about summary refs log tree commit diff
path: root/absl/base/spinlock_test_common.cc
blob: b68c51a1dcde2296aadcd6a1f95236b38bfe3a55 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
// Copyright 2017 The Abseil Authors.
//
// Licensed 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
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// A bunch of threads repeatedly hash an array of ints protected by a
// spinlock.  If the spinlock is working properly, all elements of the
// array should be equal at the end of the test.

#include <cstdint>
#include <limits>
#include <random>
#include <thread>  // NOLINT(build/c++11)
#include <vector>

#include "gtest/gtest.h"
#include "absl/base/attributes.h"
#include "absl/base/internal/low_level_scheduling.h"
#include "absl/base/internal/scheduling_mode.h"
#include "absl/base/internal/spinlock.h"
#include "absl/base/internal/sysinfo.h"
#include "absl/base/macros.h"
#include "absl/synchronization/blocking_counter.h"
#include "absl/synchronization/notification.h"

constexpr int32_t kNumThreads = 10;
constexpr int32_t kIters = 1000;

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace base_internal {

// This is defined outside of anonymous namespace so that it can be
// a friend of SpinLock to access protected methods for testing.
struct SpinLockTest {
  static uint32_t EncodeWaitCycles(int64_t wait_start_time,
                                   int64_t wait_end_time) {
    return SpinLock::EncodeWaitCycles(wait_start_time, wait_end_time);
  }
  static uint64_t DecodeWaitCycles(uint32_t lock_value) {
    return SpinLock::DecodeWaitCycles(lock_value);
  }
};

namespace {

static constexpr int kArrayLength = 10;
static uint32_t values[kArrayLength];

ABSL_CONST_INIT static SpinLock static_cooperative_spinlock(
    absl::kConstInit, base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL);
ABSL_CONST_INIT static SpinLock static_noncooperative_spinlock(
    absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY);

// Simple integer hash function based on the public domain lookup2 hash.
// http://burtleburtle.net/bob/c/lookup2.c
static uint32_t Hash32(uint32_t a, uint32_t c) {
  uint32_t b = 0x9e3779b9UL;  // The golden ratio; an arbitrary value.
  a -= b; a -= c; a ^= (c >> 13);
  b -= c; b -= a; b ^= (a << 8);
  c -= a; c -= b; c ^= (b >> 13);
  a -= b; a -= c; a ^= (c >> 12);
  b -= c; b -= a; b ^= (a << 16);
  c -= a; c -= b; c ^= (b >> 5);
  a -= b; a -= c; a ^= (c >> 3);
  b -= c; b -= a; b ^= (a << 10);
  c -= a; c -= b; c ^= (b >> 15);
  return c;
}

static void TestFunction(int thread_salt, SpinLock* spinlock) {
  for (int i = 0; i < kIters; i++) {
    SpinLockHolder h(spinlock);
    for (int j = 0; j < kArrayLength; j++) {
      const int index = (j + thread_salt) % kArrayLength;
      values[index] = Hash32(values[index], thread_salt);
      std::this_thread::yield();
    }
  }
}

static void ThreadedTest(SpinLock* spinlock) {
  std::vector<std::thread> threads;
  for (int i = 0; i < kNumThreads; ++i) {
    threads.push_back(std::thread(TestFunction, i, spinlock));
  }
  for (auto& thread : threads) {
    thread.join();
  }

  SpinLockHolder h(spinlock);
  for (int i = 1; i < kArrayLength; i++) {
    EXPECT_EQ(values[0], values[i]);
  }
}

TEST(SpinLock, StackNonCooperativeDisablesScheduling) {
  SpinLock spinlock(base_internal::SCHEDULE_KERNEL_ONLY);
  spinlock.Lock();
  EXPECT_FALSE(base_internal::SchedulingGuard::ReschedulingIsAllowed());
  spinlock.Unlock();
}

TEST(SpinLock, StaticNonCooperativeDisablesScheduling) {
  static_noncooperative_spinlock.Lock();
  EXPECT_FALSE(base_internal::SchedulingGuard::ReschedulingIsAllowed());
  static_noncooperative_spinlock.Unlock();
}

TEST(SpinLock, WaitCyclesEncoding) {
  // These are implementation details not exported by SpinLock.
  const int kProfileTimestampShift = 7;
  const int kLockwordReservedShift = 3;
  const uint32_t kSpinLockSleeper = 8;

  // We should be able to encode up to (1^kMaxCycleBits - 1) without clamping
  // but the lower kProfileTimestampShift will be dropped.
  const int kMaxCyclesShift =
    32 - kLockwordReservedShift + kProfileTimestampShift;
  const uint64_t kMaxCycles = (int64_t{1} << kMaxCyclesShift) - 1;

  // These bits should be zero after encoding.
  const uint32_t kLockwordReservedMask = (1 << kLockwordReservedShift) - 1;

  // These bits are dropped when wait cycles are encoded.
  const uint64_t kProfileTimestampMask = (1 << kProfileTimestampShift) - 1;

