1 files changed, 170 insertions, 0 deletions
diff --git a/content/common/process_watcher_mac.cc b/content/common/process_watcher_mac.cc
new file mode 100644
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--- /dev/null
+++ b/content/common/process_watcher_mac.cc
@@ -0,0 +1,170 @@
+// 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) {
+    PLOG(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) {
+    PLOG(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) {
+        PLOG(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) {
+        PLOG(ERROR) << "kevent (wait " << child << ")";
+      } else if (result > 1) {
+        LOG(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 {
+          LOG(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) {
+    PLOG(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);
+}