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CompareAndSwapTest.cpp
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122 lines (101 loc) · 3.92 KB
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/*
* Copyright (C) 2015-2019 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "CompareAndSwapTest.h"
#include <functional>
#include <stdio.h>
#include <wtf/Atomics.h>
#include <wtf/Threading.h>
WTF_ALLOW_UNSAFE_BUFFER_USAGE_BEGIN
class Bitmap {
public:
Bitmap() { clearAll(); }
inline void clearAll();
inline bool concurrentTestAndSet(size_t n);
inline size_t NODELETE numBits() const { return words * wordSize; }
private:
static constexpr size_t Size = 4096*10;
static constexpr unsigned wordSize = sizeof(uint8_t) * 8;
static constexpr unsigned words = (Size + wordSize - 1) / wordSize;
static constexpr uint8_t one = 1;
uint8_t bits[words];
};
inline void Bitmap::clearAll()
{
memset(&bits, 0, sizeof(bits));
}
inline bool NODELETE Bitmap::concurrentTestAndSet(size_t n)
{
uint8_t mask = one << (n % wordSize);
size_t index = n / wordSize;
uint8_t* wordPtr = &bits[index];
uint8_t oldValue;
do {
oldValue = *wordPtr;
if (oldValue & mask)
return true;
} while (!WTF::atomicCompareExchangeWeakRelaxed(wordPtr, oldValue, static_cast<uint8_t>(oldValue | mask)));
return false;
}
struct Data {
Bitmap* bitmap;
int id;
int numThreads;
};
static void setBitThreadFunc(void* p)
{
Data* data = reinterpret_cast<Data*>(p);
Bitmap* bitmap = data->bitmap;
size_t numBits = bitmap->numBits();
// The computed start index here is heuristic that seems to maximize (anecdotally)
// the chance for the CAS issue to manifest.
size_t start = (numBits * (data->numThreads - data->id)) / data->numThreads;
printf(" started Thread %d\n", data->id);
for (size_t i = start; i < numBits; i++)
while (!bitmap->concurrentTestAndSet(i)) { }
for (size_t i = 0; i < start; i++)
while (!bitmap->concurrentTestAndSet(i)) { }
printf(" finished Thread %d\n", data->id);
}
void testCompareAndSwap()
{
Bitmap bitmap;
const int numThreads = 5;
RefPtr<Thread> threads[numThreads];
Data data[numThreads];
WTF::initialize();
printf("Starting %d threads for CompareAndSwap test. Test should complete without hanging.\n", numThreads);
for (int i = 0; i < numThreads; i++) {
data[i].bitmap = &bitmap;
data[i].id = i;
data[i].numThreads = numThreads;
threads[i] = Thread::create("setBitThreadFunc"_s, std::bind(setBitThreadFunc, &data[i]));
}
printf("Waiting for %d threads to join\n", numThreads);
for (int i = 0; i < numThreads; i++)
threads[i]->waitForCompletion();
printf("PASS: CompareAndSwap test completed without a hang\n");
}
WTF_ALLOW_UNSAFE_BUFFER_USAGE_END