Add a SharedMemSynchronizer class.

media/audio/shared_mem_synchronizer_unittest.cc

Index: media/audio/shared_mem_synchronizer_unittest.cc
diff --git a/media/audio/shared_mem_synchronizer_unittest.cc b/media/audio/shared_mem_synchronizer_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..f58c6e2aaa3a879c1a071ce0b530f7357bbb1f54
--- /dev/null
+++ b/media/audio/shared_mem_synchronizer_unittest.cc
@@ -0,0 +1,450 @@
+// Copyright (c) 2012 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 "base/compiler_specific.h"
+#include "base/logging.h"
+#include "base/shared_memory.h"
+#include "base/test/multiprocess_test.h"
+#include "base/threading/platform_thread.h"
+#include "media/audio/shared_mem_synchronizer.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "testing/multiprocess_func_list.h"
+
+namespace {
+

[Ami GONE FROM CHROMIUM, 2012/03/13 20:08:02]

Any reason to use a stack array instead of just using a vector to start with?

[tommi (sloooow) - chröme, 2012/03/14 13:32:43]

Done.

The alternative is to have two loops, one for construction and another for
deletion for both arrays.  The stack array did the latter for me.  I don't feel
strongly about this so I removed the stack arrays and wrote a little class that
does this for me using STLDeleteElements.  Stack arrays are gone.

+// A convenience method to populate a vector of SharedMemSynchronizer pointers
+// from an on-stack array.
+void PopulateVectorFromStackArray(
+    SharedMemSynchronizer::SynchronizerVector* synchronizers,
+    SharedMemSynchronizer* array,
+    size_t count) {
+  synchronizers->resize(count);
+  for (size_t i = 0; i < count; ++i)
+    (*synchronizers)[i] = &array[i];
+}
+
+// A simple thread that we'll run two instances of.  Both threads get
+// a pointer to the same |shared_data| and use a SharedMemSynchronizer to
+// control when each thread can read/write.
+class SingleSynchronizerWorker : public base::PlatformThread::Delegate {
+ public:
+  SingleSynchronizerWorker(size_t* shared_data, size_t repeats,
+                           SharedMemSynchronizer* synchronizer)
+      : shared_data_(shared_data), repeats_(repeats),
+        synchronizer_(synchronizer) {
+  }
+  virtual ~SingleSynchronizerWorker() {}
+
+  virtual void ThreadMain() OVERRIDE {
+    for (size_t i = 0; i < repeats_; ++i) {
+      synchronizer_->Wait();
+      ++(*shared_data_);
+      synchronizer_->Signal();
+    }
+  }
+
+ private:
+  size_t* shared_data_;
+  size_t repeats_;
+  SharedMemSynchronizer* synchronizer_;
+  DISALLOW_COPY_AND_ASSIGN(SingleSynchronizerWorker);
+};
+
+// Similar to SingleSynchronizerWorker, except each instance of this class will
+// have >1 instances of SharedMemSynchronizer to Wait/Signal and an equal amount
+// of |shared_data| that the synchronizers control access to.
+class MultiSynchronizerWorker : public base::PlatformThread::Delegate {
+ public:
+  MultiSynchronizerWorker(size_t* shared_data, size_t repeats,
+      const SharedMemSynchronizer::SynchronizerVector* synchronizers)
+      : shared_data_(shared_data), repeats_(repeats),
+        synchronizers_(synchronizers) {
+  }
+  virtual ~MultiSynchronizerWorker() {}
+
+  virtual void ThreadMain() OVERRIDE {
+    SharedMemSynchronizer::WaitForMultiple waiter(synchronizers_);
+    for (size_t i = 0; i < repeats_; ++i) {
+      int signaled = waiter.Wait();
+      ++shared_data_[signaled];
+      (*synchronizers_)[signaled]->Signal();
+    }
+  }
+
+ private:
+  size_t* shared_data_;
+  size_t repeats_;
+  const SharedMemSynchronizer::SynchronizerVector* synchronizers_;
+  size_t count_;
+  DISALLOW_COPY_AND_ASSIGN(MultiSynchronizerWorker);
+};
+
+// A fixed array of bool flags.  Each flag uses 1 bit.  Use sizeof(FlagArray)
+// to determine how much memory you need.  The number of flags will therefore
+// be sizeof(FlagArray) * 8.
