/*
* Copyright (c) 2005, Eric Crahen
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is furnished
* to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*
*/
#ifndef __ZTSEMAPHOREIMPL_H__
#define __ZTSEMAPHOREIMPL_H__
#include "zthread/Guard.h"
#include "Debug.h"
#include "FastLock.h"
#include "Scheduling.h"
#include <assert.h>
namespace ZThread {
class Monitor;
/**
* @class SemaphoreImpl
* @author Eric Crahen <http://www.code-foo.com>
* @date <2003-07-16T20:03:20-0400>
* @version 2.2.11
*
* The SemaphoreImpl template allows how waiter lists are sorted
* to be parameteized
*/
template <typename List>
class SemaphoreImpl {
//! List of waiting events
List _waiters;
//! Serialize access to this object
FastLock _lock;
//! Current count
volatile int _count;
//! Maximum count if any
volatile int _maxCount;
//! Flag for bounded or unbounded count
volatile bool _checked;
//! Entry count
volatile int _entryCount;
public:
/**
* Create a new SemaphoreImpl. Initialzes one pthreads mutex for
* internal use.
*
* @exception Initialization_Exception thrown if resources could not be
* properly allocated
*/
SemaphoreImpl(int count, unsigned int maxCount, bool checked)
: _count(count), _maxCount(maxCount), _checked(checked), _entryCount(0) { }
~SemaphoreImpl();
void acquire();
void release();
bool tryAcquire(unsigned long timeout);
int count();
};
/**
* Destroy this SemaphoreImpl and release its resources.
*/
template <typename List>
SemaphoreImpl<List>::~SemaphoreImpl() {
#ifndef NDEBUG
if(_waiters.size() > 0) {
ZTDEBUG("** You are destroying a semaphore which is blocking %d threads. **\n", _waiters.size());
assert(0); // Destroyed semaphore while in use
}
#endif
}
/**
* Get the count for the Semaphore
*
* @return int
*/
template <typename List>
int SemaphoreImpl<List>::count() {
Guard<FastLock> g(_lock);
return _count;
}
/**
* Decrement the count, blocking when that count becomes 0 or less.
*
* @exception Interrupted_Exception thrown when the caller status is interrupted
* @exception Synchronization_Exception thrown if there is some other error.
*/
template <typename List>
void SemaphoreImpl<List>::acquire() {
// Get the monitor for the current thread
ThreadImpl* self = ThreadImpl::current();
Monitor& m = self->getMonitor();
Monitor::STATE state;
Guard<FastLock> g1(_lock);
// Update the count without waiting if possible.
if(_count > 0 && _entryCount == 0)
_count--;
// Otherwise, wait() for the lock by placing the waiter in the list
else {
++_entryCount;
_waiters.insert(self);
m.acquire();
{
Guard<FastLock, UnlockedScope> g2(g1);
state = m.wait();
}
m.release();
// Remove from waiter list, regarless of weather release() is called or
// not. The monitor is sticky, so its possible a state 'stuck' from a
// previous operation and will leave the wait() w/o release() having
// been called.
typename List::iterator i = std::find(_waiters.begin(), _waiters.end(), self);
if(i != _waiters.end())
_waiters.erase(i);
--_entryCount;
switch(state) {
// If awoke due to a notify(), update the count
case Monitor::SIGNALED:
_count--;
break;
case Monitor::INTERRUPTED:
throw Interrupted_Exception();
default:
throw Synchronization_Exception();
}
}
}
/**
* Decrement the count, blocking when it that count is 0 or less. If the timeout
* expires before the count is raise above 0, the thread will stop blocking
* and return.
*
* @exception Interrupted_Exception thrown when the caller status is interrupted
* @exception Synchronization_Exception thrown if there is some other error.
*/
template <typename List>
bool SemaphoreImpl<List>::tryAcquire(unsigned long timeout) {
// Get the monitor for the current thread
ThreadImpl* self = ThreadImpl::current();
Monitor& m = self->getMonitor();
Guard<FastLock> g1(_lock);
// Update the count without waiting if possible.
if(_count > 0 && _entryCount == 0)
_count--;
// Otherwise, wait() for the lock by placing the waiter in the list
else {
++_entryCount;
_waiters.push_back(self);
Monitor::STATE state = Monitor::TIMEDOUT;
// Don't bother waiting if the timeout is 0
if(timeout) {
m.acquire();
{
Guard<FastLock, UnlockedScope> g2(g1);
state = m.wait(timeout);
}
m.release();
}
// Remove from waiter list, regarless of weather release() is called or
// not. The monitor is sticky, so its possible a state 'stuck' from a
// previous operation and will leave the wait() w/o release() having
// been called.
typename List::iterator i = std::find(_waiters.begin(), _waiters.end(), self);
if(i != _waiters.end())
_waiters.erase(i);
--_entryCount;
switch(state) {
// If awoke due to a notify(), update the count
case Monitor::SIGNALED:
_count--;
break;
case Monitor::INTERRUPTED:
throw Interrupted_Exception();
case Monitor::TIMEDOUT:
return false;
default:
throw Synchronization_Exception();
}
}
return true;
}
/**
* Increment the count and release a waiter if there are any. If the semaphore
* is checked, then an exception will be raised if the maximum count is about to
* be exceeded.
*
* @exception InvalidOp_Exception thrown if the maximum count is exceeded while
* the checked flag is set.
*/
template <typename List>
void SemaphoreImpl<List>::release() {
Guard<FastLock> g1(_lock);
// Make sure the operation is valid
if(_checked && _count == _maxCount)
throw InvalidOp_Exception();
// Increment the count
_count++;
// Try to find a waiter with a backoff & retry scheme
for(;;) {
// Go through the list, attempt to notify() a waiter.
for(typename List::iterator i = _waiters.begin(); i != _waiters.end();) {
// Try the monitor lock, if it cant be locked skip to the next waiter
ThreadImpl* impl = *i;
Monitor& m = impl->getMonitor();
if(m.tryAcquire()) {
// Notify the monitor & remove from the waiter list so time isn't
// wasted checking it again.
i = _waiters.erase(i);
// If notify() is not sucessful, it is because the wait() has already
// been ended (killed/interrupted/notify'd)
bool woke = m.notify();
m.release();
// Once notify() succeeds, return
if(woke)
return;
} else ++i;
}
if(_waiters.empty())
return;
{ // Backoff and try again
Guard<FastLock, UnlockedScope> g2(g1);
ThreadImpl::yield();
}
}
}
class FifoSemaphoreImpl : public SemaphoreImpl<fifo_list> {
public:
FifoSemaphoreImpl(int count, unsigned int maxCount, bool checked)
/* throw(Synchronization_Exception) */
: SemaphoreImpl<fifo_list>(count, maxCount, checked) { }
};
} // namespace ZThread
#endif // __ZTSEMAPHOREIMPL_H__
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