Index: base/process_util_mac.mm |
=================================================================== |
--- base/process_util_mac.mm (revision 111236) |
+++ base/process_util_mac.mm (working copy) |
@@ -7,6 +7,7 @@ |
#import <Cocoa/Cocoa.h> |
#include <crt_externs.h> |
#include <dlfcn.h> |
+#include <errno.h> |
#include <mach/mach.h> |
#include <mach/mach_init.h> |
#include <mach/mach_vm.h> |
@@ -16,7 +17,9 @@ |
#include <mach-o/nlist.h> |
#include <malloc/malloc.h> |
#import <objc/runtime.h> |
+#include <signal.h> |
#include <spawn.h> |
+#include <sys/event.h> |
#include <sys/mman.h> |
#include <sys/sysctl.h> |
#include <sys/types.h> |
@@ -27,6 +30,7 @@ |
#include "base/debug/debugger.h" |
#include "base/eintr_wrapper.h" |
+#include "base/file_util.h" |
#include "base/hash_tables.h" |
#include "base/logging.h" |
#include "base/mac/mac_util.h" |
@@ -990,4 +994,159 @@ |
return info.kp_eproc.e_ppid; |
} |
+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. |
+ TimeDelta remaining_delta = TimeDelta::FromSeconds(timeout); |
+ Time deadline = 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 - 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 EnsureProcessTerminated(ProcessHandle process) { |
+ WaitForChildToDie(process, kWaitBeforeKillSeconds); |
+} |
+ |
} // namespace base |