+// We use 'struct' to signify that this structures represents compiler
+// independent structured data.  I.e. you must be able to map this class
+// to a piece of shared memory of size sizeof(FlagArray) and be able to
+// use the class.  No vtables etc.
+// TODO(tommi): Move this to its own header when we start using it for signaling
+// audio devices.  As is, it's just here for perf comparison against the
+// "multiple synchronizers" approach.
+struct FlagArray {
+ public:
+  FlagArray() : flags_() {}
+
+  bool is_set(size_t index) const {
+    return (flags_[index >> 5] & (1 << (index & 31))) ? true : false;
+  }
+
+  void set(size_t index) {
+    flags_[index >> 5] |= (1U << (static_cast<uint32>(index) & 31));
+  }
+
+  void clear(size_t index) {
+    flags_[index >> 5] &= ~(1U << (static_cast<uint32>(index) & 31));
+  }
+
+  // Returns the number of flags that can be set/checked.
+  size_t size() const { return sizeof(flags_) * 8; }
+
+ private:
+  // 256 * 32 = 8192 flags in 1KB.
+  uint32 flags_[256];
+  DISALLOW_COPY_AND_ASSIGN(FlagArray);
+};
+
+class MultiSynchronizerWorkerFlagArray : public base::PlatformThread::Delegate {
+ public:
+  MultiSynchronizerWorkerFlagArray(size_t count, FlagArray* signals,
+                         size_t* shared_data, size_t repeats,
+                         SharedMemSynchronizer* synchronizer)
+      : count_(count), signals_(signals), shared_data_(shared_data),
+        repeats_(repeats), synchronizer_(synchronizer) {
+  }
+  virtual ~MultiSynchronizerWorkerFlagArray() {}
+
+  virtual void ThreadMain() OVERRIDE {
+    for (size_t i = 0; i < repeats_; ++i) {
+      synchronizer_->Wait();
+      for (size_t s = 0; s < count_; ++s) {
+        if (signals_->is_set(s)) {
+          ++shared_data_[s];
+          // We don't clear the flag here but simply leave it signaled because
+          // we want the other thread to also increment this variable.
+        }
+      }
+      synchronizer_->Signal();
+    }
+  }
+
+ private:
+  size_t count_;
+  FlagArray* signals_;
+  size_t* shared_data_;
+  size_t repeats_;
+  SharedMemSynchronizer* synchronizer_;
+  DISALLOW_COPY_AND_ASSIGN(MultiSynchronizerWorkerFlagArray);
+};
+
+}  // end namespace
+
+TEST(SharedMemSynchronizer, FlagArray) {
+  FlagArray flags;
+  EXPECT_GT(flags.size(), 1000U);
+  for (size_t i = 0; i < flags.size(); ++i) {
+    EXPECT_FALSE(flags.is_set(i));
+    flags.set(i);
+    EXPECT_TRUE(flags.is_set(i));
+    flags.clear(i);
+    EXPECT_FALSE(flags.is_set(i));
+  }
+}
+
+// Initializes two synchronizers, signals the each one and make sure the others
+// wait is satisfied.
+TEST(SharedMemSynchronizer, Basic) {
+  SharedMemSynchronizer a, b;
+  ASSERT_TRUE(SharedMemSynchronizer::InitializePair(&a, &b));
+  EXPECT_TRUE(a.IsValid());
+  EXPECT_TRUE(b.IsValid());
+
+  a.Signal();
+  b.Wait();
+
+  b.Signal();
+  a.Wait();
+}
+
+// Spins two worker threads, each with their own SharedMemSynchronizer that they
+// use to read and write from a shared memory buffer.
