1/*
2 * Copyright (C) 2015-2019 Apple Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
14 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
15 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
17 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
18 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
19 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
20 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
21 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
22 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
23 * THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#include "config.h"
27#include "CompareAndSwapTest.h"
28
29#include <functional>
30#include <stdio.h>
31#include <wtf/Atomics.h>
32#include <wtf/Threading.h>
33
34class Bitmap {
35public:
36 Bitmap() { clearAll(); }
37
38 inline void clearAll();
39 inline bool concurrentTestAndSet(size_t n);
40 inline size_t numBits() const { return words * wordSize; }
41
42private:
43 static constexpr size_t Size = 4096*10;
44
45 static constexpr unsigned wordSize = sizeof(uint8_t) * 8;
46 static constexpr unsigned words = (Size + wordSize - 1) / wordSize;
47 static constexpr uint8_t one = 1;
48
49 uint8_t bits[words];
50};
51
52inline void Bitmap::clearAll()
53{
54 memset(&bits, 0, sizeof(bits));
55}
56
57inline bool Bitmap::concurrentTestAndSet(size_t n)
58{
59 uint8_t mask = one << (n % wordSize);
60 size_t index = n / wordSize;
61 uint8_t* wordPtr = &bits[index];
62 uint8_t oldValue;
63 do {
64 oldValue = *wordPtr;
65 if (oldValue & mask)
66 return true;
67 } while (!WTF::atomicCompareExchangeWeakRelaxed(wordPtr, oldValue, static_cast<uint8_t>(oldValue | mask)));
68 return false;
69}
70
71struct Data {
72 Bitmap* bitmap;
73 int id;
74 int numThreads;
75};
76
77static void setBitThreadFunc(void* p)
78{
79 Data* data = reinterpret_cast<Data*>(p);
80 Bitmap* bitmap = data->bitmap;
81 size_t numBits = bitmap->numBits();
82
83 // The computed start index here is heuristic that seems to maximize (anecdotally)
84 // the chance for the CAS issue to manifest.
85 size_t start = (numBits * (data->numThreads - data->id)) / data->numThreads;
86
87 printf(" started Thread %d\n", data->id);
88 for (size_t i = start; i < numBits; i++)
89 while (!bitmap->concurrentTestAndSet(i)) { }
90 for (size_t i = 0; i < start; i++)
91 while (!bitmap->concurrentTestAndSet(i)) { }
92
93 printf(" finished Thread %d\n", data->id);
94}
95
96void testCompareAndSwap()
97{
98 Bitmap bitmap;
99 const int numThreads = 5;
100 RefPtr<Thread> threads[numThreads];
101 Data data[numThreads];
102
103 WTF::initializeThreading();
104
105 printf("Starting %d threads for CompareAndSwap test. Test should complete without hanging.\n", numThreads);
106 for (int i = 0; i < numThreads; i++) {
107 data[i].bitmap = &bitmap;
108 data[i].id = i;
109 data[i].numThreads = numThreads;
110 threads[i] = Thread::create("setBitThreadFunc", std::bind(setBitThreadFunc, &data[i]));
111 }
112
113 printf("Waiting for %d threads to join\n", numThreads);
114 for (int i = 0; i < numThreads; i++)
115 threads[i]->waitForCompletion();
116
117 printf("PASS: CompareAndSwap test completed without a hang\n");
118}
119