[Mac] Do not forward graceful shutdown from child signal handlers.

chrome/browser/chrome_browser_main_posix.cc

Index: chrome/browser/chrome_browser_main_posix.cc
diff --git a/chrome/browser/chrome_browser_main_posix.cc b/chrome/browser/chrome_browser_main_posix.cc
index 1bb0f2c822d402de098e67c7164a37b818da5252..eff4911faf9751a92b2f627291201f747faec7f3 100644
--- a/chrome/browser/chrome_browser_main_posix.cc
+++ b/chrome/browser/chrome_browser_main_posix.cc
@@ -40,6 +40,12 @@ namespace {
 void SIGCHLDHandler(int signal) {
 }
 
+// The OSX fork() implementation can crash in the child process before
+// 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|.

[viettrungluu, 2013/02/25 23:15:06]

Could you include a reference to the bug(s)?

[Scott Hess - ex-Googler, 2013/02/25 23:20:46]

Done.

+pid_t g_pipe_pid = -1;
 int g_shutdown_pipe_write_fd = -1;
 int g_shutdown_pipe_read_fd = -1;
 
@@ -51,6 +57,7 @@ void GracefulShutdownHandler(int signal) {
   action.sa_handler = SIG_DFL;
   RAW_CHECK(sigaction(signal, &action, NULL) == 0);
 
+  RAW_CHECK(g_pipe_pid == getpid());
   RAW_CHECK(g_shutdown_pipe_write_fd != -1);
   RAW_CHECK(g_shutdown_pipe_read_fd != -1);
   size_t bytes_written = 0;
@@ -301,6 +308,7 @@ void ChromeBrowserMainPartsPosix::PostMainMessageLoopStart() {
   } else {
     g_shutdown_pipe_read_fd = pipefd[0];
     g_shutdown_pipe_write_fd = pipefd[1];
+    g_pipe_pid = getpid();

[viettrungluu, 2013/02/25 23:15:06]

Nit: You may as well initialize these in the same order as they're declared
(i.e., g_pipe_pid before the fds).

[Scott Hess - ex-Googler, 2013/02/25 23:20:46]

Done.

I was not willing to initialize the write fd before the read fd.  It looked too
weird.  Should have used a socketpair(), or just assumed that pipe() _is_ a
socketpair(), but  that would be creepy, too.

 #if !defined(ADDRESS_SANITIZER) && !defined(KEEP_SHADOW_STACKS)
     const size_t kShutdownDetectorThreadStackSize = PTHREAD_STACK_MIN;
 #else