+TEST(SharedMemSynchronizer, TwoThreads) {
+  SharedMemSynchronizer a, b;
+  ASSERT_TRUE(SharedMemSynchronizer::InitializePair(&a, &b));
+
+  size_t data = 0;
+  const size_t kRepeats = 10000;
+  SingleSynchronizerWorker worker_1(&data, kRepeats, &a);
+  SingleSynchronizerWorker worker_2(&data, kRepeats, &b);
+  base::PlatformThreadHandle thread_1, thread_2;
+  base::PlatformThread::Create(0, &worker_1, &thread_1);
+  base::PlatformThread::Create(0, &worker_2, &thread_2);
+
+  // Start the first thread.  They should ping pong a few times and take turns
+  // incrementing the shared variable and never step on each other's toes.
+  a.Signal();
+
+  base::PlatformThread::Join(thread_1);
+  base::PlatformThread::Join(thread_2);
+
+  EXPECT_EQ(kRepeats * 2, data);
+}
+
+// Uses a pair of threads to access up to 1000 pieces of synchronized shared
+// data. On regular dev machines, the number of synchronizers should be 1000,
+// but on mac and linux bots, the number will be smaller due to the
+// RLIMIT_NOFILE limit.  Specifically, linux will have this limit at 1024 which
+// means for this test that the max number of synchronizers will be in the
+// range 500-512.  On Mac the limit is 256, so |count| will be ~120.  Oh, and
+// raising the limit via setrlimit() won't work.
+TEST(SharedMemSynchronizer, ThousandSynchronizersTwoThreads) {
+  const size_t kCount = 1000;
+  SharedMemSynchronizer a[kCount], b[kCount];
+  size_t count = 0;
+  for (size_t i = 0; i < kCount; ++i) {
+    if (!SharedMemSynchronizer::InitializePair(&a[i], &b[i])) {
+      LOG(WARNING) << "SharedMemSynchronizer::InitializePair failed at " << i;
+      break;
+    }
+    ++count;
+  }
+
+  size_t data[kCount] = {0};
+  // We use a multiple of the count so that the division in the check below
+  // will be nice and round.
+  size_t repeats = count * 1;
+
+  SharedMemSynchronizer::SynchronizerVector a_vector, b_vector;
+  PopulateVectorFromStackArray(&a_vector, &a[0], count);
+  PopulateVectorFromStackArray(&b_vector, &b[0], count);
+
+  MultiSynchronizerWorker worker_1(&data[0], repeats, &a_vector);
+  MultiSynchronizerWorker worker_2(&data[0], repeats, &b_vector);
+  base::PlatformThreadHandle thread_1, thread_2;
+  base::PlatformThread::Create(0, &worker_1, &thread_1);
+  base::PlatformThread::Create(0, &worker_2, &thread_2);
+
+  for (size_t i = 0; i < count; ++i)
+    a[i].Signal();
+
+  base::PlatformThread::Join(thread_1);
+  base::PlatformThread::Join(thread_2);
+
+  size_t expected_total = count * 2;
+  size_t total = 0;
+  for (size_t i = 0; i < count; ++i) {
+    // The SharedMemSynchronizer::WaitForMultiple class should have ensured that
+    // all synchronizers had the same quality of service.
+    EXPECT_EQ(expected_total / count, data[i]);
+    total += data[i];
+  }
+  EXPECT_EQ(expected_total, total);
+}
+
+// Functionally equivalent (as far as the shared data goes) to the
+// ThousandSynchronizersTwoThreads test but uses a single pair of
+// synchronizers + FlagArray for the 1000 signals.
+// This approach is significantly faster.
+TEST(SharedMemSynchronizer, TwoSynchronizersTwoThreads1000Signals) {
+  SharedMemSynchronizer a, b;
+  ASSERT_TRUE(SharedMemSynchronizer::InitializePair(&a, &b));
+
+  const size_t kCount = 1000;
+  FlagArray signals;
+  ASSERT_GE(signals.size(), kCount);
+  size_t data[kCount] = {0};
+
+  // Since this algorithm checks all events each time the synchronizer is
+  // signaled, |repeat| doesn't mean the same thing here as it does in
+  // ThousandsynchronizersTwoThreads.  1 repeat here is the same as kCount
+  // repeats in ThousandsynchronizersTwoThreads.
