Initial GetSample implementation.

src/sampler.cc

Index: src/sampler.cc
diff --git a/src/sampler.cc b/src/sampler.cc
index 0ed4b379626a9746038b6e05b1661cee522f4f1f..36bce177a79a6ab23aa10499936459cf090360e5 100644
--- a/src/sampler.cc
+++ b/src/sampler.cc
@@ -1,7 +1,6 @@
 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-

[alph, 2014/09/17 11:55:43]

plz revert.

 #include "src/sampler.h"
 
 #if V8_OS_POSIX && !V8_OS_CYGWIN
@@ -44,6 +43,7 @@
 
 #include "src/v8.h"
 
+#include "src/base/logging.h"
 #include "src/base/platform/platform.h"
 #include "src/cpu-profiler-inl.h"
 #include "src/flags.h"
@@ -269,8 +269,24 @@ class SimulatorHelper {
 
 class SignalHandler : public AllStatic {
  public:
-  static void SetUp() { if (!mutex_) mutex_ = new base::Mutex(); }
-  static void TearDown() { delete mutex_; }
+  static void SetUp() {
+    if (mutex_ != NULL && sampling_semaphore_ != NULL)
+      return;                   // Already setup

[alph, 2014/09/17 11:55:42]

no need for the comment.

+
+    ASSERT_EQ(NULL, mutex_);
+    ASSERT_EQ(NULL, sampling_semaphore_);
+
+    mutex_ = new base::Mutex();
+    sampling_semaphore_ = new base::Semaphore(0);
+  }
+
+  static void TearDown() {
+    delete mutex_;
+    delete sampling_semaphore_;
+
+    mutex_ = NULL;
+    sampling_semaphore_ = NULL;
+  }
 
   static void IncreaseSamplerCount() {
     base::LockGuard<base::Mutex> lock_guard(mutex_);
@@ -308,14 +324,45 @@ class SignalHandler : public AllStatic {
   }
 
   static void HandleProfilerSignal(int signal, siginfo_t* info, void* context);
+
+  // The SIGPROF could have come from DoSample or from GetSample.
+  // GetSample is the internal endpoint for the public
+  // GetSample API, which aims to bypass all the internal buffers
+  // and return just one sample instead, rightaway.
+  //
+  // The origin of SIGPROF is determined by FLAG_new_sampler_api
+  //
+  // TODO(gholap): Eventually, get rid of DoSample.
+  //               Only GetSample should remain.
+  //               Then, get rid of FLAG_new_sampler_api too.
+
+  // This is the sample which will be filled by the call from GetSample.
+  static TickSample sample_;
+
+  // GetSample waits synchronously till the SIGPROF handler returns.
+  // this semaphore is used to signal GetSample.
+  static base::Semaphore* sampling_semaphore_;
+
+  // It is not that every time HandleProfilerSignal is invoked,
+  // it succeeds in obtaining a sample.
+  // This provides GetSample with the information whether
+  // the handler finished with or without getting the sample.
+  static bool sample_available_;
+
   // Protects the process wide state below.
   static base::Mutex* mutex_;
   static int client_count_;
   static bool signal_handler_installed_;
   static struct sigaction old_signal_handler_;
+
+  friend class Sampler;
 };
 
 
+TickSample SignalHandler::sample_;
+base::Semaphore* SignalHandler::sampling_semaphore_ = NULL;
+bool SignalHandler::sample_available_ = false;
+
 base::Mutex* SignalHandler::mutex_ = NULL;
 int SignalHandler::client_count_ = 0;
 struct sigaction SignalHandler::old_signal_handler_;
@@ -329,6 +376,11 @@ void SignalHandler::HandleProfilerSignal(int signal, siginfo_t* info,
   // is disabled.
   return;
 #else
+  // Even if we return prematurely,
+  // we need to signal the sampling_semaphore_
+  sample_available_ = false;
+  ScopedSemaphore scoped_semaphore(sampling_semaphore_);
+
   USE(info);
   if (signal != SIGPROF) return;
   Isolate* isolate = Isolate::UncheckedReentrantCurrent();
@@ -466,7 +518,12 @@ void SignalHandler::HandleProfilerSignal(int signal, siginfo_t* info,
 #endif  // V8_HOST_ARCH_*
 #endif  // V8_OS_QNX
 #endif  // USE_SIMULATOR
-  sampler->SampleStack(state);
+  if (FLAG_new_sampler_api) {
+    sample_.Init(sampler->isolate(), state);
+    sample_available_ = true;
+  } else {
+    sampler->SampleStack(state);
+  }
 #endif  // V8_OS_NACL
 }
 
