Moving cpu profiling into its own thread.

src/platform-linux.cc

Index: src/platform-linux.cc
diff --git a/src/platform-linux.cc b/src/platform-linux.cc
index d02244896bcf8930ecd895a92a7b2ab5a5365b32..f023baba7a3e057fa49fbad10e1365f747187797 100644
--- a/src/platform-linux.cc
+++ b/src/platform-linux.cc
@@ -1055,6 +1055,37 @@ static void ProfilerSignalHandler(int signal, siginfo_t* info, void* context) {
 }
 
 
+class CpuProfilerSignalHandler {
+ public:
+  static void InstallSignalHandler() {
+    if (signal_handler_installed_) return;
+    struct sigaction sa;
+    sa.sa_sigaction = ProfilerSignalHandler;
+    sigemptyset(&sa.sa_mask);
+    sa.sa_flags = SA_RESTART | SA_SIGINFO;
+    signal_handler_installed_ =
+        (sigaction(SIGPROF, &sa, &old_signal_handler_) == 0);
+  }
+
+  static void RestoreSignalHandler() {
+    if (signal_handler_installed_) {
+      sigaction(SIGPROF, &old_signal_handler_, 0);
+      signal_handler_installed_ = false;
+    }
+  }
+
+  static bool signal_handler_installed() { return signal_handler_installed_; }
+
+ private:
+  static bool signal_handler_installed_;
+  static struct sigaction old_signal_handler_;
+};
+
+
+bool CpuProfilerSignalHandler::signal_handler_installed_ = false;
+struct sigaction CpuProfilerSignalHandler::old_signal_handler_;
+
+
 class Sampler::PlatformData : public Malloced {
  public:
   PlatformData() : vm_tid_(GetThreadID()) {}
@@ -1083,22 +1114,6 @@ class SignalSender : public Thread {
   static void SetUp() { if (!mutex_) mutex_ = OS::CreateMutex(); }
   static void TearDown() { delete mutex_; }
 
-  static void InstallSignalHandler() {
-    struct sigaction sa;
-    sa.sa_sigaction = ProfilerSignalHandler;
-    sigemptyset(&sa.sa_mask);
-    sa.sa_flags = SA_RESTART | SA_SIGINFO;
-    signal_handler_installed_ =
-        (sigaction(SIGPROF, &sa, &old_signal_handler_) == 0);
-  }
-
-  static void RestoreSignalHandler() {
-    if (signal_handler_installed_) {
-      sigaction(SIGPROF, &old_signal_handler_, 0);
-      signal_handler_installed_ = false;
-    }
-  }
-
   static void AddActiveSampler(Sampler* sampler) {
     ScopedLock lock(mutex_);
     SamplerRegistry::AddActiveSampler(sampler);
@@ -1119,7 +1134,6 @@ class SignalSender : public Thread {
       RuntimeProfiler::StopRuntimeProfilerThreadBeforeShutdown(instance_);
       delete instance_;
       instance_ = NULL;
-      RestoreSignalHandler();
     }
   }
 
@@ -1129,13 +1143,8 @@ class SignalSender : public Thread {
     while ((state = SamplerRegistry::GetState()) !=
            SamplerRegistry::HAS_NO_SAMPLERS) {
       bool cpu_profiling_enabled =
-          (state == SamplerRegistry::HAS_CPU_PROFILING_SAMPLERS);
+          (!FLAG_sample_stack_in_postprocessor_thread && state == SamplerRegistry::HAS_CPU_PROFILING_SAMPLERS);
       bool runtime_profiler_enabled = RuntimeProfiler::IsEnabled();
-      if (cpu_profiling_enabled && !signal_handler_installed_) {
-        InstallSignalHandler();
-      } else if (!cpu_profiling_enabled && signal_handler_installed_) {
-        RestoreSignalHandler();
-      }
       // When CPU profiling is enabled both JavaScript and C++ code is
       // profiled. We must not suspend.
       if (!cpu_profiling_enabled) {
@@ -1180,7 +1189,7 @@ class SignalSender : public Thread {
   }
 
   void SendProfilingSignal(int tid) {
-    if (!signal_handler_installed_) return;
+    if (!CpuProfilerSignalHandler::signal_handler_installed()) return;
     // Glibc doesn't provide a wrapper for tgkill(2).
 #if defined(ANDROID)
     syscall(__NR_tgkill, vm_tgid_, tid, SIGPROF);
@@ -1218,8 +1227,6 @@ class SignalSender : public Thread {
   // Protects the process wide state below.
   static Mutex* mutex_;
   static SignalSender* instance_;
-  static bool signal_handler_installed_;
-  static struct sigaction old_signal_handler_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SignalSender);
@@ -1228,8 +1235,6 @@ class SignalSender : public Thread {
 
 Mutex* SignalSender::mutex_ = NULL;
 SignalSender* SignalSender::instance_ = NULL;
-struct sigaction SignalSender::old_signal_handler_;
-bool SignalSender::signal_handler_installed_ = false;
 
 
 void OS::SetUp() {
@@ -1257,11 +1262,13 @@ void OS::SetUp() {
   }
 #endif
   SignalSender::SetUp();
+  CpuProfilerSignalHandler::InstallSignalHandler();
 }
 
 
 void OS::TearDown() {
   SignalSender::TearDown();
+  CpuProfilerSignalHandler::RestoreSignalHandler();
   delete limit_mutex;
 }
 
@@ -1296,4 +1303,40 @@ void Sampler::Stop() {
 }
 
 
+class CpuProfilerThread::PlatformData : public Malloced {
+ public:
+  PlatformData() : vm_tgid_(getpid()) {}
+
+  int vm_tgid() const { return vm_tgid_; }
+
+ private:
+  const int vm_tgid_;
+};
+
+
+CpuProfilerThread::CpuProfilerThread(Sampler* sampler)
+    : Thread(Thread::Options("CpuProfiler", kCpuProfilerThreadStackSize)),
+      sampler_(sampler) {
+  data_ = new PlatformData;
+}
+
+
+CpuProfilerThread::~CpuProfilerThread() {
+  delete data_;
+}
+
+
+void CpuProfilerThread::DoSample() {
+  int tid = sampler_->platform_data()->vm_tid();
+  int tgid = data_->vm_tgid();
+  if (!CpuProfilerSignalHandler::signal_handler_installed()) return;
+  // Glibc doesn't provide a wrapper for tgkill(2).
+#if defined(ANDROID)
+  syscall(__NR_tgkill, tgid, tid, SIGPROF);
+#else
+  syscall(SYS_tgkill, tgid, tid, SIGPROF);

[caseq, 2012/08/17 12:56:35]

looks like we could either use a tkill() or tgkill() with tgid of -1 instead.

+#endif
+}
+
+
 } }  // namespace v8::internal