Move the ProcessWatcher methods out of content/common/process_watcher into base/process_util, alo...

content/common/process_watcher_mac.cc

-// Copyright (c) 2009 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 "content/common/process_watcher.h"
-
-#include <errno.h>
-#include <signal.h>
-#include <sys/event.h>
-#include <sys/types.h>
-#include <sys/wait.h>
-
-#include "base/eintr_wrapper.h"
-#include "base/file_util.h"
-#include "base/time.h"
-
-namespace {
-
-const int kWaitBeforeKillSeconds = 2;
-
-// Reap |child| process. This call blocks until completion.
-void BlockingReap(pid_t child) {
-  const pid_t result = HANDLE_EINTR(waitpid(child, NULL, 0));
-  if (result == -1) {
-    DPLOG(ERROR) << "waitpid(" << child << ", NULL, 0)";
-  }
-}
-
-// Waits for |timeout| seconds for the given |child| to exit and reap it. If
-// the child doesn't exit within the time specified, kills it.
-//
-// This function takes two approaches: first, it tries to use kqueue to
-// observe when the process exits. kevent can monitor a kqueue with a
-// timeout, so this method is preferred to wait for a specified period of
-// time. Once the kqueue indicates the process has exited, waitpid will reap
-// the exited child. If the kqueue doesn't provide an exit event notification,
-// before the timeout expires, or if the kqueue fails or misbehaves, the
-// process will be mercilessly killed and reaped.
-//
-// A child process passed to this function may be in one of several states:
-// running, terminated and not yet reaped, and (apparently, and unfortunately)
-// terminated and already reaped. Normally, a process will at least have been
-// asked to exit before this function is called, but this is not required.
-// If a process is terminating and unreaped, there may be a window between the
-// time that kqueue will no longer recognize it and when it becomes an actual
-// zombie that a non-blocking (WNOHANG) waitpid can reap. This condition is
-// detected when kqueue indicates that the process is not running and a
-// non-blocking waitpid fails to reap the process but indicates that it is
-// still running. In this event, a blocking attempt to reap the process
-// collects the known-dying child, preventing zombies from congregating.
-//
-// In the event that the kqueue misbehaves entirely, as it might under a
-// EMFILE condition ("too many open files", or out of file descriptors), this
-// function will forcibly kill and reap the child without delay. This
-// eliminates another potential zombie vector. (If you're out of file
-// descriptors, you're probably deep into something else, but that doesn't
-// mean that zombies be allowed to kick you while you're down.)
-//
-// The fact that this function seemingly can be called to wait on a child
-// that's not only already terminated but already reaped is a bit of a
-// problem: a reaped child's pid can be reclaimed and may refer to a distinct
-// process in that case. The fact that this function can seemingly be called
-// to wait on a process that's not even a child is also a problem: kqueue will
-// work in that case, but waitpid won't, and killing a non-child might not be
-// the best approach.
-void WaitForChildToDie(pid_t child, int timeout) {
-  DCHECK(child > 0);
-  DCHECK(timeout > 0);
-
-  // DON'T ADD ANY EARLY RETURNS TO THIS FUNCTION without ensuring that
-  // |child| has been reaped. Specifically, even if a kqueue, kevent, or other
-  // call fails, this function should fall back to the last resort of trying
-  // to kill and reap the process. Not observing this rule will resurrect
-  // zombies.
-
-  int result;
-
-  int kq = HANDLE_EINTR(kqueue());
-  if (kq == -1) {
-    DPLOG(ERROR) << "kqueue()";
-  } else {
-    file_util::ScopedFD auto_close_kq(&kq);
-
-    struct kevent change = {0};
-    EV_SET(&change, child, EVFILT_PROC, EV_ADD, NOTE_EXIT, 0, NULL);
-    result = HANDLE_EINTR(kevent(kq, &change, 1, NULL, 0, NULL));
-
-    if (result == -1) {
-      if (errno != ESRCH) {
-        DPLOG(ERROR) << "kevent (setup " << child << ")";
-      } else {
-        // At this point, one of the following has occurred:
-        // 1. The process has died but has not yet been reaped.
-        // 2. The process has died and has already been reaped.
-        // 3. The process is in the process of dying. It's no longer
-        //    kqueueable, but it may not be waitable yet either. Mark calls
-        //    this case the "zombie death race".
-
-        result = HANDLE_EINTR(waitpid(child, NULL, WNOHANG));
-
-        if (result != 0) {
-          // A positive result indicates case 1. waitpid succeeded and reaped
-          // the child. A result of -1 indicates case 2. The child has already
-          // been reaped. In both of these cases, no further action is
-          // necessary.
-          return;
-        }
-
-        // |result| is 0, indicating case 3. The process will be waitable in
-        // short order. Fall back out of the kqueue code to kill it (for good
-        // measure) and reap it.
-      }
-    } else {
-      // Keep track of the elapsed time to be able to restart kevent if it's
-      // interrupted.
-      base::TimeDelta remaining_delta = base::TimeDelta::FromSeconds(timeout);
-      base::Time deadline = base::Time::Now() + remaining_delta;
-      result = -1;
-      struct kevent event = {0};
-      while (remaining_delta.InMilliseconds() > 0) {
-        const struct timespec remaining_timespec = remaining_delta.ToTimeSpec();
-        result = kevent(kq, NULL, 0, &event, 1, &remaining_timespec);
-        if (result == -1 && errno == EINTR) {
-          remaining_delta = deadline - base::Time::Now();
-          result = 0;
-        } else {
-          break;
-        }
-      }
-
-      if (result == -1) {
-        DPLOG(ERROR) << "kevent (wait " << child << ")";
-      } else if (result > 1) {
-        DLOG(ERROR) << "kevent (wait " << child << "): unexpected result "
-                    << result;
-      } else if (result == 1) {
-        if ((event.fflags & NOTE_EXIT) &&
-            (event.ident == static_cast<uintptr_t>(child))) {
-          // The process is dead or dying. This won't block for long, if at
-          // all.
-          BlockingReap(child);
-          return;
-        } else {
-          DLOG(ERROR) << "kevent (wait " << child
-                      << "): unexpected event: fflags=" << event.fflags
-                      << ", ident=" << event.ident;
-        }
-      }
-    }
-  }
-
-  // The child is still alive, or is very freshly dead. Be sure by sending it
-  // a signal. This is safe even if it's freshly dead, because it will be a
-  // zombie (or on the way to zombiedom) and kill will return 0 even if the
-  // signal is not delivered to a live process.
-  result = kill(child, SIGKILL);
-  if (result == -1) {
-    DPLOG(ERROR) << "kill(" << child << ", SIGKILL)";
-  } else {
-    // The child is definitely on the way out now. BlockingReap won't need to
-    // wait for long, if at all.
-    BlockingReap(child);
-  }
-}
-
-}  // namespace
-
-void ProcessWatcher::EnsureProcessTerminated(base::ProcessHandle process) {
-  WaitForChildToDie(process, kWaitBeforeKillSeconds);
-}