2 * Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
11 #include "webrtc/system_wrappers/interface/condition_variable_wrapper.h"
13 #include "testing/gtest/include/gtest/gtest.h"
14 #include "webrtc/system_wrappers/interface/critical_section_wrapper.h"
15 #include "webrtc/system_wrappers/interface/thread_wrapper.h"
16 #include "webrtc/system_wrappers/interface/trace.h"
22 const int kLongWaitMs = 100 * 1000; // A long time in testing terms
23 const int kShortWaitMs = 2 * 1000; // Long enough for process switches to happen
25 // A Baton is one possible control structure one can build using
26 // conditional variables.
27 // A Baton is always held by one and only one active thread - unlike
28 // a lock, it can never be free.
29 // One can pass it or grab it - both calls have timeouts.
30 // Note - a production tool would guard against passing it without
31 // grabbing it first. This one is for testing, so it doesn't.
35 : giver_sect_(CriticalSectionWrapper::CreateCriticalSection()),
36 crit_sect_(CriticalSectionWrapper::CreateCriticalSection()),
37 cond_var_(ConditionVariableWrapper::CreateConditionVariable()),
48 // Pass the baton. Returns false if baton is not picked up in |max_msecs|.
49 // Only one process can pass at the same time; this property is
50 // ensured by the |giver_sect_| lock.
51 bool Pass(uint32_t max_msecs) {
52 CriticalSectionScoped cs_giver(giver_sect_);
53 CriticalSectionScoped cs(crit_sect_);
54 SignalBatonAvailable();
55 const bool result = TakeBatonIfStillFree(max_msecs);
62 // Grab the baton. Returns false if baton is not passed.
63 bool Grab(uint32_t max_msecs) {
64 CriticalSectionScoped cs(crit_sect_);
65 return WaitUntilBatonOffered(max_msecs);
69 // We don't allow polling PassCount() during a Pass()-call since there is
70 // no guarantee that |pass_count_| is incremented until the Pass()-call
71 // finishes. I.e. the Grab()-call may finish before |pass_count_| has been
73 // Thus, this function waits on giver_sect_.
74 CriticalSectionScoped cs(giver_sect_);
79 // Wait/Signal forms a classical semaphore on |being_passed_|.
80 // These functions must be called with crit_sect_ held.
81 bool WaitUntilBatonOffered(int timeout_ms) {
82 while (!being_passed_) {
83 if (!cond_var_->SleepCS(*crit_sect_, timeout_ms)) {
87 being_passed_ = false;
92 void SignalBatonAvailable() {
93 assert(!being_passed_);
98 // Timeout extension: Wait for a limited time for someone else to
99 // take it, and take it if it's not taken.
100 // Returns true if resource is taken by someone else, false
101 // if it is taken back by the caller.
102 // This function must be called with both |giver_sect_| and
103 // |crit_sect_| held.
104 bool TakeBatonIfStillFree(int timeout_ms) {
105 bool not_timeout = true;
106 while (being_passed_ && not_timeout) {
107 not_timeout = cond_var_->SleepCS(*crit_sect_, timeout_ms);
108 // If we're woken up while variable is still held, we may have
109 // gotten a wakeup destined for a grabber thread.
110 // This situation is not treated specially here.
112 if (!being_passed_) {
115 assert(!not_timeout);
116 being_passed_ = false;
121 // Lock that ensures that there is only one thread in the active
122 // part of Pass() at a time.
123 // |giver_sect_| must always be acquired before |cond_var_|.
124 CriticalSectionWrapper* giver_sect_;
125 // Lock that protects |being_passed_|.
126 CriticalSectionWrapper* crit_sect_;
127 ConditionVariableWrapper* cond_var_;
129 // Statistics information: Number of successfull passes.
133 // Function that waits on a Baton, and passes it right back.
134 // We expect these calls never to time out.
135 bool WaitingRunFunction(void* obj) {
136 Baton* the_baton = static_cast<Baton*> (obj);
137 EXPECT_TRUE(the_baton->Grab(kLongWaitMs));
138 EXPECT_TRUE(the_baton->Pass(kLongWaitMs));
142 class CondVarTest : public ::testing::Test {
146 virtual void SetUp() {
147 thread_ = ThreadWrapper::CreateThread(&WaitingRunFunction,
149 unsigned int id = 42;
150 ASSERT_TRUE(thread_->Start(id));
153 virtual void TearDown() {
154 // We have to wake the thread in order to make it obey the stop order.
155 // But we don't know if the thread has completed the run function, so
156 // we don't know if it will exit before or after the Pass.
157 // Thus, we need to pin it down inside its Run function (between Grab
159 ASSERT_TRUE(baton_.Pass(kShortWaitMs));
160 thread_->SetNotAlive();
161 ASSERT_TRUE(baton_.Grab(kShortWaitMs));
162 ASSERT_TRUE(thread_->Stop());
170 ThreadWrapper* thread_;
173 // The SetUp and TearDown functions use condition variables.
174 // This test verifies those pieces in isolation.
175 TEST_F(CondVarTest, InitFunctionsWork) {
176 // All relevant asserts are in the SetUp and TearDown functions.
179 // This test verifies that one can use the baton multiple times.
180 TEST_F(CondVarTest, PassBatonMultipleTimes) {
181 const int kNumberOfRounds = 2;
182 for (int i = 0; i < kNumberOfRounds; ++i) {
183 ASSERT_TRUE(baton_.Pass(kShortWaitMs));
184 ASSERT_TRUE(baton_.Grab(kShortWaitMs));
186 EXPECT_EQ(2 * kNumberOfRounds, baton_.PassCount());
189 } // anonymous namespace
191 } // namespace webrtc