@@ -569,6 +626,7 @@ DISABLE_ASAN void TickSample::Init(Isolate* isolate,
   timestamp = base::TimeTicks::HighResolutionNow();
   pc = regs.pc;
   state = isolate->current_vm_state();
+  frames_count = 0;
 
   // Avoid collecting traces while doing GC.
   if (state == GC) return;
@@ -621,6 +679,16 @@ void Sampler::TearDown() {
 }
 
 
+void Sampler::SetUpForNewSamplingAPI() {
+#if defined(USE_SIGNALS)
+  SignalHandler::SetUp();
+  if (!SignalHandler::Installed())
+    SignalHandler::Install();
+#endif
+    // Nothing needs to be done for windows.
+}
+
+
 Sampler::Sampler(Isolate* isolate, int interval)
     : isolate_(isolate),
       interval_(interval),
@@ -693,8 +761,34 @@ void Sampler::DoSample() {
   pthread_kill(platform_data()->vm_tid(), SIGPROF);
 }
 
+
+void Sampler::GetSample(v8::Sample* sample) {
+  SignalHandler::sampling_semaphore_->Wait();
+  if (SignalHandler::sample_available_) {
+    sample = new(sample) v8::Sample(
+      &SignalHandler::sample_.stack[0],
+      &SignalHandler::sample_.stack[SignalHandler::sample_.frames_count]);
+  }
+  else {
+    sample = new(sample) v8::Sample();
+  }
+}
+
 #elif V8_OS_WIN || V8_OS_CYGWIN
 
+#if V8_HOST_ARCH_X64
+#define CONTEXT_TO_STATE(context, state)             \
+  state.pc = reinterpret_cast<Address>(context.Rip); \
+  state.sp = reinterpret_cast<Address>(context.Rsp); \
+  state.fp = reinterpret_cast<Address>(context.Rbp)
+#else
+#define CONTEXT_TO_STATE(context, state)             \
+  state.pc = reinterpret_cast<Address>(context.Eip); \
+  state.sp = reinterpret_cast<Address>(context.Esp); \
+  state.fp = reinterpret_cast<Address>(context.Ebp)
+#endif
+
+
 void Sampler::DoSample() {
   HANDLE profiled_thread = platform_data()->profiled_thread();
   if (profiled_thread == NULL) return;
@@ -716,21 +810,25 @@ void Sampler::DoSample() {
 #if defined(USE_SIMULATOR)
     helper.FillRegisters(&state);
 #else
-#if V8_HOST_ARCH_X64
-    state.pc = reinterpret_cast<Address>(context.Rip);
-    state.sp = reinterpret_cast<Address>(context.Rsp);
-    state.fp = reinterpret_cast<Address>(context.Rbp);
-#else
-    state.pc = reinterpret_cast<Address>(context.Eip);
-    state.sp = reinterpret_cast<Address>(context.Esp);
-    state.fp = reinterpret_cast<Address>(context.Ebp);
-#endif
+    CONTEXT_TO_STATE(context, state);
 #endif  // USE_SIMULATOR
     SampleStack(state);
   }
   ResumeThread(profiled_thread);
 }
 
+
+void Sampler::GetSample(Isolate* isolate,
+                        const CONTEXT& context,
+                        v8::Sample* sample) {
+  TickSample tick_sample;
+  RegisterState state;
+  CONTEXT_TO_STATE(context, state);
+  tick_sample.Init(isolate, state);
+  sample = new(sample) v8::Sample(&tick_sample.stack[0],
+                                  &tick_sample.stack[tick_sample.frames_count]);
+}
+
 #endif  // USE_SIGNALS