"notifyAll",   "()V",                    (void *)&JVM_MonitorNotifyAll},
    {"clone",       "()Ljava/lang/Object;",   (void *)&JVM_Clone},
};

JNIEXPORT void JNICALL
Java_java_lang_Object_registerNatives(JNIEnv *env, jclass cls)
{
    (*env)->RegisterNatives(env, cls,
                            methods, sizeof(methods)/sizeof(methods[0]));
}

JVM_ENTRY(void, JVM_MonitorWait(JNIEnv* env, jobject handle, jlong ms))
  JVMWrapper("JVM_MonitorWait");
  Handle obj(THREAD, JNIHandles::resolve_non_null(handle));
  JavaThreadInObjectWaitState jtiows(thread, ms != 0);
  if (JvmtiExport::should_post_monitor_wait()) {
    JvmtiExport::post_monitor_wait((JavaThread *)THREAD, (oop)obj(), ms);
  }
  ObjectSynchronizer::wait(obj, ms, CHECK);
JVM_END

void ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
  ...
  ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
  DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
  monitor->wait(millis, true, THREAD);
  ...
}

void ObjectMonitor::wait(jlong millis, bool interruptible, TRAPS) {
   ...
   int ret = OS_OK ;
   int WasNotified = 0 ;
   { // State transition wrappers
     OSThread* osthread = Self->osthread();
     OSThreadWaitState osts(osthread, true);
     {
       ThreadBlockInVM tbivm(jt);
       // Thread is in thread_blocked state and oop access is unsafe.
       jt->set_suspend_equivalent();

       if (interruptible && (Thread::is_interrupted(THREAD, false) || HAS_PENDING_EXCEPTION)) {
           // Intentionally empty
       } else
       if (node._notified == 0) {
         if (millis <= 0) {
            Self->_ParkEvent->park () ;
         } else {
            ret = Self->_ParkEvent->park (millis) ;
         }
       }

       // were we externally suspended while we were waiting?
       if (ExitSuspendEquivalent (jt)) {
          // TODO-FIXME: add -- if succ == Self then succ = null.
          jt->java_suspend_self();
       }

     } 
    ...
}

public final class Unsafe {
    ...
    public native void unpark(Object thread);
    public native void park(boolean isAbsolute, long time);
    ...
}

static JNINativeMethod methods_18[] = {
    ...
    {CC"park",               CC"(ZJ)V",                  FN_PTR(Unsafe_Park)},
    {CC"unpark",             CC"("OBJ")V",               FN_PTR(Unsafe_Unpark)}
    ...
}

UNSAFE_ENTRY(void, Unsafe_Park(JNIEnv *env, jobject unsafe, jboolean isAbsolute, jlong time))
  UnsafeWrapper("Unsafe_Park");
  EventThreadPark event;
#ifndef USDT2
  HS_DTRACE_PROBE3(hotspot, thread__park__begin, thread->parker(), (int) isAbsolute, time);
#else /* USDT2 */
   HOTSPOT_THREAD_PARK_BEGIN(
                             (uintptr_t) thread->parker(), (int) isAbsolute, time);
#endif /* USDT2 */
  JavaThreadParkedState jtps(thread, time != 0);
  thread->parker()->park(isAbsolute != 0, time);
#ifndef USDT2
  HS_DTRACE_PROBE1(hotspot, thread__park__end, thread->parker());
#else /* USDT2 */
  HOTSPOT_THREAD_PARK_END(
                          (uintptr_t) thread->parker());
#endif /* USDT2 */
  if (event.should_commit()) {
    oop obj = thread->current_park_blocker();
    event.set_klass((obj != NULL) ? obj->klass() : NULL);
    event.set_timeout(time);
    event.set_address((obj != NULL) ? (TYPE_ADDRESS) cast_from_oop<uintptr_t>(obj) : 0);
    event.commit();
  }
UNSAFE_END

class Parker : public os::PlatformParker {
  ...
public:
  void park(bool isAbsolute, jlong time);
  void unpark();
  ...
}

void Parker::park(bool isAbsolute, jlong time) {
  if (Atomic::xchg(0, &_counter) > 0) return;

  Thread* thread = Thread::current();
  JavaThread *jt = (JavaThread *)thread;

  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);
  }

  ThreadBlockInVM tbivm(jt);

