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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*
* This file is part of the LibreOffice project.
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* This file incorporates work covered by the following license notice:
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed
* with this work for additional information regarding copyright
* ownership. The ASF licenses this file to you under the Apache
* License, Version 2.0 (the "License"); you may not use this file
* except in compliance with the License. You may obtain a copy of
* the License at http://www.apache.org/licenses/LICENSE-2.0 .
*/
#include <sal/main.h>
#include <osl/mutex.h>
#include <osl/conditn.h>
#include <osl/thread.h>
#include <cstdio>
#include <cassert>
#define BUFFER_SIZE 10
bool queue[9];
sal_uInt32 nItemCount = 0;
oslCondition fullOrEmpty;
oslMutex queueMutex;
oslThread producer, consumer;
void add();
void remove();
void produce(void*);
void consume(void*);
SAL_IMPLEMENT_MAIN()
{
fprintf(stdout, "Producer/consumer problem - demonstrates mutex, condition variables and threads.\n");
queueMutex = osl_createMutex();
fullOrEmpty = osl_createCondition();
producer = osl_createThread(produce, nullptr);
consumer = osl_createThread(consume, nullptr);
osl_joinWithThread(consumer);
return 0;
}
void produce(void* /* pData */)
{
osl_setThreadName("producer");
while(true)
{
/* producer monitor - first acquire exclusive access to
the queue, if the queue is full then wait till there
is space made available. Once the queue is no longer
full, then notify that this is the case.
*/
osl_acquireMutex(queueMutex);
while (nItemCount == BUFFER_SIZE-1)
{
/* we aren't doing anything to the queue, so release
the mutex and then reacquire it after waiting.
Without this, we eventually hit a "missed wakeup"
condition, whereby the thread is sleeping due to
waiting on the condition variable, but another
thread preemptively switched right before the
thread went to sleep and another thread sets the
condition variable... but of course then it switches
back to this thread which then waits forever as it
has missed its wakeup event...
*/
osl_releaseMutex(queueMutex);
osl_waitCondition(fullOrEmpty, nullptr);
osl_acquireMutex(queueMutex);
}
fprintf(stdout, "produce()\n");
add();
osl_setCondition(fullOrEmpty);
osl_releaseMutex(queueMutex);
osl_yieldThread();
}
fprintf(stderr, "exit produce()!\n");
}
void consume(void* /* pData */)
{
osl_setThreadName("consumer");
while(true)
{
/* consumer monitor - first acquire exclusive access to the
queue, if the queue is empty then wait till something is
produced. Once the queue is no longer empty, then notify
that this is the case.
*/
osl_acquireMutex(queueMutex);
while (nItemCount == 0)
{
/* We aren't doing anything to the queue, so release
the mutex and then reacquire it after waiting. See
comments in produce() for the reasoning.
*/
osl_releaseMutex(queueMutex);
osl_waitCondition(fullOrEmpty, nullptr);
osl_acquireMutex(queueMutex);
}
fprintf(stdout, "consume()\n");
remove();
osl_setCondition(fullOrEmpty);
osl_releaseMutex(queueMutex);
osl_yieldThread();
}
fprintf(stderr, "exit consume()!\n");
}
void add()
{
queue[nItemCount] = true;
fprintf(stdout, "Adding to queue - item %d added.\n", nItemCount);
nItemCount++;
assert(nItemCount <= BUFFER_SIZE-1);
}
void remove()
{
queue[nItemCount] = false;
fprintf(stdout, "Removing from queue - item %d removed.\n", nItemCount);
nItemCount--;
assert(nItemCount >= 0);
}
/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
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