[Linux] Do not install SIGPROF handler until we

start CPU profiling.

TBR=vitalyr@chromium.org
BUG=1344,crbug/79320,crbug/83521
TEST=none

Review URL: http://codereview.chromium.org/7107003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8152 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/platform-linux.cc

@@ -979,19 +979,28 @@ class SignalSender : public Thread {
         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 {
@@ -1007,12 +1016,7 @@ class SignalSender : public Thread {
       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();
     }
   }
 
@@ -1024,6 +1028,10 @@ class SignalSender : public Thread {
       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) {