src/signal_catcher.cc

/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "signal_catcher.h"

#include <fcntl.h>
#include <pthread.h>
#include <signal.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>

#include "class_linker.h"
#include "file.h"
#include "heap.h"
#include "os.h"
#include "runtime.h"
#include "scoped_thread_state_change.h"
#include "signal_set.h"
#include "thread.h"
#include "thread_list.h"
#include "utils.h"

namespace art {

static void DumpCmdLine(std::ostream& os) {
#if defined(__linux__)
  // Show the original command line, and the current command line too if it's changed.
  // On Android, /proc/self/cmdline will have been rewritten to something like "system_server".
  std::string current_cmd_line;
  if (ReadFileToString("/proc/self/cmdline", &current_cmd_line)) {
    current_cmd_line.resize(current_cmd_line.size() - 1); // Lose the trailing '\0'.
    std::replace(current_cmd_line.begin(), current_cmd_line.end(), '\0', ' ');

    os << "Cmdline: " << current_cmd_line;
    const char* stashed_cmd_line = GetCmdLine();
    if (stashed_cmd_line != NULL && current_cmd_line != stashed_cmd_line) {
      os << "Original command line: " << stashed_cmd_line;
    }
  }
  os << "\n";
#else
  os << "Cmdline: " << GetCmdLine() << "\n";
#endif
}

SignalCatcher::SignalCatcher(const std::string& stack_trace_file)
    : stack_trace_file_(stack_trace_file),
      lock_("SignalCatcher lock"),
      cond_("SignalCatcher::cond_"),
      thread_(NULL) {
  SetHaltFlag(false);

  // Create a raw pthread; its start routine will attach to the runtime.
  CHECK_PTHREAD_CALL(pthread_create, (&pthread_, NULL, &Run, this), "signal catcher thread");

  Thread* self = Thread::Current();
  MutexLock mu(self, lock_);
  while (thread_ == NULL) {
    cond_.Wait(self, lock_);
  }
}

SignalCatcher::~SignalCatcher() {
  // Since we know the thread is just sitting around waiting for signals
  // to arrive, send it one.
  SetHaltFlag(true);
  CHECK_PTHREAD_CALL(pthread_kill, (pthread_, SIGQUIT), "signal catcher shutdown");
  CHECK_PTHREAD_CALL(pthread_join, (pthread_, NULL), "signal catcher shutdown");
}

void SignalCatcher::SetHaltFlag(bool new_value) {
  MutexLock mu(Thread::Current(), lock_);
  halt_ = new_value;
}

bool SignalCatcher::ShouldHalt() {
  MutexLock mu(Thread::Current(), lock_);
  return halt_;
}

void SignalCatcher::Output(const std::string& s) {
  if (stack_trace_file_.empty()) {
    LOG(INFO) << s;
    return;
  }

  ScopedThreadStateChange tsc(Thread::Current(), kWaitingForSignalCatcherOutput);
  int fd = open(stack_trace_file_.c_str(), O_APPEND | O_CREAT | O_WRONLY, 0666);
  if (fd == -1) {
    PLOG(ERROR) << "Unable to open stack trace file '" << stack_trace_file_ << "'";
    return;
  }
  UniquePtr<File> file(OS::FileFromFd(stack_trace_file_.c_str(), fd));
  if (!file->WriteFully(s.data(), s.size())) {
    PLOG(ERROR) << "Failed to write stack traces to '" << stack_trace_file_ << "'";
  } else {
    LOG(INFO) << "Wrote stack traces to '" << stack_trace_file_ << "'";
  }
  close(fd);
}

void SignalCatcher::HandleSigQuit() {
  Runtime* runtime = Runtime::Current();
  ThreadList* thread_list = runtime->GetThreadList();

  // Grab exclusively the mutator lock, set state to Runnable without checking for a pending
  // suspend request as we're going to suspend soon anyway. We set the state to Runnable to avoid
  // giving away the mutator lock.
  thread_list->SuspendAll();
  Thread* self = Thread::Current();
  Locks::mutator_lock_->AssertExclusiveHeld(self);
  const char* old_cause = self->StartAssertNoThreadSuspension("Handling sigquit");
  ThreadState old_state = self->SetStateUnsafe(kRunnable);

  std::ostringstream os;
  os << "\n"
      << "----- pid " << getpid() << " at " << GetIsoDate() << " -----\n";

  DumpCmdLine(os);

  os << "Build type: " << (kIsDebugBuild ? "debug" : "optimized") << "\n";

  runtime->DumpForSigQuit(os);

  if (false) {
    std::string maps;
    if (ReadFileToString("/proc/self/maps", &maps)) {
      os << "/proc/self/maps:\n" << maps;
    }
  }
  os << "----- end " << getpid() << " -----\n";

  CHECK_EQ(self->SetStateUnsafe(old_state), kRunnable);
  self->EndAssertNoThreadSuspension(old_cause);
  thread_list->ResumeAll();

  Output(os.str());
}

void SignalCatcher::HandleSigUsr1() {
  LOG(INFO) << "SIGUSR1 forcing GC (no HPROF)";
  Runtime::Current()->GetHeap()->CollectGarbage(false);
}

int SignalCatcher::WaitForSignal(Thread* self, SignalSet& signals) {
  ScopedThreadStateChange tsc(self, kWaitingInMainSignalCatcherLoop);

  // Signals for sigwait() must be blocked but not ignored.  We
  // block signals like SIGQUIT for all threads, so the condition
  // is met.  When the signal hits, we wake up, without any signal
  // handlers being invoked.
  int signal_number = signals.Wait();
  if (!ShouldHalt()) {
    // Let the user know we got the signal, just in case the system's too screwed for us to
    // actually do what they want us to do...
    LOG(INFO) << *self << ": reacting to signal " << signal_number;

    // If anyone's holding locks (which might prevent us from getting back into state Runnable), say so...
    Runtime::Current()->DumpLockHolders(LOG(INFO));
  }

  return signal_number;
}

void* SignalCatcher::Run(void* arg) {
  SignalCatcher* signal_catcher = reinterpret_cast<SignalCatcher*>(arg);
  CHECK(signal_catcher != NULL);

  Runtime* runtime = Runtime::Current();
  CHECK(runtime->AttachCurrentThread("Signal Catcher", true, runtime->GetSystemThreadGroup()));

  Thread* self = Thread::Current();

  {
    MutexLock mu(self, signal_catcher->lock_);
    signal_catcher->thread_ = self;
    signal_catcher->cond_.Broadcast();
  }

  // Set up mask with signals we want to handle.
  SignalSet signals;
  signals.Add(SIGQUIT);
  signals.Add(SIGUSR1);

  while (true) {
    int signal_number = signal_catcher->WaitForSignal(self, signals);
    if (signal_catcher->ShouldHalt()) {
      runtime->DetachCurrentThread();
      return NULL;
    }

    switch (signal_number) {
    case SIGQUIT:
      signal_catcher->HandleSigQuit();
      break;
    case SIGUSR1:
      signal_catcher->HandleSigUsr1();
      break;
    default:
      LOG(ERROR) << "Unexpected signal %d" << signal_number;
      break;
    }
  }
}

}  // namespace art