Support parallel captures from the StackSamplingProfiler.

base/profiler/stack_sampling_profiler_unittest.cc

 // Copyright 2015 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 <stddef.h>
 #include <stdint.h>
 
 #include <cstdlib>
 #include <memory>
 #include <utility>
@@ skipping 333 matching lines @@
   target_thread.SignalThreadToFinish();
 
   PlatformThread::Join(target_thread_handle);
 }
 
 template <class Function>
 void WithTargetThread(Function function) {
   WithTargetThread(function, StackConfiguration(StackConfiguration::NORMAL));
 }
 
+// Waits for one of multiple samplings to complete.
+void CreateProfilers(
+    PlatformThreadId target_thread_id,
+    const std::vector<SamplingParams>& params,
+    std::vector<CallStackProfiles>* profiles,
+    std::vector<std::unique_ptr<StackSamplingProfiler>>* profilers,
+    std::vector<std::unique_ptr<WaitableEvent>>* completed) {
+  ASSERT_TRUE(!params.empty());
+  ASSERT_TRUE(profiles->empty());
+  ASSERT_TRUE(profilers->empty());
+  ASSERT_TRUE(completed->empty());
+
+  // Vectors have to be appropriately sized in advance so that the addresses of
+  // values don't change.
+  const size_t count = params.size();
+  profiles->reserve(count);
+  profilers->reserve(count);
+  completed->reserve(count);
+
+  for (size_t i = 0; i < count; ++i) {
+    profiles->push_back(CallStackProfiles());
+    completed->push_back(
+        MakeUnique<WaitableEvent>(WaitableEvent::ResetPolicy::AUTOMATIC,
+                                  WaitableEvent::InitialState::NOT_SIGNALED));
+    const StackSamplingProfiler::CompletedCallback callback =
+        Bind(&SaveProfilesAndSignalEvent, Unretained(&profiles->back()),
+             Unretained(completed->back().get()));
+    profilers->push_back(MakeUnique<StackSamplingProfiler>(
+        target_thread_id, params[i], callback));
+  }
+}
+
 // Captures profiles as specified by |params| on the TargetThread, and returns
 // them in |profiles|. Waits up to |profiler_wait_time| for the profiler to
 // complete.
 void CaptureProfiles(const SamplingParams& params, TimeDelta profiler_wait_time,
                      CallStackProfiles* profiles) {
   profiles->clear();
 
   WithTargetThread([&params, profiles,
                     profiler_wait_time](PlatformThreadId target_thread_id) {
     WaitableEvent sampling_thread_completed(
         WaitableEvent::ResetPolicy::MANUAL,
         WaitableEvent::InitialState::NOT_SIGNALED);
     const StackSamplingProfiler::CompletedCallback callback =
         Bind(&SaveProfilesAndSignalEvent, Unretained(profiles),
              Unretained(&sampling_thread_completed));
     StackSamplingProfiler profiler(target_thread_id, params, callback);
     profiler.Start();
     sampling_thread_completed.TimedWait(profiler_wait_time);
     profiler.Stop();
     sampling_thread_completed.Wait();
   });
 }
 
+// Waits for one of multiple samplings to complete.
+size_t WaitForSamplingComplete(
+    std::vector<std::unique_ptr<WaitableEvent>>* sampling_completed) {
+  // Map unique_ptrs to something that WaitMany can accept.
+  std::vector<WaitableEvent*> sampling_completed_rawptrs(
+      sampling_completed->size());
+  std::transform(
+      sampling_completed->begin(), sampling_completed->end(),
+      sampling_completed_rawptrs.begin(),
+      [](const std::unique_ptr<WaitableEvent>& elem) { return elem.get(); });
+  // Wait for one profiler to finish.
+  return WaitableEvent::WaitMany(sampling_completed_rawptrs.data(),
+                                 sampling_completed_rawptrs.size());
+}
+
 // If this executable was linked with /INCREMENTAL (the default for non-official
 // debug and release builds on Windows), function addresses do not correspond to
 // function code itself, but instead to instructions in the Incremental Link
 // Table that jump to the functions. Checks for a jump instruction and if
 // present does a little decompilation to find the function's actual starting
 // address.
 const void* MaybeFixupFunctionAddressForILT(const void* function_address) {
 #if defined(_WIN64)
   const unsigned char* opcode =
       reinterpret_cast<const unsigned char*>(function_address);
@@ skipping 50 matching lines @@
 // asynchronous library loading has completed before walking the stack. If
 // false, the unloading may still be occurring during the stack walk.
 void TestLibraryUnload(bool wait_until_unloaded) {
   // Test delegate that supports intervening between the copying of the stack
   // and the walking of the stack.
   class StackCopiedSignaler : public NativeStackSamplerTestDelegate {
    public:
     StackCopiedSignaler(WaitableEvent* stack_copied,
                         WaitableEvent* start_stack_walk,
                         bool wait_to_walk_stack)
-        : stack_copied_(stack_copied), start_stack_walk_(start_stack_walk),
-          wait_to_walk_stack_(wait_to_walk_stack) {
-    }
+        : stack_copied_(stack_copied),
+          start_stack_walk_(start_stack_walk),
+          wait_to_walk_stack_(wait_to_walk_stack) {}
 
