Moving cpu profiling into its own thread.

src/platform-linux.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1037 matching lines @@
 #elif V8_HOST_ARCH_MIPS
   sample->pc = reinterpret_cast<Address>(mcontext.pc);
   sample->sp = reinterpret_cast<Address>(mcontext.gregs[29]);
   sample->fp = reinterpret_cast<Address>(mcontext.gregs[30]);
 #endif  // V8_HOST_ARCH_*
   sampler->SampleStack(sample);
   sampler->Tick(sample);
 }
 
 
+class CpuProfilerSignalHandler {
+ public:
+  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 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()) {}
+  PlatformData()
+      : vm_tgid_(getpid()),
+        vm_tid_(GetThreadID()) {}
 
-  int vm_tid() const { return vm_tid_; }
+  void SendProfilingSignal() {
+    if (!CpuProfilerSignalHandler::signal_handler_installed()) return;
+    // Glibc doesn't provide a wrapper for tgkill(2).
+#if defined(ANDROID)
+    syscall(__NR_tgkill, vm_tgid_, vm_tid_, SIGPROF);
+#else
+    syscall(SYS_tgkill, vm_tgid_, vm_tid_, SIGPROF);
+#endif
+  }
 
  private:
+  const int vm_tgid_;
   const int vm_tid_;
 };
 
 
 class SignalSender : public Thread {
  public:
   enum SleepInterval {
     HALF_INTERVAL,
     FULL_INTERVAL
   };
 
   static const int kSignalSenderStackSize = 64 * KB;
 
   explicit SignalSender(int interval)
       : Thread(Thread::Options("SignalSender", kSignalSenderStackSize)),
-        vm_tgid_(getpid()),
         interval_(interval) {}
 
   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);
     if (instance_ == NULL) {
       // Start a thread that will send SIGPROF signal to VM threads,
       // when CPU profiling will be enabled.
       instance_ = new SignalSender(sampler->interval());
       instance_->Start();
     } else {
       ASSERT(instance_->interval_ == sampler->interval());
     }
   }
 
   static void RemoveActiveSampler(Sampler* sampler) {
     ScopedLock lock(mutex_);
     SamplerRegistry::RemoveActiveSampler(sampler);
     if (SamplerRegistry::GetState() == SamplerRegistry::HAS_NO_SAMPLERS) {
       RuntimeProfiler::StopRuntimeProfilerThreadBeforeShutdown(instance_);
       delete instance_;
       instance_ = NULL;
-      RestoreSignalHandler();
     }
   }
 
   // Implement Thread::Run().
   virtual void Run() {
     SamplerRegistry::State state;
     while ((state = SamplerRegistry::GetState()) !=
            SamplerRegistry::HAS_NO_SAMPLERS) {
-      bool cpu_profiling_enabled =
-          (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) {
-        if (rate_limiter_.SuspendIfNecessary()) continue;
-      }
-      if (cpu_profiling_enabled && runtime_profiler_enabled) {
-        if (!SamplerRegistry::IterateActiveSamplers(&DoCpuProfile, this)) {
+      if (rate_limiter_.SuspendIfNecessary()) continue;
+      if (runtime_profiler_enabled) {
+        if (!SamplerRegistry::IterateActiveSamplers(&DoRuntimeProfile,
+                                                    NULL)) {
           return;
         }
-        Sleep(HALF_INTERVAL);
-        if (!SamplerRegistry::IterateActiveSamplers(&DoRuntimeProfile, NULL)) {
-          return;
-        }
-        Sleep(HALF_INTERVAL);
-      } else {
-        if (cpu_profiling_enabled) {
-          if (!SamplerRegistry::IterateActiveSamplers(&DoCpuProfile,
-                                                      this)) {
-            return;
-          }
-        }
-        if (runtime_profiler_enabled) {
-          if (!SamplerRegistry::IterateActiveSamplers(&DoRuntimeProfile,
-                                                      NULL)) {
-            return;
-          }
-        }
-        Sleep(FULL_INTERVAL);
       }
+      Sleep(FULL_INTERVAL);
     }
   }
 
