Support parallel captures from the StackSamplingProfiler.

base/profiler/stack_sampling_profiler.h

 // 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.
 
 #ifndef BASE_PROFILER_STACK_SAMPLING_PROFILER_H_
 #define BASE_PROFILER_STACK_SAMPLING_PROFILER_H_
 
 #include <stddef.h>
 
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/atomicops.h"
 #include "base/base_export.h"
 #include "base/callback.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/platform_thread.h"
 #include "base/time/time.h"
 
 namespace base {
 
 class NativeStackSampler;
 class NativeStackSamplerTestDelegate;
+class WaitableEvent;
 
 // StackSamplingProfiler periodically stops a thread to sample its stack, for
 // the purpose of collecting information about which code paths are
 // executing. This information is used in aggregate by UMA to identify hot
 // and/or janky code paths.
 //
 // Sample StackSamplingProfiler usage:
 //
 //   // Create and customize params as desired.
 //   base::StackStackSamplingProfiler::SamplingParams params;
@@ skipping 137 matching lines @@
 
     // Number of samples to record per burst. Defaults to 300.
     int samples_per_burst;
 
     // Interval between samples during a sampling burst. This is the desired
     // duration from the start of one sample to the start of the next
     // sample. Defaults to 100ms.
     TimeDelta sampling_interval;
   };
 
+  // Testing support.
+  class BASE_EXPORT TestAPI {
+   public:
+    // Returns whether the sampling thread is currently running or not.
+    static bool IsSamplingThreadRunning();
+
+    // Sets the auto-shutdown delay time for the sampling thread, in ms. Set
+    // this to zero to disable it.
+    static void SetSamplingThreadIdleShutdownTime(int shutdown_ms);

[Mike Wittman, 2017/02/22 20:32:18]

This function is only ever used to disable the the idle shutdown, so we should
name it accordingly, e.g. DisableSamplingThreadIdleShutdown().

I can't see a test use for setting the shutdown time that wouldn't be better
served by explicit coordination using the TestDelegate.

[bcwhite, 2017/02/24 20:39:24]

Done.

+
+    // Initiates an idle shutdown task, as though the idle timer had expired,
+    // causing the thread to exit if there are no more sampling tasks pending.
+    // This returns immediately. Watch IsSamplingThreadRunningForTesting() to
+    // know when the thread has exited, though it will never do so if it is
+    // not idle.
+    static void InitiateSamplingThreadIdleShutdown();
+  };
+
   // The callback type used to collect completed profiles. The passed |profiles|
-  // are move-only.
+  // are move-only. Other threads, including the UI thread, may block on
+  // callback completion so this should run as quickly as possible.
   //
-  // IMPORTANT NOTE: the callback is invoked on a thread the profiler
+  // IMPORTANT NOTE: The callback is invoked on a thread the profiler
   // constructs, rather than on the thread used to construct the profiler and
   // set the callback, and thus the callback must be callable on any thread. For
   // threads with message loops that create StackSamplingProfilers, posting a
-  // task to the message loop with a copy of the profiles is the recommended
+  // task to the message loop with the moved (i.e. std::move) profiles is the
   // thread-safe callback implementation.
   using CompletedCallback = Callback<void(CallStackProfiles)>;
 
-  // Creates a profiler that sends completed profiles to |callback|. The second
-  // constructor is for test purposes.
-  StackSamplingProfiler(PlatformThreadId thread_id,
-                        const SamplingParams& params,
-                        const CompletedCallback& callback);
-  StackSamplingProfiler(PlatformThreadId thread_id,
-                        const SamplingParams& params,
-                        const CompletedCallback& callback,
-                        NativeStackSamplerTestDelegate* test_delegate);
+  // Creates a profiler for the CURRENT thread that sends completed profiles
+  // to |callback|. An optional |test_delegate| can be supplied by tests.
+  // The caller must ensure that this object gets destroyed before the current
+  // thread exits.
+  StackSamplingProfiler(
+      const SamplingParams& params,
+      const CompletedCallback& callback,
+      NativeStackSamplerTestDelegate* test_delegate = nullptr);
+
+  // Creates a profiler for ANOTHER thread that sends completed profiles to
+  // |callback|. An optional |test_delegate| can be supplied by tests.
+  //
+  // IMPORTANT: The caller must ensure that the thread being sampled does not
+  // exit before this object gets destructed or Bad Things(tm) may occur.
+  StackSamplingProfiler(
+      PlatformThreadId thread_id,
+      const SamplingParams& params,
+      const CompletedCallback& callback,
+      NativeStackSamplerTestDelegate* test_delegate = nullptr);
+
   // Stops any profiling currently taking place before destroying the profiler.
+  // This will block until the callback has been run.
   ~StackSamplingProfiler();
 
-  // The fire-and-forget interface: starts a profiler and allows it to complete
-  // without the caller needing to manage the profiler lifetime. May be invoked
-  // from any thread, but requires that the calling thread has a message loop.
-  static void StartAndRunAsync(PlatformThreadId thread_id,
-                               const SamplingParams& params,
-                               const CompletedCallback& callback);
-
   // Initializes the profiler and starts sampling.
   void Start();
 