     void OnPreStackWalk() override {
       stack_copied_->Signal();
       if (wait_to_walk_stack_)
         start_stack_walk_->Wait();
     }
 
    private:
     WaitableEvent* const stack_copied_;
     WaitableEvent* const start_stack_walk_;
@@ skipping 253 matching lines @@
              reinterpret_cast<const void*>(&TargetThread::CallWithAlloca))
       << " was not found in stack:\n"
       << FormatSampleForDiagnosticOutput(sample, profile.modules);
 
   // These frames should be adjacent on the stack.
   EXPECT_EQ(1, alloca_frame - end_frame)
       << "Stack:\n"
       << FormatSampleForDiagnosticOutput(sample, profile.modules);
 }
 
-// Checks that the fire-and-forget interface works.
-#if defined(STACK_SAMPLING_PROFILER_SUPPORTED)
-#define MAYBE_StartAndRunAsync StartAndRunAsync
-#else
-#define MAYBE_StartAndRunAsync DISABLED_StartAndRunAsync
-#endif
-TEST(StackSamplingProfilerTest, MAYBE_StartAndRunAsync) {
-  // StartAndRunAsync requires the caller to have a message loop.
-  MessageLoop message_loop;
-
-  SamplingParams params;
-  params.samples_per_burst = 1;
-
-  CallStackProfiles profiles;
-  WithTargetThread([&params, &profiles](PlatformThreadId target_thread_id) {
-    WaitableEvent sampling_thread_completed(
-        WaitableEvent::ResetPolicy::AUTOMATIC,
-        WaitableEvent::InitialState::NOT_SIGNALED);
-    const StackSamplingProfiler::CompletedCallback callback =
-        Bind(&SaveProfilesAndSignalEvent, Unretained(&profiles),
-             Unretained(&sampling_thread_completed));
-    StackSamplingProfiler::StartAndRunAsync(target_thread_id, params, callback);
-    RunLoop().RunUntilIdle();
-    sampling_thread_completed.Wait();
-  });
-
-  ASSERT_EQ(1u, profiles.size());
-}
-
 // Checks that the expected number of profiles and samples are present in the
 // call stack profiles produced.
 #if defined(STACK_SAMPLING_PROFILER_SUPPORTED)
 #define MAYBE_MultipleProfilesAndSamples MultipleProfilesAndSamples
 #else
 #define MAYBE_MultipleProfilesAndSamples DISABLED_MultipleProfilesAndSamples
 #endif
 TEST(StackSamplingProfilerTest, MAYBE_MultipleProfilesAndSamples) {
   SamplingParams params;
   params.burst_interval = params.sampling_interval =
       TimeDelta::FromMilliseconds(0);
   params.bursts = 2;
   params.samples_per_burst = 3;
 
   std::vector<CallStackProfile> profiles;
   CaptureProfiles(params, AVeryLongTimeDelta(), &profiles);
 
   ASSERT_EQ(2u, profiles.size());
   EXPECT_EQ(3u, profiles[0].samples.size());
   EXPECT_EQ(3u, profiles[1].samples.size());
 }
 
