Try to simplify the semantics of the profiling code by making...

src/platform-linux.cc

 // Copyright 2006-2008 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 730 matching lines @@
   }
   return false;
 }
 
 
 static void ProfilerSignalHandler(int signal, siginfo_t* info, void* context) {
 #ifndef V8_HOST_ARCH_MIPS
   USE(info);
   if (signal != SIGPROF) return;
   if (active_sampler_ == NULL) return;
+  if (!IsVmThread()) return;
 
   TickSample sample_obj;
   TickSample* sample = CpuProfiler::TickSampleEvent();
   if (sample == NULL) sample = &sample_obj;
 
   // We always sample the VM state.
   sample->state = VMState::current_state();
+
   // If profiling, we extract the current pc and sp.
   if (active_sampler_->IsProfiling()) {
     // Extracting the sample from the context is extremely machine dependent.
     ucontext_t* ucontext = reinterpret_cast<ucontext_t*>(context);
     mcontext_t& mcontext = ucontext->uc_mcontext;
 #if V8_HOST_ARCH_IA32
     sample->pc = reinterpret_cast<Address>(mcontext.gregs[REG_EIP]);
     sample->sp = reinterpret_cast<Address>(mcontext.gregs[REG_ESP]);
     sample->fp = reinterpret_cast<Address>(mcontext.gregs[REG_EBP]);
 #elif V8_HOST_ARCH_X64
     sample->pc = reinterpret_cast<Address>(mcontext.gregs[REG_RIP]);
     sample->sp = reinterpret_cast<Address>(mcontext.gregs[REG_RSP]);
     sample->fp = reinterpret_cast<Address>(mcontext.gregs[REG_RBP]);
 #elif V8_HOST_ARCH_ARM
 // An undefined macro evaluates to 0, so this applies to Android's Bionic also.
 #if (__GLIBC__ < 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ <= 3))
     sample->pc = reinterpret_cast<Address>(mcontext.gregs[R15]);
     sample->sp = reinterpret_cast<Address>(mcontext.gregs[R13]);
     sample->fp = reinterpret_cast<Address>(mcontext.gregs[R11]);
 #else
     sample->pc = reinterpret_cast<Address>(mcontext.arm_pc);
     sample->sp = reinterpret_cast<Address>(mcontext.arm_sp);
     sample->fp = reinterpret_cast<Address>(mcontext.arm_fp);
 #endif
 #elif V8_HOST_ARCH_MIPS
     // Implement this on MIPS.
     UNIMPLEMENTED();
 #endif
-    if (IsVmThread()) {
-      active_sampler_->SampleStack(sample);
-    }
+    active_sampler_->SampleStack(sample);
   }
 
   active_sampler_->Tick(sample);
 #endif
 }
 
 
 class Sampler::PlatformData : public Malloced {
  public:
   PlatformData() {
     signal_handler_installed_ = false;
   }
 
   bool signal_handler_installed_;
   struct sigaction old_signal_handler_;
   struct itimerval old_timer_value_;
 };
 
 
 Sampler::Sampler(int interval, bool profiling)
-    : interval_(interval), profiling_(profiling), active_(false) {
+    : interval_(interval),
+      profiling_(profiling),
+      synchronous_(profiling),
+      active_(false) {
   data_ = new PlatformData();
 }
 
 
 Sampler::~Sampler() {
   delete data_;
 }
 
 
 void Sampler::Start() {
@@ skipping 35 matching lines @@
 
   // This sampler is no longer the active sampler.
   active_sampler_ = NULL;
   active_ = false;
 }
 
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal