Add a sequenced worker pool

base/threading/sequenced_worker_pool_unittest.cc

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <algorithm>
+
+#include "base/bind.h"
+#include "base/memory/ref_counted.h"
+#include "base/synchronization/condition_variable.h"
+#include "base/synchronization/lock.h"
+#include "base/threading/platform_thread.h"
+#include "base/threading/sequenced_worker_pool.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace base {
+
+// IMPORTANT NOTE:
+//
+// Many of these tests have failure modes where they'll hang forever. These
+// tests should not be flaky, and hangling indicates a type of failure. Do not
+// mark as flaky if they're hanging, it's likely an actual bug.
+
+namespace {
+
+const size_t kNumWorkerThreads = 3;
+
+// Allows a number of threads to all be blocked on the same event, and
+// provides a way to unblock a certain number of them.
+class ThreadBlocker {
+ public:
+  ThreadBlocker() : lock_(), cond_var_(&lock_), unblock_counter_(0) {
+  }
+
+  void Block() {
+    {
+      base::AutoLock lock(lock_);
+      while (unblock_counter_ == 0)
+        cond_var_.Wait();
+      unblock_counter_--;
+    }
+    cond_var_.Signal();
+  }
+
+  void Unblock(size_t count) {
+    {
+      base::AutoLock lock(lock_);
+      DCHECK(unblock_counter_ == 0);
+      unblock_counter_ = count;
+    }
+    cond_var_.Signal();
+  }
+
+ private:
+  base::Lock lock_;
+  base::ConditionVariable cond_var_;
+
+  size_t unblock_counter_;
+};
+
+class TestTracker : public base::RefCountedThreadSafe<TestTracker> {
+ public:
+  TestTracker()
+      : lock_(),
+        cond_var_(&lock_),
+        started_events_(0) {
+  }
+
+  // Each of these tasks appends the argument to the complete sequence vector
+  // so calling code can see what order they finished in.
+  void FastTask(int id) {
+    SignalWorkerDone(id);
+  }
+  void SlowTask(int id) {
+    base::PlatformThread::Sleep(1000);
+    SignalWorkerDone(id);
+  }
+
+  void BlockTask(int id, ThreadBlocker* blocker) {
+    // Note that this task has started and signal anybody waiting for that
+    // to happen.
+    {
+      base::AutoLock lock(lock_);
+      started_events_++;
+    }
+    cond_var_.Signal();
+
+    blocker->Block();
+    SignalWorkerDone(id);
+  }
+
+  // Waits until the given number of tasks have started executing.
+  void WaitUntilTasksBlocked(size_t count) {
+    {
+      base::AutoLock lock(lock_);
+      while (started_events_ < count)
+        cond_var_.Wait();
+    }
+    cond_var_.Signal();
+  }
+
+  // Blocks the current thread until at least the given number of tasks are in
+  // the completed vector, and then returns a copy.
+  std::vector<int> WaitUntilTasksComplete(size_t num_tasks) {
+    std::vector<int> ret;
+    {
+      base::AutoLock lock(lock_);
+      while (complete_sequence_.size() < num_tasks)
+        cond_var_.Wait();
+      ret = complete_sequence_;
+    }
+    cond_var_.Signal();
+    return ret;
+  }
+
+  void ClearCompleteSequence() {
+    base::AutoLock lock(lock_);
+    complete_sequence_.clear();
+    started_events_ = 0;
+  }
+
+ private:
+  void SignalWorkerDone(int id) {
+    {
+      base::AutoLock lock(lock_);
+      complete_sequence_.push_back(id);
+    }
+    cond_var_.Signal();
+  }
+
+  // Protects the complete_sequence.
+  base::Lock lock_;
+
+  base::ConditionVariable cond_var_;
+
+  // Protected by lock_.
+  std::vector<int> complete_sequence_;
+
+  // Counter of the number of "block" workers that have started.
+  size_t started_events_;
+};
+
+class SequencedWorkerPoolTest : public testing::Test,
+                                public SequencedWorkerPool::TestingObserver {
+ public:
+  SequencedWorkerPoolTest()
+      : pool_(kNumWorkerThreads, "test"),
+        tracker_(new TestTracker) {
+    pool_.SetTestingObserver(this);
+  }
+  ~SequencedWorkerPoolTest() {
+  }
+
+  virtual void SetUp() {
+  }
+  virtual void TearDown() {
+    pool_.Shutdown();
+  }
+
+  SequencedWorkerPool& pool() { return pool_; }
+  TestTracker* tracker() { return tracker_.get(); }
+
+  // Ensures that the given number of worker threads is created by adding
+  // tasks and waiting until they complete. Worker thread creation is
+  // serialized, can happen on background threads asynchronously, and doesn't
+  // happen any more at shutdown. This means that if a test posts a bunch of
+  // tasks and calls shutdown, fewer workers will be created than the test may
+  // expect.
+  //
+  // This function ensures that this condition can't happen so tests can make
+  // assumptions about the number of workers active. See the comment in
+  // PrepareToStartAdditionalThreadIfNecessary in the .cc file for more
+  // details.
+  //
+  // It will post tasks to the queue with id -1. It also assumes this is the
+  // first thing called in a test since it will clear the complete_sequence_.
+  void EnsureAllWorkersCreated() {
+    // Create a bunch of threads, all waiting. This will cause that may
+    // workers to be created.
+    ThreadBlocker blocker;
+    for (size_t i = 0; i < kNumWorkerThreads; i++) {
+      pool().PostWorkerTask(FROM_HERE,
+                            base::Bind(&TestTracker::BlockTask,
+                                       tracker(), -1, &blocker));
+    }
+    tracker()->WaitUntilTasksBlocked(kNumWorkerThreads);
+
+    // Now wake them up and wait until they're done.
+    blocker.Unblock(kNumWorkerThreads);
+    tracker()->WaitUntilTasksComplete(kNumWorkerThreads);
+
+    // Clean up the task IDs we added.
+    tracker()->ClearCompleteSequence();
+  }
+
+ protected:
+  // This closure will be executed right before the pool blocks on shutdown.
+  base::Closure before_wait_for_shutdown_;
+
+ private:
+  // SequencedWorkerPool::TestingObserver implementation.
+  virtual void WillWaitForShutdown() {
+    if (!before_wait_for_shutdown_.is_null())
+      before_wait_for_shutdown_.Run();
+  }
+
+  SequencedWorkerPool pool_;
+  scoped_refptr<TestTracker> tracker_;
+};
+
+// Checks that the given number of entries are in the tasks to complete of
+// the given tracker, and then signals the given event the given number of
+// times. This is used to wakt up blocked background threads before blocking
+// on shutdown.
+void EnsureTasksToCompleteCountAndUnblock(scoped_refptr<TestTracker> tracker,
+                                          size_t expected_tasks_to_complete,
+                                          ThreadBlocker* blocker,
+                                          size_t threads_to_awake) {
+  EXPECT_EQ(
+      expected_tasks_to_complete,
+      tracker->WaitUntilTasksComplete(expected_tasks_to_complete).size());
+
+  blocker->Unblock(threads_to_awake);
+}
+
+}  // namespace
+
+// Tests that same-named tokens have the same ID.
+TEST_F(SequencedWorkerPoolTest, NamedTokens) {
+  const std::string name1("hello");
+  SequencedWorkerPool::SequenceToken token1 =
+      pool().GetNamedSequenceToken(name1);
+
+  SequencedWorkerPool::SequenceToken token2 = pool().GetSequenceToken();
+
+  const std::string name3("goodbye");
+  SequencedWorkerPool::SequenceToken token3 =
+      pool().GetNamedSequenceToken(name3);
+
+  // All 3 tokens should be different.
+  EXPECT_FALSE(token1.Equals(token2));
+  EXPECT_FALSE(token1.Equals(token3));
+  EXPECT_FALSE(token2.Equals(token3));
+
+  // Requesting the same name again should give the same value.
+  SequencedWorkerPool::SequenceToken token1again =
+      pool().GetNamedSequenceToken(name1);
+  EXPECT_TRUE(token1.Equals(token1again));
+
+  SequencedWorkerPool::SequenceToken token3again =
+      pool().GetNamedSequenceToken(name3);
+  EXPECT_TRUE(token3.Equals(token3again));
+}
+
+// Tests that posting a bunch of tasks (many more than the number of worker
+// threads) runs them all.
+TEST_F(SequencedWorkerPoolTest, LotsOfTasks) {
+  pool().PostWorkerTask(FROM_HERE,
+                        base::Bind(&TestTracker::SlowTask, tracker(), 0));
+
+  const size_t kNumTasks = 20;
+  for (size_t i = 1; i < kNumTasks; i++) {
+    pool().PostWorkerTask(FROM_HERE,
+                          base::Bind(&TestTracker::FastTask, tracker(), i));
+  }
+
+  std::vector<int> result = tracker()->WaitUntilTasksComplete(kNumTasks);
+  EXPECT_EQ(kNumTasks, result.size());
+}
+
+// Test that tasks with the same sequence token are executed in order but don't
+// affect other tasks.
+TEST_F(SequencedWorkerPoolTest, Sequence) {
+  // Fill all the worker threads except one.
+  const size_t kNumBackgroundTasks = kNumWorkerThreads - 1;
+  ThreadBlocker background_blocker;
+  for (size_t i = 0; i < kNumBackgroundTasks; i++) {
+    pool().PostWorkerTask(FROM_HERE,
+                          base::Bind(&TestTracker::BlockTask,
+                                     tracker(), i, &background_blocker));
+  }
+  tracker()->WaitUntilTasksBlocked(kNumBackgroundTasks);
+
+  // Create two tasks with the same sequence token, one that will block on the
+  // event, and one which will just complete quickly when it's run. Since there
+  // is one worker thread free, the first task will start and then block, and
+  // the second task should be waiting.
+  ThreadBlocker blocker;
+  SequencedWorkerPool::SequenceToken token1 = pool().GetSequenceToken();
+  pool().PostSequencedWorkerTask(
+      token1, FROM_HERE,
+      base::Bind(&TestTracker::BlockTask, tracker(), 100, &blocker));
+  pool().PostSequencedWorkerTask(
+      token1, FROM_HERE,
+      base::Bind(&TestTracker::FastTask, tracker(), 101));
+  EXPECT_EQ(0u, tracker()->WaitUntilTasksComplete(0).size());
+
+  // Create another two tasks as above with a different token. These will be
+  // blocked since there are no slots to run.
+  SequencedWorkerPool::SequenceToken token2 = pool().GetSequenceToken();
+  pool().PostSequencedWorkerTask(
+      token2, FROM_HERE,
+      base::Bind(&TestTracker::FastTask, tracker(), 200));
+  pool().PostSequencedWorkerTask(
+      token2, FROM_HERE,
+      base::Bind(&TestTracker::FastTask, tracker(), 201));
+  EXPECT_EQ(0u, tracker()->WaitUntilTasksComplete(0).size());
+
+  // Let one background task complete. This should then let both tasks of
+  // token2 run to completion in order. The second task of token1 should still
+  // be blocked.
+  background_blocker.Unblock(1);
+  std::vector<int> result = tracker()->WaitUntilTasksComplete(3);
+  ASSERT_EQ(3u, result.size());
+  EXPECT_EQ(200, result[1]);
+  EXPECT_EQ(201, result[2]);
+
+  // Finish the rest of the background tasks. This should leave some workers
+  // free with the second token1 task still blocked on the first.
+  background_blocker.Unblock(kNumBackgroundTasks - 1);
+  EXPECT_EQ(kNumBackgroundTasks + 2,
+            tracker()->WaitUntilTasksComplete(kNumBackgroundTasks + 2).size());
+
+  // Allow the first task of token1 to complete. This should run the second.
+  blocker.Unblock(1);
+  result = tracker()->WaitUntilTasksComplete(kNumBackgroundTasks + 4);
+  ASSERT_EQ(kNumBackgroundTasks + 4, result.size());
+  EXPECT_EQ(100, result[result.size() - 2]);
+  EXPECT_EQ(101, result[result.size() - 1]);
+}
+
+// Tests that unrun tasks are discarded properly according to their shutdown
+// mode.
+TEST_F(SequencedWorkerPoolTest, DiscardOnShutdown) {
+  // Start tasks to take all the threads and block them.
+  EnsureAllWorkersCreated();
+  ThreadBlocker blocker;
+  for (size_t i = 0; i < kNumWorkerThreads; i++) {
+    pool().PostWorkerTask(FROM_HERE,
+                          base::Bind(&TestTracker::BlockTask,
+                                     tracker(), i, &blocker));
+  }
+  tracker()->WaitUntilTasksBlocked(kNumWorkerThreads);
+
+  // Create some tasks with different shutdown modes.
+  pool().PostWorkerTaskWithShutdownBehavior(
+      FROM_HERE,
+      base::Bind(&TestTracker::FastTask, tracker(), 100),
+      SequencedWorkerPool::CONTINUE_ON_SHUTDOWN);
+  pool().PostWorkerTaskWithShutdownBehavior(
+      FROM_HERE,
+      base::Bind(&TestTracker::FastTask, tracker(), 101),
+      SequencedWorkerPool::SKIP_ON_SHUTDOWN);
+  pool().PostWorkerTaskWithShutdownBehavior(
+      FROM_HERE,
+      base::Bind(&TestTracker::FastTask, tracker(), 102),
+      SequencedWorkerPool::BLOCK_SHUTDOWN);
+
+  // Shutdown the worker pool. This should discard all non-blocking tasks.
+  before_wait_for_shutdown_ =
+      base::Bind(&EnsureTasksToCompleteCountAndUnblock,
+                 scoped_refptr<TestTracker>(tracker()), 0,
+                 &blocker, kNumWorkerThreads);
+  pool().Shutdown();
+
+  std::vector<int> result = tracker()->WaitUntilTasksComplete(4);
+
+  // The kNumWorkerThread items should have completed, plus the BLOCK_SHUTDOWN
+  // one, in no particular order.
+  ASSERT_EQ(4u, result.size());
+  for (size_t i = 0; i < kNumWorkerThreads; i++) {
+    EXPECT_TRUE(std::find(result.begin(), result.end(), static_cast<int>(i)) !=
+                result.end());
+  }
+  EXPECT_TRUE(std::find(result.begin(), result.end(), 102) != result.end());
+}
+
+// Tests that CONTINUE_ON_SHUTDOWN tasks don't block shutdown.
+TEST_F(SequencedWorkerPoolTest, ContinueOnShutdown) {
+  EnsureAllWorkersCreated();
+  ThreadBlocker blocker;
+  pool().PostWorkerTaskWithShutdownBehavior(
+      FROM_HERE,
+      base::Bind(&TestTracker::BlockTask,
+                 tracker(), 0, &blocker),
+      SequencedWorkerPool::CONTINUE_ON_SHUTDOWN);
+  tracker()->WaitUntilTasksBlocked(1);
+
+  // This should not block. If this test hangs, it means it failed.
+  pool().Shutdown();
+
+  // The task should not have completed yet.
+  EXPECT_EQ(0u, tracker()->WaitUntilTasksComplete(0).size());
+
+  // Posting more tasks should fail.
+  EXPECT_FALSE(pool().PostWorkerTaskWithShutdownBehavior(
+      FROM_HERE, base::Bind(&TestTracker::FastTask, tracker(), 0),
+      SequencedWorkerPool::CONTINUE_ON_SHUTDOWN));
+
+  // Continue the background thread and make sure the task can complete.
+  blocker.Unblock(1);
+  std::vector<int> result = tracker()->WaitUntilTasksComplete(1);
+  EXPECT_EQ(1u, result.size());
+}
+
+}  // namespace base