  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);
    OrderAccess::fence();
    return;
  }
  ...
  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());
    }
  }
  ...
  // If externally suspended while waiting, re-suspend
  if (jt->handle_special_suspend_equivalent_condition()) {
    jt->java_suspend_self();
  }
}

void Parker::unpark() {
  int s, status ;
  status = pthread_mutex_lock(_mutex);
  assert (status == 0, "invariant") ;
  s = _counter;
  _counter = 1;
  if (s < 1) {
    // thread might be parked
    if (_cur_index != -1) {
      // thread is definitely parked
      if (WorkAroundNPTLTimedWaitHang) {
        status = pthread_cond_signal (&_cond[_cur_index]);
        status = pthread_mutex_unlock(_mutex);
      } else {
        status = pthread_mutex_unlock(_mutex);
        status = pthread_cond_signal (&_cond[_cur_index]);
      }
    } else {
      pthread_mutex_unlock(_mutex);
    }
  } else {
    pthread_mutex_unlock(_mutex);
  }
}

    public final void acquire(int arg) {
        if (!tryAcquire(arg) &&
            acquireQueued(addWaiter(Node.EXCLUSIVE), arg))
            selfInterrupt();
    }

    private Node addWaiter(Node mode) {
        Node node = new Node(Thread.currentThread(), mode);
        // Try the fast path of enq; backup to full enq on failure
        Node pred = tail;
        if (pred != null) {
            node.prev = pred;
            if (compareAndSetTail(pred, node)) {
                pred.next = node;
                return node;
            }
        }
        enq(node);
        return node;
    }

    private Node enq(final Node node) {
        for (;;) {
            Node t = tail;
            if (t == null) { // Must initialize
                if (compareAndSetHead(new Node()))
                    tail = head;
            } else {
                node.prev = t;
                if (compareAndSetTail(t, node)) {
                    t.next = node;
                    return t;
                }
            }
        }
    }

    final boolean acquireQueued(final Node node, int arg) {
        boolean failed = true;
        try {
            boolean interrupted = false;
            for (;;) {
                final Node p = node.predecessor();
                if (p == head && tryAcquire(arg)) {
                    setHead(node);
                    p.next = null; // help GC
                    failed = false;
                    return interrupted;
                }
                if (shouldParkAfterFailedAcquire(p, node) &&
                    parkAndCheckInterrupt())
                    interrupted = true;
            }
        } finally {
            if (failed)
                cancelAcquire(node);
        }
    }

    public final boolean release(int arg) {
        if (tryRelease(arg)) {
            Node h = head;
            if (h != null && h.waitStatus != 0)
                unparkSuccessor(h);
            return true;
        }
        return false;
    }

    private void unparkSuccessor(Node node) {
        /*
         * If status is negative (i.e., possibly needing signal) try
         * to clear in anticipation of signalling.  It is OK if this
         * fails or if status is changed by waiting thread.
         */
        int ws = node.waitStatus;
        if (ws < 0)
            compareAndSetWaitStatus(node, ws, 0);

        /*
         * Thread to unpark is held in successor, which is normally
         * just the next node.  But if cancelled or apparently null,
         * traverse backwards from tail to find the actual
         * non-cancelled successor.
         */
        Node s = node.next;
        if (s == null || s.waitStatus > 0) {
            s = null;
            for (Node t = tail; t != null && t != node; t = t.prev)
                if (t.waitStatus <= 0)
                    s = t;
        }
        if (s != null)
            LockSupport.unpark(s.thread);
    }

final boolean acquireQueued(final Node node, int arg) {
       ...
            for (;;) {
                final Node p = node.predecessor();
                if (p == head && tryAcquire(arg)) {
                    setHead(node);
                    p.next = null; // help GC
                    failed = false;
                    return interrupted;
                }
                if (shouldParkAfterFailedAcquire(p, node) &&
                    parkAndCheckInterrupt())
                    interrupted = true;
            }
      ...
    }

    public final void acquireShared(int arg) {
        if (tryAcquireShared(arg) < 0)
            doAcquireShared(arg);
    }

   private void doAcquireShared(int arg) {
        final Node node = addWaiter(Node.SHARED);
        boolean failed = true;
        try {
            boolean interrupted = false;
            for (;;) {
                final Node p = node.predecessor();
                if (p == head) {
                    int r = tryAcquireShared(arg);
                    if (r >= 0) {
                        setHeadAndPropagate(node, r);
                        p.next = null; // help GC
                        if (interrupted)
                            selfInterrupt();
                        failed = false;
                        return;
                    }
                }
                if (shouldParkAfterFailedAcquire(p, node) &&
                    parkAndCheckInterrupt())
                    interrupted = true;
            }
        } finally {
            if (failed)
                cancelAcquire(node);
        }
    }

static final int SHARED_SHIFT   = 16;
static final int SHARED_UNIT    = (1 << SHARED_SHIFT);
static final int MAX_COUNT      = (1 << SHARED_SHIFT) - 1;
static final int EXCLUSIVE_MASK = (1 << SHARED_SHIFT) - 1;

