[Linux] Do not install SIGPROF handler until we

src/platform-linux.cc

 // Copyright 2011 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 961 matching lines @@
   enum SleepInterval {
     HALF_INTERVAL,
     FULL_INTERVAL
   };
 
   explicit SignalSender(int interval)
       : Thread(NULL, "SignalSender"),
         vm_tgid_(getpid()),
         interval_(interval) {}
 
+  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) {
-      // Install a signal handler.
-      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);
-
-      // Start a thread that sends SIGPROF signal to VM threads.
+      // 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::WakeUpRuntimeProfilerThreadBeforeShutdown();
       instance_->Join();
       delete instance_;
       instance_ = NULL;
-
-      // Restore the old signal handler.
-      if (signal_handler_installed_) {
-        sigaction(SIGPROF, &old_signal_handler_, 0);
-        signal_handler_installed_ = false;
-      }
+      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_)

[Mads Ager (chromium), 2011/06/02 10:26:55]

Drive-by: please use braces around the bodies of if statements. We can just fix
this on bleeding_edge and leave it as is on the branches.

+        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)) {
           return;
         }
         Sleep(HALF_INTERVAL);
@@ skipping 103 matching lines @@
 
 void Sampler::Stop() {
   ASSERT(IsActive());
   SignalSender::RemoveActiveSampler(this);
   SetActive(false);
 }
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal