src/optimizing-compiler-thread.cc

// Copyright 2012 the V8 project authors. All rights reserved.
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#include "optimizing-compiler-thread.h"

#include "v8.h"

#include "full-codegen.h"
#include "hydrogen.h"
#include "isolate.h"
#include "v8threads.h"

namespace v8 {
namespace internal {


void OptimizingCompilerThread::Run() {
#ifdef DEBUG
  { LockGuard<Mutex> lock_guard(&thread_id_mutex_);
    thread_id_ = ThreadId::Current().ToInteger();
  }
#endif
  Isolate::SetIsolateThreadLocals(isolate_, NULL);
  DisallowHeapAllocation no_allocation;
  DisallowHandleAllocation no_handles;
  DisallowHandleDereference no_deref;

  ElapsedTimer total_timer;
  if (FLAG_trace_concurrent_recompilation) total_timer.Start();

  while (true) {
    input_queue_semaphore_.Wait();
    Logger::TimerEventScope timer(
        isolate_, Logger::TimerEventScope::v8_recompile_concurrent);

    if (FLAG_concurrent_recompilation_delay != 0) {
      OS::Sleep(FLAG_concurrent_recompilation_delay);
    }

    switch (static_cast<StopFlag>(Acquire_Load(&stop_thread_))) {
      case CONTINUE:
        break;
      case STOP:
        if (FLAG_trace_concurrent_recompilation) {
          time_spent_total_ = total_timer.Elapsed();
        }
        stop_semaphore_.Signal();
        return;
      case FLUSH:
        // The main thread is blocked, waiting for the stop semaphore.
        { AllowHandleDereference allow_handle_dereference;
          FlushInputQueue(true);
        }
        Release_Store(&stop_thread_, static_cast<AtomicWord>(CONTINUE));
        stop_semaphore_.Signal();
        // Return to start of consumer loop.
        continue;
    }

    ElapsedTimer compiling_timer;
    if (FLAG_trace_concurrent_recompilation) compiling_timer.Start();

    CompileNext();

    if (FLAG_trace_concurrent_recompilation) {
      time_spent_compiling_ += compiling_timer.Elapsed();
    }
  }
}


void OptimizingCompilerThread::CompileNext() {
  RecompileJob* job = NULL;
  bool result = input_queue_.Dequeue(&job);
  USE(result);
  ASSERT(result);
  Barrier_AtomicIncrement(&queue_length_, static_cast<Atomic32>(-1));

  // The function may have already been optimized by OSR.  Simply continue.
  RecompileJob::Status status = job->OptimizeGraph();
  USE(status);   // Prevent an unused-variable error in release mode.
  ASSERT(status != RecompileJob::FAILED);

  // The function may have already been optimized by OSR.  Simply continue.
  // Use a mutex to make sure that functions marked for install
  // are always also queued.
  output_queue_.Enqueue(job);
  isolate_->stack_guard()->RequestInstallCode();
}


static void DisposeRecompileJob(RecompileJob* job,
                                bool restore_function_code) {
  // The recompile job is allocated in the CompilationInfo's zone.
  CompilationInfo* info = job->info();
  if (restore_function_code) {
    if (info->is_osr()) {
      if (!job->IsWaitingForInstall()) BackEdgeTable::RemoveStackCheck(info);
    } else {
      Handle<JSFunction> function = info->closure();
      function->ReplaceCode(function->shared()->code());
    }
  }
  delete info;
}


void OptimizingCompilerThread::FlushInputQueue(bool restore_function_code) {
  RecompileJob* job;
  while (input_queue_.Dequeue(&job)) {
    // This should not block, since we have one signal on the input queue
    // semaphore corresponding to each element in the input queue.
    input_queue_semaphore_.Wait();
    // OSR jobs are dealt with separately.
    if (!job->info()->is_osr()) {
      DisposeRecompileJob(job, restore_function_code);
    }
  }
  Release_Store(&queue_length_, static_cast<AtomicWord>(0));
}


void OptimizingCompilerThread::FlushOutputQueue(bool restore_function_code) {
  RecompileJob* job;
  while (output_queue_.Dequeue(&job)) {
    // OSR jobs are dealt with separately.
    if (!job->info()->is_osr()) {
      DisposeRecompileJob(job, restore_function_code);
    }
  }
}


void OptimizingCompilerThread::FlushOsrBuffer(bool restore_function_code) {
  RecompileJob* job;
  for (int i = 0; i < osr_buffer_size_; i++) {
    job = osr_buffer_[i];
    if (job != NULL) DisposeRecompileJob(job, restore_function_code);
  }
  osr_cursor_ = 0;
}


void OptimizingCompilerThread::Flush() {
  ASSERT(!IsOptimizerThread());
  Release_Store(&stop_thread_, static_cast<AtomicWord>(FLUSH));
  input_queue_semaphore_.Signal();
  stop_semaphore_.Wait();
  FlushOutputQueue(true);
  if (FLAG_concurrent_osr) FlushOsrBuffer(true);
  if (FLAG_trace_concurrent_recompilation) {
    PrintF("  ** Flushed concurrent recompilation queues.\n");
  }
}


void OptimizingCompilerThread::Stop() {
  ASSERT(!IsOptimizerThread());
  Release_Store(&stop_thread_, static_cast<AtomicWord>(STOP));
  input_queue_semaphore_.Signal();
  stop_semaphore_.Wait();

