mash: Cleanly exit on SIGTERM, SIGINT, SIGHUP

chrome/app/shutdown_signal_handlers_posix.cc

+// Copyright 2017 The Chromium 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 "chrome/app/shutdown_signal_handlers_posix.h"
+
+#include <limits.h>
+#include <signal.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "base/callback.h"
+#include "base/debug/leak_annotations.h"
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/posix/eintr_wrapper.h"
+#include "base/single_thread_task_runner.h"
+#include "base/threading/platform_thread.h"
+#include "base/threading/thread_task_runner_handle.h"
+
+namespace {
+
+// The OSX fork() implementation can crash in the child process before

[James Cook, 2017/03/01 18:24:38]

This code is a straight cut-paste from chrome_browser_main_posix.cc. Differences
are noted below.

+// fork() returns.  In that case, the shutdown pipe will still be
+// shared with the parent process.  To prevent child crashes from
+// causing parent shutdowns, |g_pipe_pid| is the pid for the process
+// which registered |g_shutdown_pipe_write_fd|.
+// See <http://crbug.com/175341>.
+pid_t g_pipe_pid = -1;
+int g_shutdown_pipe_write_fd = -1;
+int g_shutdown_pipe_read_fd = -1;
+
+// Common code between SIG{HUP, INT, TERM}Handler.
+void GracefulShutdownHandler(int signal) {
+  // Reinstall the default handler.  We had one shot at graceful shutdown.
+  struct sigaction action;
+  memset(&action, 0, sizeof(action));
+  action.sa_handler = SIG_DFL;
+  RAW_CHECK(sigaction(signal, &action, NULL) == 0);
+
+  RAW_CHECK(g_pipe_pid != -1);
+  RAW_CHECK(g_shutdown_pipe_write_fd != -1);
+  RAW_CHECK(g_shutdown_pipe_read_fd != -1);
+  RAW_CHECK(g_pipe_pid == getpid());
+  size_t bytes_written = 0;
+  do {
+    int rv = HANDLE_EINTR(
+        write(g_shutdown_pipe_write_fd,
+              reinterpret_cast<const char*>(&signal) + bytes_written,
+              sizeof(signal) - bytes_written));
+    RAW_CHECK(rv >= 0);
+    bytes_written += rv;
+  } while (bytes_written < sizeof(signal));
+}
+
+void SIGHUPHandler(int signal) {
+  RAW_CHECK(signal == SIGHUP);
+  GracefulShutdownHandler(signal);
+}
+
+void SIGINTHandler(int signal) {
+  RAW_CHECK(signal == SIGINT);
+  GracefulShutdownHandler(signal);
+}
+
+void SIGTERMHandler(int signal) {
+  RAW_CHECK(signal == SIGTERM);
+  GracefulShutdownHandler(signal);
+}
+
+// Runs a thread that invokes a callback when a termination signal handler
+// is invoked. Uses a pipe to wait for the signal handler to run.
+class ShutdownDetector : public base::PlatformThread::Delegate {
+ public:
+  ShutdownDetector(
+      int shutdown_fd,
+      const base::Closure& shutdown_callback,
+      const scoped_refptr<base::SingleThreadTaskRunner>& task_runner);

[James Cook, 2017/03/01 18:24:38]

Added the task runner and callback.

+  ~ShutdownDetector() override;

[James Cook, 2017/03/01 18:24:38]

Added destructor.

+
+  // base::PlatformThread::Delegate:
+  void ThreadMain() override;
+
+ private:
+  const int shutdown_fd_;
+  const base::Closure shutdown_callback_;
+  const scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+  DISALLOW_COPY_AND_ASSIGN(ShutdownDetector);
+};
+
+ShutdownDetector::ShutdownDetector(
+    int shutdown_fd,
+    const base::Closure& shutdown_callback,
+    const scoped_refptr<base::SingleThreadTaskRunner>& task_runner)
+    : shutdown_fd_(shutdown_fd),
+      shutdown_callback_(shutdown_callback),
+      task_runner_(task_runner) {
+  CHECK_NE(shutdown_fd_, -1);
+  CHECK(!shutdown_callback.is_null());
+  CHECK(task_runner_);
+}
+
+ShutdownDetector::~ShutdownDetector() {}
+
+// These functions are used to help us diagnose crash dumps that happen
+// during the shutdown process.
+NOINLINE void ShutdownFDReadError() {
+  // Ensure function isn't optimized away.
+  asm("");
+  sleep(UINT_MAX);
+}
+
+NOINLINE void ShutdownFDClosedError() {
+  // Ensure function isn't optimized away.
+  asm("");
+  sleep(UINT_MAX);
+}
+
+NOINLINE void ExitPosted() {
+  // Ensure function isn't optimized away.
+  asm("");
+  sleep(UINT_MAX);
+}
+
+void ShutdownDetector::ThreadMain() {
+  base::PlatformThread::SetName("CrShutdownDetector");
+
+  int signal;
+  size_t bytes_read = 0;
+  ssize_t ret;
+  do {
+    ret = HANDLE_EINTR(read(shutdown_fd_,
+                            reinterpret_cast<char*>(&signal) + bytes_read,
+                            sizeof(signal) - bytes_read));
+    if (ret < 0) {
+      NOTREACHED() << "Unexpected error: " << strerror(errno);
+      ShutdownFDReadError();
+      break;
+    } else if (ret == 0) {
+      NOTREACHED() << "Unexpected closure of shutdown pipe.";
+      ShutdownFDClosedError();
+      break;
+    }
+    bytes_read += ret;
+  } while (bytes_read < sizeof(signal));
+  VLOG(1) << "Handling shutdown for signal " << signal << ".";
+
+  if (!task_runner_->PostTask(FROM_HERE, shutdown_callback_)) {

