Get rid of UnsafeCurrent in Sampler

src/profiler/sampler.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/profiler/sampler.h"
 
 #if V8_OS_POSIX && !V8_OS_CYGWIN
 
 #define USE_SIGNALS
 
@@ skipping 24 matching lines @@
     !defined(__BIONIC_HAVE_STRUCT_SIGCONTEXT)
 #include <asm/sigcontext.h>  // NOLINT
 #endif
 
 #elif V8_OS_WIN || V8_OS_CYGWIN
 
 #include "src/base/win32-headers.h"
 
 #endif
 
+#include "src/atomic-utils.h"
 #include "src/base/platform/platform.h"
 #include "src/flags.h"
 #include "src/frames-inl.h"
 #include "src/log.h"
 #include "src/profiler/cpu-profiler-inl.h"
 #include "src/simulator.h"
 #include "src/v8threads.h"
 #include "src/vm-state-inl.h"
 
 
@@ skipping 174 matching lines @@
         // pessimistically assume it could be the entire pattern match.
         MSAN_MEMORY_IS_INITIALIZED(pc, pattern->bytes_count - offset);
         if (!memcmp(pc, pattern->bytes + offset, pattern->bytes_count - offset))
           return true;
       }
     }
   }
   return false;
 }
 
+typedef List<Sampler*> SamplerList;
+
+#if defined(USE_SIGNALS)
+class AtomicGuard {
+ public:
+  explicit AtomicGuard(AtomicValue<int>* atomic, bool is_block = true)
+      : atomic_(atomic),
+        is_success_(false) {
+    do {
+      // Use Acquire_Load to gain mutual exclusion, so that
+      // TSAN recognizes the atomic variable acting as guard.

[jochen (gone - plz use gerrit), 2016/04/21 14:44:24]

i think the point is that it doesn't act as a guard unless you do this.

[alph, 2016/04/21 16:21:28]

Why? To me it looks more like TSAN bug. Isn't TrySetValue imply use because it
has to read the value to make the comparison.

[Michael Lippautz, 2016/04/21 16:34:18]

dbc (basically the comment from the other CL): 
TrySetValue currently *only* implies a Release barrier (not acquire). This is
far from ideal. To support stand-alone use cases (like the one above without the
load) and load/cas scenarios (like it's modeled now) we should have a full
barrier in the CAS.

+      USE(atomic_->Value());
+      is_success_ = atomic_->TrySetValue(0, 1);
+    } while (is_block && !is_success_);
+  }
+
+  bool is_success() { return is_success_; }
+
+  ~AtomicGuard() {
+    if (is_success_) {
+      atomic_->SetValue(0);
+    }
+    atomic_ = NULL;
+  }
+
+ private:
+  AtomicValue<int>* atomic_;
+  bool is_success_;
+};
+
+
+// Returns key for hash map.
+void* ThreadKey(pthread_t thread_id) {
+  return reinterpret_cast<void*>(thread_id);
+}
+
+
+// Returns hash value for hash map.
+uint32_t ThreadHash(pthread_t thread_id) {
+#if V8_OS_MACOSX
+  return static_cast<uint32_t>(reinterpret_cast<intptr_t>(thread_id));
+#else
+  return static_cast<uint32_t>(thread_id);
+#endif
+}
+#endif  // USE_SIGNALS
+
 }  // namespace
 
 #if defined(USE_SIGNALS)
 
 class Sampler::PlatformData : public PlatformDataCommon {
  public:
   PlatformData() : vm_tid_(pthread_self()) {}
   pthread_t vm_tid() const { return vm_tid_; }
 
  private:
@@ skipping 118 matching lines @@
 
   static void DecreaseSamplerCount() {
     base::LockGuard<base::Mutex> lock_guard(mutex_);
     if (--client_count_ == 0) Restore();
   }
 
   static bool Installed() {
     return signal_handler_installed_;
   }
 
+#if !V8_OS_NACL
+  static void CollectSample(void* context, Sampler* sampler);
+#endif
+
  private:
   static void Install() {
 #if !V8_OS_NACL
     struct sigaction sa;
     sa.sa_sigaction = &HandleProfilerSignal;
     sigemptyset(&sa.sa_mask);
 #if V8_OS_QNX
     sa.sa_flags = SA_SIGINFO;
 #else
     sa.sa_flags = SA_RESTART | SA_SIGINFO;
@@ skipping 24 matching lines @@
 
 
 base::Mutex* SignalHandler::mutex_ = NULL;
 int SignalHandler::client_count_ = 0;
 struct sigaction SignalHandler::old_signal_handler_;
 bool SignalHandler::signal_handler_installed_ = false;
 
 
 // As Native Client does not support signal handling, profiling is disabled.
 #if !V8_OS_NACL
-void SignalHandler::HandleProfilerSignal(int signal, siginfo_t* info,
-                                         void* context) {
-  USE(info);
-  if (signal != SIGPROF) return;
-  Isolate* isolate = Isolate::UnsafeCurrent();
-  if (isolate == NULL || !isolate->IsInUse()) {
-    // We require a fully initialized and entered isolate.
+void SignalHandler::CollectSample(void* context, Sampler* sampler) {
+  if (sampler == NULL || (!sampler->IsProfiling() &&
+                          !sampler->IsRegistered())) {
     return;
   }
+  Isolate* isolate = sampler->isolate();
+
+  // We require a fully initialized and entered isolate.
+  if (isolate == NULL || !isolate->IsInUse()) return;
+
   if (v8::Locker::IsActive() &&
       !isolate->thread_manager()->IsLockedByCurrentThread()) {
     return;
   }
 
-  Sampler* sampler = isolate->logger()->sampler();
-  if (sampler == NULL) return;
-
   v8::RegisterState state;
 
 #if defined(USE_SIMULATOR)
   SimulatorHelper helper;
   if (!helper.Init(isolate)) return;
   helper.FillRegisters(&state);
   // It possible that the simulator is interrupted while it is updating
   // the sp or fp register. ARM64 simulator does this in two steps:
   // first setting it to zero and then setting it to the new value.
   // Bailout if sp/fp doesn't contain the new value.
@@ skipping 127 matching lines @@
 #elif V8_OS_AIX
   state.pc = reinterpret_cast<Address>(mcontext.jmp_context.iar);
   state.sp = reinterpret_cast<Address>(mcontext.jmp_context.gpr[1]);
   state.fp = reinterpret_cast<Address>(mcontext.jmp_context.gpr[31]);
 #endif  // V8_OS_AIX
 #endif  // USE_SIMULATOR
   sampler->SampleStack(state);
 }
 #endif  // V8_OS_NACL
 
-#endif
+#endif  // USE_SIGNALS
 
 
 class SamplerThread : public base::Thread {
  public:
   static const int kSamplerThreadStackSize = 64 * KB;
 
   explicit SamplerThread(int interval)
       : Thread(base::Thread::Options("SamplerThread", kSamplerThreadStackSize)),
         interval_(interval) {}
 
   static void SetUp() { if (!mutex_) mutex_ = new base::Mutex(); }
   static void TearDown() { delete mutex_; mutex_ = NULL; }
 
   static void AddActiveSampler(Sampler* sampler) {
     bool need_to_start = false;
     base::LockGuard<base::Mutex> lock_guard(mutex_);
     if (instance_ == NULL) {
       // Start a thread that will send SIGPROF signal to VM threads,
       // when CPU profiling will be enabled.
       instance_ = new SamplerThread(sampler->interval());
       need_to_start = true;
     }
 
     DCHECK(sampler->IsActive());
+    DCHECK(instance_->interval_ == sampler->interval());
+
+#if defined(USE_SIGNALS)
+    AddSampler(sampler);
+#else
     DCHECK(!instance_->active_samplers_.Contains(sampler));
-    DCHECK(instance_->interval_ == sampler->interval());
     instance_->active_samplers_.Add(sampler);
+#endif  // USE_SIGNALS
 
     if (need_to_start) instance_->StartSynchronously();
   }
 
-  static void RemoveActiveSampler(Sampler* sampler) {
+  static void RemoveSampler(Sampler* sampler) {
     SamplerThread* instance_to_remove = NULL;
     {
       base::LockGuard<base::Mutex> lock_guard(mutex_);
 
-      DCHECK(sampler->IsActive());
+      DCHECK(sampler->IsActive() || sampler->IsRegistered());
+#if defined(USE_SIGNALS)
+      {
+        AtomicGuard atomic_guard(&sampler_list_access_counter_);
+        // Remove sampler from map.
+        pthread_t thread_id = sampler->platform_data()->vm_tid();
+        void* thread_key = ThreadKey(thread_id);
+        uint32_t thread_hash = ThreadHash(thread_id);
+        HashMap::Entry* entry =
+            thread_id_to_samplers_.Get().Lookup(thread_key, thread_hash);
+        DCHECK(entry != NULL);
+        SamplerList* samplers = reinterpret_cast<SamplerList*>(entry->value);
+        samplers->RemoveElement(sampler);
+        if (samplers->is_empty()) {
+          thread_id_to_samplers_.Pointer()->Remove(thread_key, thread_hash);
+          delete samplers;
+        }
+        if (thread_id_to_samplers_.Get().occupancy() == 0) {
+          instance_to_remove = instance_;
+          instance_ = NULL;
+        }
+      }
+#else
       bool removed = instance_->active_samplers_.RemoveElement(sampler);
       DCHECK(removed);
       USE(removed);
 
       // We cannot delete the instance immediately as we need to Join() the
       // thread but we are holding mutex_ and the thread may try to acquire it.
       if (instance_->active_samplers_.is_empty()) {
         instance_to_remove = instance_;
         instance_ = NULL;
       }
+#endif  // USE_SIGNALS
     }
 
     if (!instance_to_remove) return;
     instance_to_remove->Join();
     delete instance_to_remove;
   }
 
+  // Unlike AddActiveSampler, this method only adds a sampler,
+  // but won't start the sampler thread.
+  static void RegisterSampler(Sampler* sampler) {
+    base::LockGuard<base::Mutex> lock_guard(mutex_);
+#if defined(USE_SIGNALS)
+    AddSampler(sampler);
+#endif  // USE_SIGNALS
+  }
+
   // Implement Thread::Run().
   virtual void Run() {
     while (true) {
       {
         base::LockGuard<base::Mutex> lock_guard(mutex_);
+#if defined(USE_SIGNALS)
+        if (thread_id_to_samplers_.Get().occupancy() == 0) break;
+        if (SignalHandler::Installed()) {
+          for (HashMap::Entry *p = thread_id_to_samplers_.Get().Start();
+               p != NULL; p = thread_id_to_samplers_.Get().Next(p)) {
+            pthread_t thread_id = reinterpret_cast<pthread_t>(p->key);
+            pthread_kill(thread_id, SIGPROF);
+          }
+        }
+#else
         if (active_samplers_.is_empty()) break;
         // When CPU profiling is enabled both JavaScript and C++ code is
         // profiled. We must not suspend.
         for (int i = 0; i < active_samplers_.length(); ++i) {
           Sampler* sampler = active_samplers_.at(i);
           if (!sampler->IsProfiling()) continue;
           sampler->DoSample();
         }
+#endif  // USE_SIGNALS
       }
       base::OS::Sleep(base::TimeDelta::FromMilliseconds(interval_));
     }
   }
 
  private:
   // Protects the process wide state below.
   static base::Mutex* mutex_;
   static SamplerThread* instance_;
 
   const int interval_;
-  List<Sampler*> active_samplers_;
+
+#if defined(USE_SIGNALS)
+  struct HashMapCreateTrait {
+    static void Construct(HashMap* allocated_ptr) {
+      new (allocated_ptr) HashMap(HashMap::PointersMatch);
+    }
+  };
+  friend class SignalHandler;
+  static base::LazyInstance<HashMap, HashMapCreateTrait>::type
+      thread_id_to_samplers_;
+  static AtomicValue<int> sampler_list_access_counter_;
+  static void AddSampler(Sampler* sampler) {
+    AtomicGuard atomic_guard(&sampler_list_access_counter_);
+    // Add sampler into map if needed.
+    pthread_t thread_id = sampler->platform_data()->vm_tid();
+    HashMap::Entry *entry =
+        thread_id_to_samplers_.Pointer()->LookupOrInsert(ThreadKey(thread_id),
+                                                         ThreadHash(thread_id));
+    if (entry->value == NULL) {
+      SamplerList* samplers = new SamplerList();
+      samplers->Add(sampler);
+      entry->value = samplers;
+    } else {
+      SamplerList* samplers = reinterpret_cast<SamplerList*>(entry->value);
+      if (!samplers->Contains(sampler)) {
+        samplers->Add(sampler);
+      }
+    }
+  }
+#else
+  SamplerList active_samplers_;
+#endif  // USE_SIGNALS
 
   DISALLOW_COPY_AND_ASSIGN(SamplerThread);
 };
 
 
 base::Mutex* SamplerThread::mutex_ = NULL;
 SamplerThread* SamplerThread::instance_ = NULL;
+#if defined(USE_SIGNALS)
+base::LazyInstance<HashMap, SamplerThread::HashMapCreateTrait>::type
+    SamplerThread::thread_id_to_samplers_ = LAZY_INSTANCE_INITIALIZER;
+AtomicValue<int> SamplerThread::sampler_list_access_counter_(0);
+
+// As Native Client does not support signal handling, profiling is disabled.
+#if !V8_OS_NACL
+void SignalHandler::HandleProfilerSignal(int signal, siginfo_t* info,
+                                         void* context) {
+  USE(info);
+  if (signal != SIGPROF) return;
+  AtomicGuard atomic_guard(&SamplerThread::sampler_list_access_counter_, false);
+  if (!atomic_guard.is_success()) return;
+  pthread_t thread_id = pthread_self();
+  HashMap::Entry* entry =
+      SamplerThread::thread_id_to_samplers_.Pointer()->Lookup(
+          ThreadKey(thread_id), ThreadHash(thread_id));
+  if (entry == NULL)
+    return;
+  SamplerList* samplers = reinterpret_cast<SamplerList*>(entry->value);
+  for (int i = 0; i < samplers->length(); ++i) {
+    Sampler* sampler = samplers->at(i);
+    CollectSample(context, sampler);
+  }
+}
+#endif  // !V8_OS_NACL
+#endif  // USE_SIGNALs
 
 
 //
 // StackTracer implementation
 //
 DISABLE_ASAN void TickSample::Init(Isolate* isolate,
                                    const v8::RegisterState& regs,
                                    RecordCEntryFrame record_c_entry_frame,
                                    bool update_stats) {
   timestamp = base::TimeTicks::HighResolutionNow();
@@ skipping 100 matching lines @@
   SignalHandler::TearDown();
 #endif
 }
 
 Sampler::Sampler(Isolate* isolate, int interval)
     : isolate_(isolate),
       interval_(interval),
       profiling_(false),
       has_processing_thread_(false),
       active_(false),
+      registered_(false),
       is_counting_samples_(false),
       js_sample_count_(0),
       external_sample_count_(0) {
   data_ = new PlatformData;
 }
 
 Sampler::~Sampler() {
   DCHECK(!IsActive());
+  if (IsRegistered()) {
+    SamplerThread::RemoveSampler(this);
+  }
   delete data_;
 }
 
 void Sampler::Start() {
   DCHECK(!IsActive());
   SetActive(true);
   SamplerThread::AddActiveSampler(this);
 }
 
 
 void Sampler::Stop() {
   DCHECK(IsActive());
-  SamplerThread::RemoveActiveSampler(this);
+  SamplerThread::RemoveSampler(this);
   SetActive(false);
+  SetRegistered(false);
 }
 
 
 void Sampler::IncreaseProfilingDepth() {
   base::NoBarrier_AtomicIncrement(&profiling_, 1);
 #if defined(USE_SIGNALS)
   SignalHandler::IncreaseSamplerCount();
 #endif
 }
 
@@ skipping 19 matching lines @@
   if (sample != &sample_obj) {
     isolate_->cpu_profiler()->FinishTickSample();
   }
 }
 
 
 #if defined(USE_SIGNALS)
 
 void Sampler::DoSample() {
   if (!SignalHandler::Installed()) return;
+  if (!IsActive() && !IsRegistered()) {
+    SamplerThread::RegisterSampler(this);
+    SetRegistered(true);
+  }
   pthread_kill(platform_data()->vm_tid(), SIGPROF);
 }
 
 #elif V8_OS_WIN || V8_OS_CYGWIN
 
 void Sampler::DoSample() {
   HANDLE profiled_thread = platform_data()->profiled_thread();
   if (profiled_thread == NULL) return;
 
 #if defined(USE_SIMULATOR)
@@ skipping 26 matching lines @@
     SampleStack(state);
   }
   ResumeThread(profiled_thread);
 }
 
 #endif  // USE_SIGNALS
 
 
 }  // namespace internal
 }  // namespace v8