  if (FLAG_concurrent_recompilation_delay != 0) {
    // Barrier when loading queue length is not necessary since the write
    // happens in CompileNext on the same thread.
    // This is used only for testing.
    while (NoBarrier_Load(&queue_length_) > 0) CompileNext();
    InstallOptimizedFunctions();
  } else {
    FlushInputQueue(false);
    FlushOutputQueue(false);
  }

  if (FLAG_concurrent_osr) FlushOsrBuffer(false);

  if (FLAG_trace_concurrent_recompilation) {
    double percentage = time_spent_compiling_.PercentOf(time_spent_total_);
    PrintF("  ** Compiler thread did %.2f%% useful work\n", percentage);
  }

  if ((FLAG_trace_osr || FLAG_trace_concurrent_recompilation) &&
      FLAG_concurrent_osr) {
    PrintF("[COSR hit rate %d / %d]\n", osr_hits_, osr_attempts_);
  }

  Join();
}


void OptimizingCompilerThread::InstallOptimizedFunctions() {
  ASSERT(!IsOptimizerThread());
  HandleScope handle_scope(isolate_);

  RecompileJob* job;
  while (output_queue_.Dequeue(&job)) {
    CompilationInfo* info = job->info();
    if (info->is_osr()) {
      if (FLAG_trace_osr) {
        PrintF("[COSR - ");
        info->closure()->PrintName();
        PrintF(" is ready for install and entry at AST id %d]\n",
               info->osr_ast_id().ToInt());
      }
      job->WaitForInstall();
      BackEdgeTable::RemoveStackCheck(info);
    } else {
      Compiler::InstallOptimizedCode(job);
    }
  }
}


void OptimizingCompilerThread::QueueForOptimization(RecompileJob* job) {
  ASSERT(IsQueueAvailable());
  ASSERT(!IsOptimizerThread());
  Barrier_AtomicIncrement(&queue_length_, static_cast<Atomic32>(1));
  CompilationInfo* info = job->info();
  if (info->is_osr()) {
    if (FLAG_trace_concurrent_recompilation) {
      PrintF("  ** Queueing ");
      info->closure()->PrintName();
      PrintF(" for concurrent on-stack replacement.\n");
    }
    AddToOsrBuffer(job);
    osr_attempts_++;
    BackEdgeTable::AddStackCheck(info);
  } else {
    info->closure()->MarkInRecompileQueue();
  }
  input_queue_.Enqueue(job);
  input_queue_semaphore_.Signal();
}


RecompileJob* OptimizingCompilerThread::FindReadyOSRCandidate(
    Handle<JSFunction> function, uint32_t osr_pc_offset) {
  ASSERT(!IsOptimizerThread());
  RecompileJob* result = NULL;
  for (int i = 0; i < osr_buffer_size_; i++) {
    result = osr_buffer_[i];
    if (result == NULL) continue;
    if (result->IsWaitingForInstall() &&
        result->info()->HasSameOsrEntry(function, osr_pc_offset)) {
      osr_hits_++;
      osr_buffer_[i] = NULL;
      return result;
    }
  }
  return NULL;
}


bool OptimizingCompilerThread::IsQueuedForOSR(Handle<JSFunction> function,
                                              uint32_t osr_pc_offset) {
  ASSERT(!IsOptimizerThread());
  for (int i = 0; i < osr_buffer_size_; i++) {
    if (osr_buffer_[i] != NULL &&
        osr_buffer_[i]->info()->HasSameOsrEntry(function, osr_pc_offset)) {
      return !osr_buffer_[i]->IsWaitingForInstall();
    }
  }
  return false;
}


bool OptimizingCompilerThread::IsQueuedForOSR(JSFunction* function) {
  ASSERT(!IsOptimizerThread());
  for (int i = 0; i < osr_buffer_size_; i++) {
    if (osr_buffer_[i] != NULL &&
        *osr_buffer_[i]->info()->closure() == function) {
      return !osr_buffer_[i]->IsWaitingForInstall();
    }
  }
  return false;
}


void OptimizingCompilerThread::AddToOsrBuffer(RecompileJob* job) {
  ASSERT(!IsOptimizerThread());
  // Store into next empty slot or replace next stale OSR job that's waiting
  // in vain.  Dispose in the latter case.
  RecompileJob* stale;
  while (true) {
    stale = osr_buffer_[osr_cursor_];
    if (stale == NULL) break;
    if (stale->IsWaitingForInstall()) {
      CompilationInfo* info = stale->info();
      if (FLAG_trace_osr) {
        PrintF("[COSR - Discarded ");
        info->closure()->PrintName();
        PrintF(", AST id %d]\n", info->osr_ast_id().ToInt());
      }
      DisposeRecompileJob(stale, false);
      break;
    }
    AdvanceOsrCursor();
  }

  osr_buffer_[osr_cursor_] = job;
  AdvanceOsrCursor();
}


#ifdef DEBUG
bool OptimizingCompilerThread::IsOptimizerThread() {
  if (!FLAG_concurrent_recompilation) return false;
  LockGuard<Mutex> lock_guard(&thread_id_mutex_);
  return ThreadId::Current().ToInteger() == thread_id_;
}
#endif


} }  // namespace v8::internal