+  size_t repeats = 1;
+  MultiSynchronizerWorkerFlagArray worker_1(
+      kCount, &signals, &data[0], repeats, &a);
+  MultiSynchronizerWorkerFlagArray worker_2(
+      kCount, &signals, &data[0], repeats, &b);
+  base::PlatformThreadHandle thread_1, thread_2;
+  base::PlatformThread::Create(0, &worker_1, &thread_1);
+  base::PlatformThread::Create(0, &worker_2, &thread_2);
+
+  for (size_t i = 0; i < kCount; ++i)
+    signals.set(i);
+  a.Signal();
+
+  base::PlatformThread::Join(thread_1);
+  base::PlatformThread::Join(thread_2);
+
+  size_t expected_total = kCount * 2;
+  size_t total = 0;
+  for (size_t i = 0; i < kCount; ++i) {
+    // Since for each signal, we process all signaled events, the shared data
+    // variables should all be equal.
+    EXPECT_EQ(expected_total / kCount, data[i]);
+    total += data[i];
+  }
+  EXPECT_EQ(expected_total, total);
+}
+
+// Test the maximum number of synchronizers without spinning further wait
+// threads on Windows. This test assumes we can always create 64 pairs and
+// bails if we can't.
+TEST(SharedMemSynchronizer, MultipleWaits64) {
+  const size_t kCount = 64;
+  SharedMemSynchronizer a[kCount], b[kCount];
+  for (size_t i = 0; i < kCount; ++i) {
+    ASSERT_TRUE(SharedMemSynchronizer::InitializePair(&a[i], &b[i]));
+  }
+
+  SharedMemSynchronizer::SynchronizerVector b_vector;
+  PopulateVectorFromStackArray(&b_vector, &b[0], kCount);
+  SharedMemSynchronizer::WaitForMultiple waiter(&b_vector);
+  for (size_t i = 0; i < kCount; ++i) {
+    a[i].Signal();
+    int index = waiter.Wait();
+    EXPECT_EQ(i, static_cast<size_t>(index));
+  }
+}
+
+// Tests waiting for more synchronizers than the OS supports on one thread.
+// The test will create at most 1000 pairs, but on mac/linux bots the actual
+// number will be lower.  See comment about the RLIMIT_NOFILE limit above for
+// more details.
+TEST(SharedMemSynchronizer, MultipleWaits1000) {
+  // A 1000 synchronizers requires 16 threads on Windows, including the current
+  // one, to perform the wait operation.
+  const size_t kCount = 1000;
+  SharedMemSynchronizer a[kCount], b[kCount];
+  size_t count = 0;
+  for (size_t i = 0; i < kCount; ++i) {
+    if (!SharedMemSynchronizer::InitializePair(&a[i], &b[i])) {
+      LOG(WARNING) << "SharedMemSynchronizer::InitializePair failed at " << i;
+      break;
+    }
+    ++count;
+  }
+
+  SharedMemSynchronizer::SynchronizerVector b_vector;
+  PopulateVectorFromStackArray(&b_vector, &b[0], count);
+
+  for (size_t i = 0; i < count; ++i) {
+    a[i].Signal();
+    // To disable the load distribution algorithm and force the extra worker
+    // thread(s) to catch the signaled event, we define the |waiter| inside
+    // the loop.
