criticalsection.h

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/*
 * Copyright (C) 2001-2006 Jacek Sieka, arnetheduck on gmail point com
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program 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 for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

#if !defined(CRITICAL_SECTION_H)
#define CRITICAL_SECTION_H

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000

#include "Thread.h"

class CriticalSection  
{
#ifdef _WIN32
public:
	void enter() throw() {
		EnterCriticalSection(&cs);
		dcdrun(counter++);	
	}
	void leave() throw() {
		dcassert(--counter >= 0);
		LeaveCriticalSection(&cs);
	}
	CriticalSection() throw() {
		dcdrun(counter = 0;);
		InitializeCriticalSection(&cs);
	}
	~CriticalSection() throw() {
		dcassert(counter==0);
		DeleteCriticalSection(&cs);
	}
private:
	dcdrun(long counter;);
	CRITICAL_SECTION cs;
#else
public:
	CriticalSection() throw() {
#if HAVE_DECL_PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP
		static pthread_mutex_t recmtx = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
		mtx = recmtx;
#else
#error Can not find mutex type attribute.
#endif
	}
	~CriticalSection() throw() { pthread_mutex_destroy(&mtx); }
	void enter() throw() { pthread_mutex_lock(&mtx); }
	void leave() throw() { pthread_mutex_unlock(&mtx); }
	pthread_mutex_t& getMutex() { return mtx; }
private:
	pthread_mutex_t mtx;
#endif
	CriticalSection(const CriticalSection&);
	CriticalSection& operator=(const CriticalSection&);
};

/**
 * A fast, non-recursive and unfair implementation of the Critical Section.
 * It is meant to be used in situations where the risk for lock conflict is very low, 
 * i e locks that are held for a very short time. The lock is _not_ recursive, i e if 
 * the same thread will try to grab the lock it'll hang in a never-ending loop. The lock
 * is not fair, i e the first to try to enter a locked lock is not guaranteed to be the
 * first to get it when it's freed...
 */
class FastCriticalSection {
public:
#ifdef _WIN32
	FastCriticalSection() : state(0) { }

	void enter() {
		while(Thread::safeExchange(state, 1) == 1) {
			Thread::yield();
		}
	}
	void leave() {
		Thread::safeDec(state);
	}
private:
	volatile long state;

#else
	// We have to use a pthread (nonrecursive) mutex, didn't find any test_and_set on linux...
	FastCriticalSection() { 
		static pthread_mutex_t fastmtx = PTHREAD_MUTEX_INITIALIZER;
		mtx = fastmtx;
	}
	~FastCriticalSection() { pthread_mutex_destroy(&mtx); }
	void enter() { pthread_mutex_lock(&mtx); }
	void leave() { pthread_mutex_unlock(&mtx); }
private:
	pthread_mutex_t mtx;	
#endif
};

template<class T>
class LockBase {
public:
	LockBase(T& aCs) throw() : cs(aCs)  { cs.enter(); }
	~LockBase() throw() { cs.leave(); }
private:
	LockBase& operator=(const LockBase&);
	T& cs;
};
typedef LockBase<CriticalSection> Lock;
typedef LockBase<FastCriticalSection> FastLock;

template<class T = CriticalSection>
class RWLock
{
public:
	RWLock() throw() : cs(), readers(0) { }
	~RWLock() throw() { dcassert(readers==0); }

	void enterRead() throw() {
		cs.enter();
		readers++;
		dcassert(readers < 100);
		cs.leave();
	}
	void leaveRead() throw() {
		dcassert(readers > 0);
		Thread::safeDec(readers);
	}
	void enterWrite() throw() {
		cs.enter();
		while(readers > 0) {
			Thread::yield();
		}
	}
	void leaveWrite() {
		cs.leave();
	}
private:
	T cs;
	volatile long readers;
};

template<class T = CriticalSection>
class RLock {
public:
	RLock(RWLock<T>& aRwl) throw() : rwl(aRwl)  { rwl.enterRead(); }
	~RLock() throw() { rwl.leaveRead(); }
private:
	RLock& operator=(const RLock&);
	RWLock<T>& rwl;
};

template<class T = CriticalSection>
class WLock {
public:
	WLock(RWLock<T>& aRwl) throw() : rwl(aRwl)  { rwl.enterWrite(); }
	~WLock() throw() { rwl.leaveWrite(); }
private:
	WLock& operator=(const WLock&);
	RWLock<T>& rwl;
};

#endif // !defined(CRITICAL_SECTION_H)