+// Checks that a profiler can stop/destruct without ever having started.
+#if defined(STACK_SAMPLING_PROFILER_SUPPORTED)
+#define MAYBE_StopWithoutStarting StopWithoutStarting
+#else
+#define MAYBE_StopWithoutStarting DISABLED_StopWithoutStarting
+#endif
+TEST(StackSamplingProfilerTest, MAYBE_StopWithoutStarting) {
+  WithTargetThread([](PlatformThreadId target_thread_id) {
+    SamplingParams params;
+    params.sampling_interval = TimeDelta::FromMilliseconds(0);
+    params.samples_per_burst = 1;
+
+    CallStackProfiles profiles;
+    WaitableEvent sampling_completed(WaitableEvent::ResetPolicy::MANUAL,
+                                     WaitableEvent::InitialState::NOT_SIGNALED);
+    const StackSamplingProfiler::CompletedCallback callback =
+        Bind(&SaveProfilesAndSignalEvent, Unretained(&profiles),
+             Unretained(&sampling_completed));
+    StackSamplingProfiler profiler(target_thread_id, params, callback);
+
+    profiler.Stop();  // Constructed but never started.
+    EXPECT_FALSE(sampling_completed.IsSignaled());
+  });
+}
+
 // Checks that no call stack profiles are captured if the profiling is stopped
 // during the initial delay.
 #if defined(STACK_SAMPLING_PROFILER_SUPPORTED)
 #define MAYBE_StopDuringInitialDelay StopDuringInitialDelay
 #else
 #define MAYBE_StopDuringInitialDelay DISABLED_StopDuringInitialDelay
 #endif
 TEST(StackSamplingProfilerTest, MAYBE_StopDuringInitialDelay) {
   SamplingParams params;
   params.initial_delay = TimeDelta::FromSeconds(60);
@@ skipping 69 matching lines @@
   });
 }
 
 // Checks that the same profiler may be run multiple times.
 #if defined(STACK_SAMPLING_PROFILER_SUPPORTED)
 #define MAYBE_CanRunMultipleTimes CanRunMultipleTimes
 #else
 #define MAYBE_CanRunMultipleTimes DISABLED_CanRunMultipleTimes
 #endif
 TEST(StackSamplingProfilerTest, MAYBE_CanRunMultipleTimes) {
+  StackSamplingProfiler::TestAPI::DisableIdleShutdown();
+
+  WithTargetThread([](PlatformThreadId target_thread_id) {
+    SamplingParams params;
+    params.sampling_interval = TimeDelta::FromMilliseconds(0);
+    params.samples_per_burst = 1;
+
+    CallStackProfiles profiles;
+    WaitableEvent sampling_completed(WaitableEvent::ResetPolicy::MANUAL,
+                                     WaitableEvent::InitialState::NOT_SIGNALED);
+    const StackSamplingProfiler::CompletedCallback callback =
+        Bind(&SaveProfilesAndSignalEvent, Unretained(&profiles),
+             Unretained(&sampling_completed));
+    StackSamplingProfiler profiler(target_thread_id, params, callback);
+
+    // Just start and stop to execute code paths.
+    profiler.Start();
+    profiler.Stop();
+    sampling_completed.Wait();
+
+    // Ensure a second request will run and not block.
+    sampling_completed.Reset();
+    profiles.clear();
+    profiler.Start();
+    sampling_completed.Wait();
+    profiler.Stop();
+    ASSERT_EQ(1u, profiles.size());
+  });
+}
+
+// Checks that the different profilers may be run.
+#if defined(STACK_SAMPLING_PROFILER_SUPPORTED)
+#define MAYBE_CanRunMultipleProfilers CanRunMultipleProfilers
+#else
+#define MAYBE_CanRunMultipleProfilers DISABLED_CanRunMultipleProfilers
+#endif
+TEST(StackSamplingProfilerTest, MAYBE_CanRunMultipleProfilers) {
+  StackSamplingProfiler::TestAPI::DisableIdleShutdown();
+
   SamplingParams params;
   params.sampling_interval = TimeDelta::FromMilliseconds(0);
   params.samples_per_burst = 1;
+
+  std::vector<CallStackProfile> profiles;
+  CaptureProfiles(params, AVeryLongTimeDelta(), &profiles);
+  ASSERT_EQ(1u, profiles.size());
+
+  profiles.clear();
+  CaptureProfiles(params, AVeryLongTimeDelta(), &profiles);
+  ASSERT_EQ(1u, profiles.size());
+}
+
+// Checks that the sampling thread can shut down.
+#if defined(STACK_SAMPLING_PROFILER_SUPPORTED)
+#define MAYBE_SamplerIdleShutdown SamplerIdleShutdown
+#else
+#define MAYBE_SamplerIdleShutdown DISABLED_SamplerIdleShutdown
+#endif
+TEST(StackSamplingProfilerTest, MAYBE_SamplerIdleShutdown) {
+  StackSamplingProfiler::TestAPI::DisableIdleShutdown();
+
+  SamplingParams params;
+  params.sampling_interval = TimeDelta::FromMilliseconds(0);
+  params.samples_per_burst = 1;
+
+  std::vector<CallStackProfile> profiles;
+  CaptureProfiles(params, AVeryLongTimeDelta(), &profiles);
+  ASSERT_EQ(1u, profiles.size());
+
+  // Capture thread should still be running at this point.
+  ASSERT_TRUE(StackSamplingProfiler::TestAPI::IsSamplingThreadRunning());
+
+  // Initiate an "idle" shutdown and ensure it happens. Idle-shutdown was
+  // disabled above so the test will fail due to a timeout if it does not
+  // exit.
+  StackSamplingProfiler::TestAPI::InitiateSamplingThreadIdleShutdown();
+  while (StackSamplingProfiler::TestAPI::IsSamplingThreadRunning())
+    PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(1));
+}
+
+// Checks that additional requests will restart a stopped profiler.
+#if defined(STACK_SAMPLING_PROFILER_SUPPORTED)
+#define MAYBE_WillRestartSamplerAfterIdleShutdown \
+  WillRestartSamplerAfterIdleShutdown
+#else
+#define MAYBE_WillRestartSamplerAfterIdleShutdown \
+  DISABLED_WillRestartSamplerAfterIdleShutdown
+#endif
+TEST(StackSamplingProfilerTest, MAYBE_WillRestartSamplerAfterIdleShutdown) {
+  StackSamplingProfiler::TestAPI::DisableIdleShutdown();
+
+  SamplingParams params;
+  params.sampling_interval = TimeDelta::FromMilliseconds(0);
+  params.samples_per_burst = 1;
 