+    SharedMemSynchronizer::WaitForMultiple waiter(&b_vector);
+    int index = waiter.Wait();
+    EXPECT_EQ(i, static_cast<size_t>(index));
+  }
+}
+
+class SharedMemSynchronizerMultiProcessTest : public base::MultiProcessTest {
+ public:
+  static const char kSharedMemName[];
+  static const size_t kSharedMemSize = 1024;
+
+ protected:
+  virtual void SetUp() OVERRIDE {
+    base::MultiProcessTest::SetUp();
+  }
+
+  virtual void TearDown() OVERRIDE {
+    base::MultiProcessTest::TearDown();
+  }
+};
+
+// static
+const char SharedMemSynchronizerMultiProcessTest::kSharedMemName[] =
+    "SharedMemSynchronizerMultiProcessTest";
+
+namespace {
+// A very crude IPC mechanism that we use to set up the spawned child process
+// and the parent process.
+struct CrudeIpc {
+  uint8 ready;
+  SharedMemSynchronizer::IPCHandle handle_1;
+  SharedMemSynchronizer::IPCHandle handle_2;
+};
+}  // end namespace
+
+// The main routine of the child process.  Waits for the parent process
+// to copy handles over to the child and then uses a SharedMemSynchronizer to
+// wait and signal to the parent process.
+MULTIPROCESS_TEST_MAIN(SharedMemSynchronizerChildMain) {
+  base::SharedMemory mem;
+  bool ok = mem.CreateNamed(
+      SharedMemSynchronizerMultiProcessTest::kSharedMemName,
+      true,
+      SharedMemSynchronizerMultiProcessTest::kSharedMemSize);
+  DCHECK(ok);
+  if (!ok) {
+    LOG(ERROR) << "Failed to open shared memory segment.";
+    return -1;
+  }
+
+  mem.Map(SharedMemSynchronizerMultiProcessTest::kSharedMemSize);
+  CrudeIpc* ipc = reinterpret_cast<CrudeIpc*>(mem.memory());
+
+  while (!ipc->ready)
+    base::PlatformThread::Sleep(10);
+
+  SharedMemSynchronizer synchronizer(ipc->handle_1, ipc->handle_2);
+  synchronizer.Wait();
+  synchronizer.Signal();
+
+  return 0;
+}
+
+// Spawns a new process and hands a SharedMemSynchronizer instance to the
+// new process.  Once that's done, it waits for the child process to signal
+// it's end and quits.
+TEST_F(SharedMemSynchronizerMultiProcessTest, Basic) {
+  base::SharedMemory mem;
+  mem.Delete(kSharedMemName);  // In case a previous run was unsuccessful.
+  bool ok = mem.CreateNamed(kSharedMemName, false, kSharedMemSize);
+  ASSERT_TRUE(ok);
+
+  ASSERT_TRUE(mem.Map(kSharedMemSize));
+
+  SharedMemSynchronizer a, b;
+  ASSERT_TRUE(SharedMemSynchronizer::InitializePair(&a, &b));
+  EXPECT_TRUE(a.IsValid());
+  EXPECT_TRUE(b.IsValid());
+
+  CrudeIpc* ipc = reinterpret_cast<CrudeIpc*>(mem.memory());
+  ipc->ready = false;
+
+#if defined(OS_POSIX)
+  const int kPosixChildSocket = 20;
+  EXPECT_TRUE(b.ShareToProcess(NULL, &ipc->handle_1, &ipc->handle_2));
+  base::FileHandleMappingVector fd_mapping_vec;
+  fd_mapping_vec.push_back(std::pair<int, int>(ipc->handle_1.fd,
+                                               kPosixChildSocket));
+  ipc->handle_1.fd = kPosixChildSocket;
+  base::ProcessHandle process = SpawnChild("SharedMemSynchronizerChildMain",
+                                           fd_mapping_vec, false);
+#else
+  base::ProcessHandle process = SpawnChild("SharedMemSynchronizerChildMain",
+                                           false);
+  EXPECT_TRUE(b.ShareToProcess(process, &ipc->handle_1, &ipc->handle_2));
+#endif
+
+  ipc->ready = true;
+
+  a.Signal();
+  a.Wait();
+
+  int exit_code = -1;
+  base::WaitForExitCode(process, &exit_code);
+  EXPECT_EQ(0, exit_code);
+}