  // Test a bunch of random values
  std::default_random_engine generator;
  // Shift to avoid overflow below.
  std::uniform_int_distribution<uint64_t> time_distribution(
      0, std::numeric_limits<uint64_t>::max() >> 4);
  std::uniform_int_distribution<uint64_t> cycle_distribution(0, kMaxCycles);

  for (int i = 0; i < 100; i++) {
    int64_t start_time = time_distribution(generator);
    int64_t cycles = cycle_distribution(generator);
    int64_t end_time = start_time + cycles;
    uint32_t lock_value = SpinLockTest::EncodeWaitCycles(start_time, end_time);
    EXPECT_EQ(0, lock_value & kLockwordReservedMask);
    uint64_t decoded = SpinLockTest::DecodeWaitCycles(lock_value);
    EXPECT_EQ(0, decoded & kProfileTimestampMask);
    EXPECT_EQ(cycles & ~kProfileTimestampMask, decoded);
  }

  // Test corner cases
  int64_t start_time = time_distribution(generator);
  EXPECT_EQ(kSpinLockSleeper,
            SpinLockTest::EncodeWaitCycles(start_time, start_time));
  EXPECT_EQ(0, SpinLockTest::DecodeWaitCycles(0));
  EXPECT_EQ(0, SpinLockTest::DecodeWaitCycles(kLockwordReservedMask));
  EXPECT_EQ(kMaxCycles & ~kProfileTimestampMask,
            SpinLockTest::DecodeWaitCycles(~kLockwordReservedMask));

  // Check that we cannot produce kSpinLockSleeper during encoding.
  int64_t sleeper_cycles =
      kSpinLockSleeper << (kProfileTimestampShift - kLockwordReservedShift);
  uint32_t sleeper_value =
      SpinLockTest::EncodeWaitCycles(start_time, start_time + sleeper_cycles);
  EXPECT_NE(sleeper_value, kSpinLockSleeper);

  // Test clamping
  uint32_t max_value =
    SpinLockTest::EncodeWaitCycles(start_time, start_time + kMaxCycles);
  uint64_t max_value_decoded = SpinLockTest::DecodeWaitCycles(max_value);
  uint64_t expected_max_value_decoded = kMaxCycles & ~kProfileTimestampMask;
  EXPECT_EQ(expected_max_value_decoded, max_value_decoded);

  const int64_t step = (1 << kProfileTimestampShift);
  uint32_t after_max_value =
    SpinLockTest::EncodeWaitCycles(start_time, start_time + kMaxCycles + step);
  uint64_t after_max_value_decoded =
      SpinLockTest::DecodeWaitCycles(after_max_value);
  EXPECT_EQ(expected_max_value_decoded, after_max_value_decoded);

  uint32_t before_max_value = SpinLockTest::EncodeWaitCycles(
      start_time, start_time + kMaxCycles - step);
  uint64_t before_max_value_decoded =
    SpinLockTest::DecodeWaitCycles(before_max_value);
  EXPECT_GT(expected_max_value_decoded, before_max_value_decoded);
}

TEST(SpinLockWithThreads, StackSpinLock) {
  SpinLock spinlock;
  ThreadedTest(&spinlock);
}

TEST(SpinLockWithThreads, StackCooperativeSpinLock) {
  SpinLock spinlock(base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL);
  ThreadedTest(&spinlock);
}

TEST(SpinLockWithThreads, StackNonCooperativeSpinLock) {
  SpinLock spinlock(base_internal::SCHEDULE_KERNEL_ONLY);
  ThreadedTest(&spinlock);
}

TEST(SpinLockWithThreads, StaticCooperativeSpinLock) {
  ThreadedTest(&static_cooperative_spinlock);
}

TEST(SpinLockWithThreads, StaticNonCooperativeSpinLock) {
  ThreadedTest(&static_noncooperative_spinlock);
}

TEST(SpinLockWithThreads, DoesNotDeadlock) {
  struct Helper {
    static void NotifyThenLock(Notification* locked, SpinLock* spinlock,
                               BlockingCounter* b) {
      locked->WaitForNotification();  // Wait for LockThenWait() to hold "s".
      b->DecrementCount();
      SpinLockHolder l(spinlock);
    }

    static void LockThenWait(Notification* locked, SpinLock* spinlock,
                             BlockingCounter* b) {
      SpinLockHolder l(spinlock);
      locked->Notify();
      b->Wait();
    }

    static void DeadlockTest(SpinLock* spinlock, int num_spinners) {
      Notification locked;
      BlockingCounter counter(num_spinners);
      std::vector<std::thread> threads;

      threads.push_back(
          std::thread(Helper::LockThenWait, &locked, spinlock, &counter));
      for (int i = 0; i < num_spinners; ++i) {
        threads.push_back(
            std::thread(Helper::NotifyThenLock, &locked, spinlock, &counter));
      }

      for (auto& thread : threads) {
        thread.join();
      }
    }
  };

  SpinLock stack_cooperative_spinlock(
      base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL);
  SpinLock stack_noncooperative_spinlock(base_internal::SCHEDULE_KERNEL_ONLY);
  Helper::DeadlockTest(&stack_cooperative_spinlock,
                       base_internal::NumCPUs() * 2);
  Helper::DeadlockTest(&stack_noncooperative_spinlock,
                       base_internal::NumCPUs() * 2);
  Helper::DeadlockTest(&static_cooperative_spinlock,
                       base_internal::NumCPUs() * 2);
  Helper::DeadlockTest(&static_noncooperative_spinlock,
                       base_internal::NumCPUs() * 2);
}

}  // namespace
}  // namespace base_internal
ABSL_NAMESPACE_END
}  // namespace absl