   std::vector<CallStackProfile> profiles;
   CaptureProfiles(params, AVeryLongTimeDelta(), &profiles);
   ASSERT_EQ(1u, profiles.size());
 
+  // Capture thread should still be running at this point.
+  ASSERT_TRUE(StackSamplingProfiler::TestAPI::IsSamplingThreadRunning());
+
+  // Initiate an "idle" shutdown. Waiting for it to actually exit is the only
+  // way of knowing below that the thread "restarted".
+  StackSamplingProfiler::TestAPI::InitiateSamplingThreadIdleShutdown();
+  while (StackSamplingProfiler::TestAPI::IsSamplingThreadRunning())

[Mike Wittman, 2017/03/23 22:18:31]

Since the previous test has already established that the thread will eventually
exit, there's no need to reverify it here. The important behavior under test
here is simply that profiling can take place after idle shutdown has run.

[bcwhite, 2017/03/27 17:52:43]

It's not enough to know that it will exit.  It must have actually exited before
CaptureProfiles() below in order to know that it restarted and didn't just get
the idle-shutdown cancelled.

Without the IsSamplingThreadRunning() there is no way to know that the idle
shutdown has run let alone that the thread has exited. 
InitiateSamplingThreadIdleShutdown only posts a task that could be delayed by
any amount of time based on current activity and system load.

[Mike Wittman, 2017/03/28 19:32:02]

That's true. The explicit event for shutdown run rather than waiting on the
thread to exit is a clearer indication of what's happening regardless.

+    PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(1));
+
+  // Ensure another capture will start the sampling thread and run.
   profiles.clear();
   CaptureProfiles(params, AVeryLongTimeDelta(), &profiles);
   ASSERT_EQ(1u, profiles.size());
+  EXPECT_TRUE(StackSamplingProfiler::TestAPI::IsSamplingThreadRunning());
 }
 
-// Checks that requests to start profiling while another profile is taking place
-// are ignored.
+// Checks that it's safe to stop a task after it's completed and the sampling
+// thread has shut-down for being idle.
 #if defined(STACK_SAMPLING_PROFILER_SUPPORTED)
-#define MAYBE_ConcurrentProfiling ConcurrentProfiling
+#define MAYBE_StopAfterIdleShutdown StopAfterIdleShutdown
 #else
-#define MAYBE_ConcurrentProfiling DISABLED_ConcurrentProfiling
+#define MAYBE_StopAfterIdleShutdown DISABLED_StopAfterIdleShutdown
 #endif
-TEST(StackSamplingProfilerTest, MAYBE_ConcurrentProfiling) {
+TEST(StackSamplingProfilerTest, MAYBE_StopAfterIdleShutdown) {
+  StackSamplingProfiler::TestAPI::DisableIdleShutdown();
+
   WithTargetThread([](PlatformThreadId target_thread_id) {
-    SamplingParams params[2];
-    params[0].initial_delay = TimeDelta::FromMilliseconds(10);
-    params[0].sampling_interval = TimeDelta::FromMilliseconds(0);
-    params[0].samples_per_burst = 1;
+    SamplingParams params;
+    params.sampling_interval = TimeDelta::FromMilliseconds(0);
+    params.samples_per_burst = 1;
 
-    params[1].sampling_interval = TimeDelta::FromMilliseconds(0);
-    params[1].samples_per_burst = 1;
+    CallStackProfiles profiles;
+    WaitableEvent sampling_completed(WaitableEvent::ResetPolicy::MANUAL,
+                                     WaitableEvent::InitialState::NOT_SIGNALED);
+    const StackSamplingProfiler::CompletedCallback callback =
+        Bind(&SaveProfilesAndSignalEvent, Unretained(&profiles),
+             Unretained(&sampling_completed));
+    StackSamplingProfiler profiler(target_thread_id, params, callback);
 
-    CallStackProfiles profiles[2];
-    std::vector<std::unique_ptr<WaitableEvent>> sampling_completed(2);
-    std::vector<std::unique_ptr<StackSamplingProfiler>> profiler(2);
-    for (int i = 0; i < 2; ++i) {
-      sampling_completed[i] =
-          MakeUnique<WaitableEvent>(WaitableEvent::ResetPolicy::AUTOMATIC,
-                                    WaitableEvent::InitialState::NOT_SIGNALED);
-      const StackSamplingProfiler::CompletedCallback callback =
-          Bind(&SaveProfilesAndSignalEvent, Unretained(&profiles[i]),
-               Unretained(sampling_completed[i].get()));
-      profiler[i] = MakeUnique<StackSamplingProfiler>(target_thread_id,
-                                                      params[i], callback);
-    }
+    // Let it run and then stop due to being idle. The thread will go into the
+    // EXITING state (and remain there) sometime after the Initiate call posts
+    // its task and before the thread actually exits.

[Mike Wittman, 2017/03/23 22:18:31]

This is much better, although I think this information would be easier to
understand fleshed out more and applied to on the individual calls. Suggested
comments below.

[bcwhite, 2017/03/27 17:52:43]

Acknowledged.

+    profiler.Start();
+    sampling_completed.Wait();
+    StackSamplingProfiler::TestAPI::InitiateSamplingThreadIdleShutdown();

[Mike Wittman, 2017/03/23 22:18:31]

// Post a ShutdownTask on the sampling thread, which will mark the thread as
EXITING and shut down the thread asynchronously after the function exits.

[bcwhite, 2017/03/27 17:52:43]

Done.

+    while (StackSamplingProfiler::TestAPI::IsSamplingThreadRunning())

[Mike Wittman, 2017/03/23 22:18:31]

// Wait for the thread to exit to ensure the ShutdownTask has finished executing
and has set the thread state to EXITING.

[bcwhite, 2017/03/27 17:52:43]

Done.

+      PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(1));
 
-    profiler[0]->Start();
-    profiler[1]->Start();
-
-    std::vector<WaitableEvent*> sampling_completed_rawptrs(
-        sampling_completed.size());
-    std::transform(
-        sampling_completed.begin(), sampling_completed.end(),
-        sampling_completed_rawptrs.begin(),
-        [](const std::unique_ptr<WaitableEvent>& elem) { return elem.get(); });
-    // Wait for one profiler to finish.
-    size_t completed_profiler =
-        WaitableEvent::WaitMany(sampling_completed_rawptrs.data(), 2);
-    EXPECT_EQ(1u, profiles[completed_profiler].size());
-
-    size_t other_profiler = 1 - completed_profiler;
-    // Give the other profiler a chance to run and observe that it hasn't.
-    EXPECT_FALSE(sampling_completed[other_profiler]->TimedWait(
-        TimeDelta::FromMilliseconds(25)));
-
-    // Start the other profiler again and it should run.
-    profiler[other_profiler]->Start();
-    sampling_completed[other_profiler]->Wait();
-    EXPECT_EQ(1u, profiles[other_profiler].size());
+    // Ensure it's still safe to stop.