-  // Stops the profiler and any ongoing sampling. Calling this function is
-  // optional; if not invoked profiling terminates when all the profiling bursts
-  // specified in the SamplingParams are completed or the profiler is destroyed,
-  // whichever occurs first.
+  // Stops the profiler and any ongoing sampling. This method will return
+  // immediately with the callback being run asynchronously. At most one
+  // more stack sample will be taken after this method returns. Calling this
+  // function is optional; if not invoked profiling terminates when all the
+  // profiling bursts specified in the SamplingParams are completed or the
+  // profiler object is destroyed, whichever occurs first.
   void Stop();
 
   // Set the current system state that is recorded with each captured stack
   // frame. This is thread-safe so can be called from anywhere. The parameter
   // value should be from an enumeration of the appropriate type with values
   // ranging from 0 to 31, inclusive. This sets bits within Sample field of
   // |process_milestones|. The actual meanings of these bits are defined
   // (globally) by the caller(s).
   static void SetProcessMilestone(int milestone);
   static void ResetAnnotationsForTesting();
 
  private:
+  friend class TestAPI;
+
   // SamplingThread is a separate thread used to suspend and sample stacks from
   // the target thread.
-  class SamplingThread : public PlatformThread::Delegate {
-   public:
-    // Samples stacks using |native_sampler|. When complete, invokes
-    // |completed_callback| with the collected call stack profiles.
-    // |completed_callback| must be callable on any thread.
-    SamplingThread(std::unique_ptr<NativeStackSampler> native_sampler,
-                   const SamplingParams& params,
-                   const CompletedCallback& completed_callback);
-    ~SamplingThread() override;
-
-    // PlatformThread::Delegate:
-    void ThreadMain() override;
-
-    void Stop();
-
-   private:
-    // Collects |profile| from a single burst. If the profiler was stopped
-    // during collection, sets |was_stopped| and provides the set of samples
-    // collected up to that point.
-    void CollectProfile(CallStackProfile* profile, TimeDelta* elapsed_time,
-                        bool* was_stopped);
-
-    // Collects call stack profiles from all bursts, or until the sampling is
-    // stopped. If stopped before complete, the last profile in
-    // |call_stack_profiles| may contain a partial burst.
-    void CollectProfiles(CallStackProfiles* profiles);
-
-    std::unique_ptr<NativeStackSampler> native_sampler_;
-    const SamplingParams params_;
-
-    // If Stop() is called, it signals this event to force the sampling to
-    // terminate before all the samples specified in |params_| are collected.
-    WaitableEvent stop_event_;
-
-    const CompletedCallback completed_callback_;
-
-    DISALLOW_COPY_AND_ASSIGN(SamplingThread);
-  };
+  class SamplingThread;
 
   // Adds annotations to a Sample.
   static void RecordAnnotations(Sample* sample);
 
   // This global variables holds the current system state and is recorded with
   // every captured sample, done on a separate thread which is why updates to
   // this must be atomic. A PostTask to move the the updates to that thread
   // would skew the timing and a lock could result in deadlock if the thread
   // making a change was also being profiled and got stopped.
   static subtle::Atomic32 process_milestones_;
 
   // The thread whose stack will be sampled.
   PlatformThreadId thread_id_;
 
   const SamplingParams params_;
 
-  std::unique_ptr<SamplingThread> sampling_thread_;
-  PlatformThreadHandle sampling_thread_handle_;
+  const CompletedCallback completed_callback_;
 
-  const CompletedCallback completed_callback_;
+  // An event signaled when all sampling is complete and the callback done.
+  WaitableEvent finished_event_;
+
+  // Object that does the native sampling. This is created during construction
+  // and later passed to the sampling thread when profiling is started.
+  std::unique_ptr<NativeStackSampler> native_sampler_;
+
+  // An ID uniquely identifying this collection to the sampling thread.

[Mike Wittman, 2017/02/22 20:32:18]

Also mention the conditions under which this will be null.

[bcwhite, 2017/02/24 20:39:24]

Done.

+  int collection_id_;
 
   // Stored until it can be passed to the NativeStackSampler created in Start().
   NativeStackSamplerTestDelegate* const test_delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(StackSamplingProfiler);
 };
 
 // These operators permit types to be compared and used in a map of Samples, as
 // done in tests and by the metrics provider code.
 BASE_EXPORT bool operator==(const StackSamplingProfiler::Module& a,
                             const StackSamplingProfiler::Module& b);
 BASE_EXPORT bool operator==(const StackSamplingProfiler::Sample& a,
                             const StackSamplingProfiler::Sample& b);
 BASE_EXPORT bool operator!=(const StackSamplingProfiler::Sample& a,
                             const StackSamplingProfiler::Sample& b);
 BASE_EXPORT bool operator<(const StackSamplingProfiler::Sample& a,
                            const StackSamplingProfiler::Sample& b);
 BASE_EXPORT bool operator==(const StackSamplingProfiler::Frame& a,
                             const StackSamplingProfiler::Frame& b);
 BASE_EXPORT bool operator<(const StackSamplingProfiler::Frame& a,
                            const StackSamplingProfiler::Frame& b);
 
 }  // namespace base
 
 #endif  // BASE_PROFILER_STACK_SAMPLING_PROFILER_H_