Initial GetSample implementation.

src/sampler.cc

Index: src/sampler.cc
diff --git a/src/sampler.cc b/src/sampler.cc
index 0ed4b379626a9746038b6e05b1661cee522f4f1f..c7e7c0f2b6723aed1d90d4e36d25feab12d8b991 100644
--- a/src/sampler.cc
+++ b/src/sampler.cc
@@ -42,6 +42,8 @@
 
 #endif
 
+#include "include/v8-sampler.h"
+
 #include "src/v8.h"
 
 #include "src/base/platform/platform.h"
@@ -269,8 +271,16 @@ 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_) mutex_ = new base::Mutex();
+    if (!register_state_semaphore_)
+      register_state_semaphore_ = new base::Semaphore(0);
+  }
+
+  static void TearDown() {
+    delete mutex_;
+    delete register_state_semaphore_;
+  }
 
   static void IncreaseSamplerCount() {
     base::LockGuard<base::Mutex> lock_guard(mutex_);
@@ -286,6 +296,17 @@ class SignalHandler : public AllStatic {
     return signal_handler_installed_;
   }
 
+  static RegisterState GetRegisterState() {
+    register_state_semaphore_->Wait();
+    register_state_updated_ = false;
+    return register_state_;
+  }
+
+  static bool WasRegisterStateUpdated() {
+    return register_state_updated_;
+  }
+
+
  private:
   static void Install() {
     struct sigaction sa;
@@ -308,6 +329,18 @@ class SignalHandler : public AllStatic {
   }
 
   static void HandleProfilerSignal(int signal, siginfo_t* info, void* context);
+
+  // HandleProfilerSignal puts the state of registers into
+  // register_state_ and then signals on the semaphore,
+  // so that DoSample can use it.
+  static base::Semaphore* register_state_semaphore_;
+  static RegisterState register_state_;
+  // It is not that every time HandleProfilerSignal is invoked,
+  // the register state is guarenteed to be updated.
+  // This provides the SIGPROF sender with the information whether
+  // the handler finished with or without updating the register state.
+  static bool register_state_updated_;
+
   // Protects the process wide state below.
   static base::Mutex* mutex_;
   static int client_count_;
@@ -321,6 +354,9 @@ int SignalHandler::client_count_ = 0;
 struct sigaction SignalHandler::old_signal_handler_;
 bool SignalHandler::signal_handler_installed_ = false;
 
+base::Semaphore* SignalHandler::register_state_semaphore_ = NULL;
+RegisterState SignalHandler::register_state_;
+bool SignalHandler::register_state_updated_ = false;
 
 void SignalHandler::HandleProfilerSignal(int signal, siginfo_t* info,
                                          void* context) {
@@ -466,7 +502,9 @@ void SignalHandler::HandleProfilerSignal(int signal, siginfo_t* info,
 #endif  // V8_HOST_ARCH_*
 #endif  // V8_OS_QNX
 #endif  // USE_SIMULATOR
-  sampler->SampleStack(state);
+  register_state_ = state;
+  register_state_updated_ = true;
+  register_state_semaphore_->Signal();
 #endif  // V8_OS_NACL
 }
 
@@ -564,7 +602,8 @@ SamplerThread* SamplerThread::instance_ = NULL;
 // StackTracer implementation
 //
 DISABLE_ASAN void TickSample::Init(Isolate* isolate,
-                                   const RegisterState& regs) {
+                                   const RegisterState& regs,
+                                   unsigned max_frame_count) {
   ASSERT(isolate->IsInitialized());
   timestamp = base::TimeTicks::HighResolutionNow();
   pc = regs.pc;
@@ -597,7 +636,9 @@ DISABLE_ASAN void TickSample::Init(Isolate* isolate,
   SafeStackFrameIterator it(isolate, regs.fp, regs.sp, js_entry_sp);
   top_frame_type = it.top_frame_type();
   unsigned i = 0;
-  while (!it.done() && i < TickSample::kMaxFramesCount) {
+  if (max_frame_count > kMaxFramesCount)
+    max_frame_count = kMaxFramesCount;
+  while (!it.done() && i < max_frame_count) {
     stack[i++] = it.frame()->pc();
     it.Advance();
   }
@@ -688,14 +729,33 @@ void Sampler::SampleStack(const RegisterState& state) {
 
 #if defined(USE_SIGNALS)
 
-void Sampler::DoSample() {
+void Sampler::CaptureRegisterState_() {
   if (!SignalHandler::Installed()) return;
   pthread_kill(platform_data()->vm_tid(), SIGPROF);
 }
 
-#elif V8_OS_WIN || V8_OS_CYGWIN
 
 void Sampler::DoSample() {
+  CaptureRegisterState_();
+  if (SignalHandler::WasRegisterStateUpdated())
+    SampleStack(SignalHandler::GetRegisterState());
+}
+
+
+void Sampler::GetSample(TickSample* sample, unsigned max_frame_count) {
+  CaptureRegisterState_();
+  if (SignalHandler::WasRegisterStateUpdated())
+    sample->Init(isolate_,
+                 SignalHandler::GetRegisterState(),
+                 max_frame_count);
+}
+
+#elif V8_OS_WIN || V8_OS_CYGWIN
+
+void Sampler::CaptureRegisterState_(RegisterState* state,
+                                    bool* captured_successfully) {
+  *captured_successfully = false;
+
   HANDLE profiled_thread = platform_data()->profiled_thread();
   if (profiled_thread == NULL) return;
 
@@ -712,25 +772,41 @@ void Sampler::DoSample() {
   memset(&context, 0, sizeof(context));
   context.ContextFlags = CONTEXT_FULL;
   if (GetThreadContext(profiled_thread, &context) != 0) {
-    RegisterState state;
 #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);
+    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);
+    state->pc = reinterpret_cast<Address>(context.Eip);
+    state->sp = reinterpret_cast<Address>(context.Esp);
+    state->fp = reinterpret_cast<Address>(context.Ebp);
 #endif
 #endif  // USE_SIMULATOR
-    SampleStack(state);
+    *captured_successfully = true;
   }
   ResumeThread(profiled_thread);
 }
 
+
+void Sampler::DoSample() {
+  bool register_state_captured;
+  RegisterState state;
+  CaptureRegisterState_(state, register_state_captured);
+  if (register_state_captured) SampleStack(state);
+}
+
+
+void Sampler::GetSample(TickSample* sample, unsigned max_frame_count) {
+  bool register_state_captured;
+  RegisterState state;
+  CaptureRegisterState_(state, register_state_captured);
+  if (register_state_captured)
+    sample->Init(isolate_, state, max_frame_count);
+}
+
 #endif  // USE_SIGNALS