[James Cook, 2017/03/01 18:24:38]

Used it here.

+    // Without a valid task runner to post the exit task to, there aren't many
+    // options. Raise the signal again. The default handler will pick it up
+    // and cause an ungraceful exit.
+    RAW_LOG(WARNING, "No valid task runner, exiting ungracefully.");
+    kill(getpid(), signal);
+
+    // The signal may be handled on another thread.  Give that a chance to
+    // happen.
+    sleep(3);
+
+    // We really should be dead by now.  For whatever reason, we're not. Exit
+    // immediately, with the exit status set to the signal number with bit 8
+    // set.  On the systems that we care about, this exit status is what is
+    // normally used to indicate an exit by this signal's default handler.
+    // This mechanism isn't a de jure standard, but even in the worst case, it
+    // should at least result in an immediate exit.
+    RAW_LOG(WARNING, "Still here, exiting really ungracefully.");
+    _exit(signal | (1 << 7));
+  }
+  ExitPosted();
+}
+
+}  // namespace
+
+void InstallShutdownSignalHandlers(
+    const base::Closure& shutdown_callback,
+    const scoped_refptr<base::SingleThreadTaskRunner>& task_runner) {
+  int pipefd[2];
+  int ret = pipe(pipefd);
+  if (ret < 0) {
+    PLOG(DFATAL) << "Failed to create pipe";
+    return;

[James Cook, 2017/03/01 18:24:38]

Added early exit to reduce indenting.

+  }
+  g_pipe_pid = getpid();
+  g_shutdown_pipe_read_fd = pipefd[0];
+  g_shutdown_pipe_write_fd = pipefd[1];
+#if !defined(ADDRESS_SANITIZER) && !defined(KEEP_SHADOW_STACKS)
+  const size_t kShutdownDetectorThreadStackSize = PTHREAD_STACK_MIN * 2;
+#else
+  // ASan instrumentation and -finstrument-functions (used for keeping the
+  // shadow stacks) bloat the stack frames, so we need to increase the stack
+  // size to avoid hitting the guard page.
+  const size_t kShutdownDetectorThreadStackSize = PTHREAD_STACK_MIN * 4;
+#endif
+  ShutdownDetector* detector = new ShutdownDetector(

[James Cook, 2017/03/01 18:24:38]

Used local variable so I could add the leak annotation.

+      g_shutdown_pipe_read_fd, shutdown_callback, task_runner);
+  // PlatformThread does not delete its delegate.
+  ANNOTATE_LEAKING_OBJECT_PTR(detector);
+  if (!base::PlatformThread::CreateNonJoinable(kShutdownDetectorThreadStackSize,
+                                               detector)) {
+    LOG(DFATAL) << "Failed to create shutdown detector task.";
+  }
+
+  // Setup signal handlers for shutdown AFTER shutdown pipe is setup because
+  // it may be called right away after handler is set.
+
+  // If adding to this list of signal handlers, note the new signal probably
+  // needs to be reset in child processes. See
+  // base/process_util_posix.cc:LaunchProcess.
+
+  // We need to handle SIGTERM, because that is how many POSIX-based distros
+  // ask processes to quit gracefully at shutdown time.
+  struct sigaction action;
+  memset(&action, 0, sizeof(action));
+  action.sa_handler = SIGTERMHandler;
+  CHECK(sigaction(SIGTERM, &action, nullptr) == 0);
+
+  // Also handle SIGINT - when the user terminates the browser via Ctrl+C. If
+  // the browser process is being debugged, GDB will catch the SIGINT first.
+  action.sa_handler = SIGINTHandler;
+  CHECK(sigaction(SIGINT, &action, nullptr) == 0);
+
+  // And SIGHUP, for when the terminal disappears. On shutdown, many Linux
+  // distros send SIGHUP, SIGTERM, and then SIGKILL.
+  action.sa_handler = SIGHUPHandler;
+  CHECK(sigaction(SIGHUP, &action, nullptr) == 0);
+}