POSIX: don't spawn zombies.

chrome/common/process_watcher_posix.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 "chrome/common/process_watcher.h"
+
+#include <errno.h>
+#include <signal.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#include "base/platform_thread.h"
+
+// Return true if the given child is dead. This will also reap the process.
+// Doesn't block.
+static bool IsChildDead(pid_t child) {
+  const int result = waitpid(child, NULL, WNOHANG);
+  if (result == -1) {
+    NOTREACHED();
+  } else if (result > 0) {
+    // The child has died.
+    return true;
+  }
+
+  return false;
+}
+
+// A thread class which waits for the given child to exit and reaps it.
+// If the child doesn't exit within a couple of seconds, kill it.
+class BackgroundReaper : public PlatformThread::Delegate {
+ public:
+  explicit BackgroundReaper(pid_t child)
+      : child_(child) {
+  }
+
+  void ThreadMain() {
+    WaitForChildToDie();
+    delete this;
+  }
+
+  void WaitForChildToDie() {
+    // There's no good way to wait for a specific child to exit in a timed
+    // fashion. (No kqueue on Linux), so we just loop and sleep.
+
+    // Waits 0.5 * 4 = 2 seconds.
+    for (unsigned i = 0; i < 4; ++i) {
+      PlatformThread::Sleep(500);  // 0.5 seconds
+      if (IsChildDead(child_))
+        return;
+    }
+
+    if (kill(child_, SIGKILL) == 0) {
+      // SIGKILL is uncatchable. Since the signal was delivered, we can
+      // just wait for the process to die now in a blocking manner.
+      int result;
+      do {
+        result = waitpid(child_, NULL, 0);
+      } while (result == -1 && errno == EINTR);
+    } else {
+      LOG(ERROR) << "While waiting for " << child_ << " to terminate we"
+                 << " failed to deliver a SIGKILL signal (" << errno << ").";
+    }
+  }
+
+ private:
+  const pid_t child_;
+
+  DISALLOW_COPY_AND_ASSIGN(BackgroundReaper);
+};
+
+// static
+void ProcessWatcher::EnsureProcessTerminated(base::ProcessHandle process) {
+  // If the child is already dead, then there's nothing to do
+  if (IsChildDead(process))
+    return;
+
+  BackgroundReaper* reaper = new BackgroundReaper(process);
+  PlatformThread::CreateNonJoinable(0, reaper);
+}