[Mike Wittman, 2017/03/23 22:18:31]

// Attempt to stop the profiler now that we know the thread is in the EXITING
state.

[bcwhite, 2017/03/27 17:52:43]

Done.

+    profiler.Stop();
+    EXPECT_FALSE(StackSamplingProfiler::TestAPI::IsSamplingThreadRunning());
   });
 }
 
+// Checks that synchronized multiple sampling requests execute in parallel.
+#if defined(STACK_SAMPLING_PROFILER_SUPPORTED)
+#define MAYBE_ConcurrentProfiling_InSync ConcurrentProfiling_InSync
+#else
+#define MAYBE_ConcurrentProfiling_InSync DISABLED_ConcurrentProfiling_InSync
+#endif
+TEST(StackSamplingProfilerTest, MAYBE_ConcurrentProfiling_InSync) {
+  StackSamplingProfiler::TestAPI::DisableIdleShutdown();
+
+  WithTargetThread([](PlatformThreadId target_thread_id) {
+    std::vector<SamplingParams> params(2);
+
+    // Providing an initial delay makes it more likely that both will be
+    // scheduled before either starts to run. Once started, samples will
+    // run ordered by their scheduled, interleaved times regardless of
+    // whatever interval the thread wakes up. Thus, total execution time
+    // will be 10ms (delay) + 10x1ms (sampling) + 1/2 timer minimum interval.
+    params[0].initial_delay = TimeDelta::FromMilliseconds(10);
+    params[0].sampling_interval = TimeDelta::FromMilliseconds(1);
+    params[0].samples_per_burst = 9;
+
+    params[1].initial_delay = TimeDelta::FromMilliseconds(11);
+    params[1].sampling_interval = TimeDelta::FromMilliseconds(1);
+    params[1].samples_per_burst = 8;
+
+    std::vector<CallStackProfiles> profiles;
+    std::vector<std::unique_ptr<StackSamplingProfiler>> profilers;
+    std::vector<std::unique_ptr<WaitableEvent>> sampling_completed;
+    CreateProfilers(target_thread_id, params, &profiles, &profilers,
+                    &sampling_completed);
+
+    profilers[0]->Start();
+    profilers[1]->Start();
+
+    // Wait for one profiler to finish.
+    size_t completed_profiler = WaitForSamplingComplete(&sampling_completed);
+    ASSERT_EQ(1u, profiles[completed_profiler].size());
+
+    size_t other_profiler = 1 - completed_profiler;
+    // Wait for the other profiler to finish.
+    sampling_completed[other_profiler]->Wait();
+    ASSERT_EQ(1u, profiles[other_profiler].size());
+
+    // Ensure each got the correct number of samples.
+    EXPECT_EQ(9u, profiles[0][0].samples.size());
+    EXPECT_EQ(8u, profiles[1][0].samples.size());
+  });
+}
+
+// Checks that several mixed sampling requests execute in parallel.
+#if defined(STACK_SAMPLING_PROFILER_SUPPORTED)
+#define MAYBE_ConcurrentProfiling_Mixed ConcurrentProfiling_Mixed
+#else
+#define MAYBE_ConcurrentProfiling_Mixed DISABLED_ConcurrentProfiling_Mixed
+#endif
+TEST(StackSamplingProfilerTest, MAYBE_ConcurrentProfiling_Mixed) {
+  StackSamplingProfiler::TestAPI::DisableIdleShutdown();
+
+  WithTargetThread([](PlatformThreadId target_thread_id) {
+    std::vector<SamplingParams> params(3);
+
+    params[0].initial_delay = TimeDelta::FromMilliseconds(8);
+    params[0].sampling_interval = TimeDelta::FromMilliseconds(4);
+    params[0].samples_per_burst = 10;
+
+    params[1].initial_delay = TimeDelta::FromMilliseconds(9);
+    params[1].sampling_interval = TimeDelta::FromMilliseconds(3);
+    params[1].samples_per_burst = 10;
+
+    params[2].initial_delay = TimeDelta::FromMilliseconds(10);
+    params[2].sampling_interval = TimeDelta::FromMilliseconds(2);