/** Returns the number of shared holds represented in count  */
static int sharedCount(int c)    { return c >>> SHARED_SHIFT; }
/** Returns the number of exclusive holds represented in count  */
static int exclusiveCount(int c) { return c & EXCLUSIVE_MASK; }

protected final int tryAcquireShared(int unused) {
            /*
             * Walkthrough:
             * 1. If write lock held by another thread, fail.
             * 2. Otherwise, this thread is eligible for
             *    lock wrt state, so ask if it should block
             *    because of queue policy. If not, try
             *    to grant by CASing state and updating count.
             *    Note that step does not check for reentrant
             *    acquires, which is postponed to full version
             *    to avoid having to check hold count in
             *    the more typical non-reentrant case.
             * 3. If step 2 fails either because thread
             *    apparently not eligible or CAS fails or count
             *    saturated, chain to version with full retry loop.
             */
            Thread current = Thread.currentThread();
            int c = getState();
            if (exclusiveCount(c) != 0 &&
                getExclusiveOwnerThread() != current)
                return -1;
            int r = sharedCount(c);
            if (!readerShouldBlock() &&
                r < MAX_COUNT &&
                compareAndSetState(c, c + SHARED_UNIT)) {
                if (r == 0) {
                    firstReader = current;
                    firstReaderHoldCount = 1;
                } else if (firstReader == current) {
                    firstReaderHoldCount++;
                } else {
                    HoldCounter rh = cachedHoldCounter;
                    if (rh == null || rh.tid != getThreadId(current))
                        cachedHoldCounter = rh = readHolds.get();
                    else if (rh.count == 0)
                        readHolds.set(rh);
                    rh.count++;
                }
                return 1;
            }
            return fullTryAcquireShared(current);
        }

protected final boolean tryAcquire(int acquires) {
            /*
             * Walkthrough:
             * 1. If read count nonzero or write count nonzero
             *    and owner is a different thread, fail.
             * 2. If count would saturate, fail. (This can only
             *    happen if count is already nonzero.)
             * 3. Otherwise, this thread is eligible for lock if
             *    it is either a reentrant acquire or
             *    queue policy allows it. If so, update state
             *    and set owner.
             */
            Thread current = Thread.currentThread();
            int c = getState();
            int w = exclusiveCount(c);
            if (c != 0) {
                // (Note: if c != 0 and w == 0 then shared count != 0)
                if (w == 0 || current != getExclusiveOwnerThread())
                    return false;
                if (w + exclusiveCount(acquires) > MAX_COUNT)
                    throw new Error("Maximum lock count exceeded");
                // Reentrant acquire
                setState(c + acquires);
                return true;
            }
            if (writerShouldBlock() ||
                !compareAndSetState(c, c + acquires))
                return false;
            setExclusiveOwnerThread(current);
            return true;
        }

abstract static class Sync extends AbstractQueuedSynchronizer {
  ...
  final boolean nonfairTryAcquire(int acquires) {
            final Thread current = Thread.currentThread();
            int c = getState();
            if (c == 0) {
                if (compareAndSetState(0, acquires)) {
                    setExclusiveOwnerThread(current);
                    return true;
                }
            }
            else if (current == getExclusiveOwnerThread()) {
                int nextc = c + acquires;
                if (nextc < 0) // overflow
                    throw new Error("Maximum lock count exceeded");
                setState(nextc);
                return true;
            }
            return false;
  }
  ...
}

static final class NonfairSync extends Sync {
        ...
        protected final boolean tryAcquire(int acquires) {
            return nonfairTryAcquire(acquires);
        }
}

 static final class FairSync extends Sync {
        ...
        protected final boolean tryAcquire(int acquires) {
            final Thread current = Thread.currentThread();
            int c = getState();
            if (c == 0) {
                if (!hasQueuedPredecessors() &&
                    compareAndSetState(0, acquires)) {
                    setExclusiveOwnerThread(current);
                    return true;
                }
            }
            else if (current == getExclusiveOwnerThread()) {
                int nextc = c + acquires;
                if (nextc < 0)
                    throw new Error("Maximum lock count exceeded");
                setState(nextc);
                return true;
            }
            return false;
        }
}

    public final void acquireInterruptibly(int arg)
            throws InterruptedException {
        if (Thread.interrupted())
            throw new InterruptedException();
        if (!tryAcquire(arg))
            doAcquireInterruptibly(arg);
    }

 private void doAcquireInterruptibly(int arg)
        throws InterruptedException {
        final Node node = addWaiter(Node.EXCLUSIVE);
        boolean failed = true;
        try {
            for (;;) {
                final Node p = node.predecessor();
                if (p == head && tryAcquire(arg)) {
                    setHead(node);
                    p.next = null; // help GC
                    failed = false;
                    return;
                }
                if (shouldParkAfterFailedAcquire(p, node) &&
                    parkAndCheckInterrupt())
                    // 注意：这里不再是记录标记为而是直接抛
                    // 中断异常来跳出循环
                    throw new InterruptedException();
            }
        } finally {
            if (failed)
                cancelAcquire(node);
        }
    }