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/*
* Copyright 2001 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
* CA 95054 USA or visit www.sun.com if you need additional information or
* have any questions.
*
*/
#include <stdio.h>
#include <assert.h>
#include "Monitor.hpp"
Monitor::Monitor() {
_lock_count = -1; // No threads have entered the critical section
_owner = NULL;
_lock_event = CreateEvent(NULL, false, false, NULL);
_wait_event = CreateEvent(NULL, true, false, NULL);
_counter = 0;
_tickets = 0;
_waiters = 0;
}
Monitor::~Monitor() {
assert(_owner == NULL); // Otherwise, owned monitor being deleted
assert(_lock_count == -1); // Otherwise, monitor being deleted with non -1 lock count
CloseHandle(_lock_event);
CloseHandle(_wait_event);
}
void
Monitor::lock() {
if (InterlockedIncrement(&_lock_count) == 0) {
// Success, we now own the lock
} else {
DWORD dwRet = WaitForSingleObject((HANDLE)_lock_event, INFINITE);
assert(dwRet == WAIT_OBJECT_0); // Unexpected return value from WaitForSingleObject
}
assert(owner() == NULL); // Otherwise, lock count and owner are inconsistent
setOwner(GetCurrentThread());
}
void
Monitor::unlock() {
setOwner(NULL);
if (InterlockedDecrement(&_lock_count) >= 0) {
// Wake a waiting thread up
DWORD dwRet = SetEvent(_lock_event);
assert(dwRet != 0); // Unexpected return value from SetEvent
}
}
bool
Monitor::wait(long timeout) {
assert(owner() != NULL);
assert(owner() == GetCurrentThread());
// 0 means forever. Convert to Windows specific code.
DWORD timeout_value = (timeout == 0) ? INFINITE : timeout;
DWORD which;
long c = _counter;
bool retry = false;
_waiters++;
// Loop until condition variable is signaled. The event object is
// set whenever the condition variable is signaled, and tickets will
// reflect the number of threads which have been notified. The counter
// field is used to make sure we don't respond to notifications that
// have occurred *before* we started waiting, and is incremented each
// time the condition variable is signaled.
while (true) {
// Leave critical region
unlock();
// If this is a retry, let other low-priority threads have a chance
// to run. Make sure that we sleep outside of the critical section.
if (retry) {
Sleep(1);
} else {
retry = true;
}
which = WaitForSingleObject(_wait_event, timeout_value);
// Enter critical section
lock();
if (_tickets != 0 && _counter != c) break;
if (which == WAIT_TIMEOUT) {
--_waiters;
return true;
}
}
_waiters--;
// If this was the last thread to be notified, then we need to reset
// the event object.
if (--_tickets == 0) {
ResetEvent(_wait_event);
}
return false;
}
// Notify a single thread waiting on this monitor
bool
Monitor::notify() {
assert(ownedBySelf()); // Otherwise, notify on unknown thread
if (_waiters > _tickets) {
if (!SetEvent(_wait_event)) {
return false;
}
_tickets++;
_counter++;
}
return true;
}
// Notify all threads waiting on this monitor
bool
Monitor::notifyAll() {
assert(ownedBySelf()); // Otherwise, notifyAll on unknown thread
if (_waiters > 0) {
if (!SetEvent(_wait_event)) {
return false;
}
_tickets = _waiters;
_counter++;
}
return true;
}
HANDLE
Monitor::owner() {
return _owner;
}
void
Monitor::setOwner(HANDLE owner) {
if (owner != NULL) {
assert(_owner == NULL); // Setting owner thread of already owned monitor
assert(owner == GetCurrentThread()); // Else should not be doing this
} else {
HANDLE oldOwner = _owner;
assert(oldOwner != NULL); // Removing the owner thread of an unowned mutex
assert(oldOwner == GetCurrentThread());
}
_owner = owner;
}
bool
Monitor::ownedBySelf() {
return (_owner == GetCurrentThread());
}
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