+    params[2].samples_per_burst = 10;
+
+    std::vector<CallStackProfiles> profiles;
+    std::vector<std::unique_ptr<StackSamplingProfiler>> profilers;
+    std::vector<std::unique_ptr<WaitableEvent>> sampling_completed;
+    CreateProfilers(target_thread_id, params, &profiles, &profilers,
+                    &sampling_completed);
+
+    for (size_t i = 0; i < profilers.size(); ++i)
+      profilers[i]->Start();
+
+    // Wait for one profiler to finish.
+    size_t completed_profiler = WaitForSamplingComplete(&sampling_completed);
+    EXPECT_EQ(1u, profiles[completed_profiler].size());
+    // Stop and destroy all profilers, always in the same order. Don't crash.
+    for (size_t i = 0; i < profilers.size(); ++i)
+      profilers[i]->Stop();
+    for (size_t i = 0; i < profilers.size(); ++i)
+      profilers[i].reset();
+  });
+}
+
+// Checks that sampling requests execute in a staggered manner.
+#if defined(STACK_SAMPLING_PROFILER_SUPPORTED)
+#define MAYBE_ConcurrentProfiling_Staggered ConcurrentProfiling_Staggered
+#else
+#define MAYBE_ConcurrentProfiling_Staggered \
+  DISABLED_ConcurrentProfiling_Staggered
+#endif
+TEST(StackSamplingProfilerTest, MAYBE_ConcurrentProfiling_Staggered) {
+  StackSamplingProfiler::TestAPI::DisableIdleShutdown();
+
+  WithTargetThread([](PlatformThreadId target_thread_id) {
+    std::vector<SamplingParams> params(3);
+
+    // Create an arbitrary variety of sampling parameters. The exact values of
+    // these are unimportant other than they should not run too long.
+    params[0].initial_delay = TimeDelta::FromMilliseconds(10);
+    params[0].sampling_interval = TimeDelta::FromMilliseconds(10);
+    params[0].samples_per_burst = 1;
+
+    params[1].initial_delay = TimeDelta::FromMilliseconds(5);
+    params[1].sampling_interval = TimeDelta::FromMilliseconds(10);
+    params[1].samples_per_burst = 2;
+
+    params[2].initial_delay = TimeDelta::FromMilliseconds(0);
+    params[2].sampling_interval = TimeDelta::FromMilliseconds(10);
+    params[2].samples_per_burst = 3;
+
+    std::vector<CallStackProfiles> profiles;
+    std::vector<std::unique_ptr<StackSamplingProfiler>> profilers;
+    std::vector<std::unique_ptr<WaitableEvent>> sampling_completed;
+    CreateProfilers(target_thread_id, params, &profiles, &profilers,
+                    &sampling_completed);
+
+    profilers[0]->Start();
+    profilers[1]->Start();
+    sampling_completed[0]->Wait();
+    profilers[0]->Stop();
+    profilers[2]->Start();
+    profilers[1]->Stop();
+    sampling_completed[1]->Wait();
+    sampling_completed[2]->Wait();
+    EXPECT_EQ(1u, profiles[0].size());
+    EXPECT_EQ(1u, profiles[1].size());
+    EXPECT_EQ(1u, profiles[2].size());
+  });
+}
+
 // Checks that a stack that runs through another library produces a stack with
 // the expected functions.
 #if defined(STACK_SAMPLING_PROFILER_SUPPORTED)
 #define MAYBE_OtherLibrary OtherLibrary
 #else
 #define MAYBE_OtherLibrary DISABLED_OtherLibrary
 #endif
 TEST(StackSamplingProfilerTest, MAYBE_OtherLibrary) {
   SamplingParams params;
   params.sampling_interval = TimeDelta::FromMilliseconds(0);
@@ skipping 74 matching lines @@
 #if defined(STACK_SAMPLING_PROFILER_SUPPORTED)
 #define MAYBE_UnloadedLibrary UnloadedLibrary
 #else
 #define MAYBE_UnloadedLibrary DISABLED_UnloadedLibrary
 #endif
 TEST(StackSamplingProfilerTest, MAYBE_UnloadedLibrary) {
   TestLibraryUnload(true);
 }
 
 }  // namespace base