-  static void DoCpuProfile(Sampler* sampler, void* raw_sender) {
-    if (!sampler->IsProfiling()) return;
-    SignalSender* sender = reinterpret_cast<SignalSender*>(raw_sender);
-    sender->SendProfilingSignal(sampler->platform_data()->vm_tid());
-  }
-
   static void DoRuntimeProfile(Sampler* sampler, void* ignored) {
     if (!sampler->isolate()->IsInitialized()) return;
     sampler->isolate()->runtime_profiler()->NotifyTick();
   }
 
-  void SendProfilingSignal(int tid) {
-    if (!signal_handler_installed_) return;
-    // Glibc doesn't provide a wrapper for tgkill(2).
-#if defined(ANDROID)
-    syscall(__NR_tgkill, vm_tgid_, tid, SIGPROF);
-#else
-    syscall(SYS_tgkill, vm_tgid_, tid, SIGPROF);
-#endif
-  }
-
   void Sleep(SleepInterval full_or_half) {
     // Convert ms to us and subtract 100 us to compensate delays
     // occuring during signal delivery.
     useconds_t interval = interval_ * 1000 - 100;
     if (full_or_half == HALF_INTERVAL) interval /= 2;
 #if defined(ANDROID)
     usleep(interval);
 #else
     int result = usleep(interval);
 #ifdef DEBUG
     if (result != 0 && errno != EINTR) {
       fprintf(stderr,
               "SignalSender usleep error; interval = %u, errno = %d\n",
               interval,
               errno);
       ASSERT(result == 0 || errno == EINTR);
     }
 #endif  // DEBUG
     USE(result);
 #endif  // ANDROID
   }
 
-  const int vm_tgid_;
   const int interval_;
   RuntimeProfilerRateLimiter rate_limiter_;
 
   // 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);
 };
 
 
 Mutex* SignalSender::mutex_ = NULL;
 SignalSender* SignalSender::instance_ = NULL;
-struct sigaction SignalSender::old_signal_handler_;
-bool SignalSender::signal_handler_installed_ = false;
 
 
 void OS::SetUp() {
   // Seed the random number generator. We preserve microsecond resolution.
   uint64_t seed = Ticks() ^ (getpid() << 16);
   srandom(static_cast<unsigned int>(seed));
   limit_mutex = CreateMutex();
 
 #ifdef __arm__
   // When running on ARM hardware check that the EABI used by V8 and
   // by the C code is the same.
   bool hard_float = OS::ArmUsingHardFloat();
   if (hard_float) {
 #if !USE_EABI_HARDFLOAT
     PrintF("ERROR: Binary compiled with -mfloat-abi=hard but without "
            "-DUSE_EABI_HARDFLOAT\n");
     exit(1);
 #endif
   } else {
 #if USE_EABI_HARDFLOAT
     PrintF("ERROR: Binary not compiled with -mfloat-abi=hard but with "
            "-DUSE_EABI_HARDFLOAT\n");
     exit(1);
 #endif
   }
 #endif
   SignalSender::SetUp();
+  CpuProfilerSignalHandler::InstallSignalHandler();

[caseq, 2012/09/03 11:59:58]

Can we do this as necessary -- e.g. when a first profiler is being started?

 }
 
 
 void OS::TearDown() {
   SignalSender::TearDown();
+  CpuProfilerSignalHandler::RestoreSignalHandler();

[caseq, 2012/09/03 11:59:58]

ditto

   delete limit_mutex;
 }
 
 
 Sampler::Sampler(Isolate* isolate, int interval)
     : isolate_(isolate),
       interval_(interval),
       profiling_(false),
       active_(false),
       samples_taken_(0) {
   data_ = new PlatformData;
 }
 
 
 Sampler::~Sampler() {
   ASSERT(!IsActive());
   delete data_;
 }
 
 
+void Sampler::DoSample() {
+  platform_data()->SendProfilingSignal();
+}
+
+
 void Sampler::Start() {
   ASSERT(!IsActive());
   SetActive(true);
   SignalSender::AddActiveSampler(this);
 }
 
 
 void Sampler::Stop() {
   ASSERT(IsActive());
   SignalSender::RemoveActiveSampler(this);
   SetActive(false);
 }
 
 
 } }  // namespace v8::internal