From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 26692 invoked by alias); 27 Apr 2009 14:37:05 -0000 Received: (qmail 26637 invoked by uid 22791); 27 Apr 2009 14:37:00 -0000 X-SWARE-Spam-Status: No, hits=-2.1 required=5.0 tests=AWL,BAYES_00,SPF_PASS X-Spam-Check-By: sourceware.org Received: from mail.codesourcery.com (HELO mail.codesourcery.com) (65.74.133.4) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 27 Apr 2009 14:36:55 +0000 Received: (qmail 30847 invoked from network); 27 Apr 2009 14:36:53 -0000 Received: from unknown (HELO rex.config) (julian@127.0.0.2) by mail.codesourcery.com with ESMTPA; 27 Apr 2009 14:36:53 -0000 Date: Mon, 27 Apr 2009 14:37:00 -0000 From: Julian Brown To: gdb-patches@sourceware.org Cc: gcc-patches@gcc.gnu.org, binutils@sourceware.org Subject: [PATCH, libiberty] Pex pipes block under win32 when parent process dies Message-ID: <20090427153649.53adf4f0@rex.config> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="MP_/H3H88XmRppw7ho=g4rI6dkb" X-IsSubscribed: yes Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org X-SW-Source: 2009-04/txt/msg00735.txt.bz2 --MP_/H3H88XmRppw7ho=g4rI6dkb Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Content-Disposition: inline Content-length: 1775 Hi, This patch addresses a problem where child processes started using the libiberty 'pex' mechanism could block indefinitely when trying to write to the parent if the parent exits unexpectedly. We (at CodeSourcery) observed this happening in gdb when starting a debug stub like so: (gdb) target remote | /path/to/stub ... though it's possible it could occur under other circumstances too (though I'm not sure which). In the above case, if gdb is killed using e.g. the task manager in Windows, the stub (which tries to output to stderr then fflush()) will block and fail to exit. The rationale behind the patch is borrowed from the MSDN page: http://msdn.microsoft.com/en-us/library/aa298531.aspx IIUC, at the moment, the child is spawned and inherits open descriptors for both ends of the pipe. Under Win32, you don't get EOF on a pipe until all of the copies of the write end of the pipe are closed, so that won't happen if the parent alone dies. The change in pex_win32_pipe() means that the child will get neither end of the pipe by default. So we duplicate the in/out/error descriptors in pex_win32_exec_child() to get inheritable versions to pass to the child, then close the originals. After spawning, we close the duplicates. Then since the parent ends up with no copies of the write end of the pipe, if it exits it won't cause the child to block. This seems to suffice to fix the problem described above. OK to apply to the Sourceware/GCC copies of libiberty? Cheers, Julian ChangeLog libiberty/ * pex-win32.c (pex_win32_pipe): Add _O_NOINHERIT. (pex_win32_exec_child): Ensure each process has only one handle open on pipe endpoints. Close standard input after creating child for symmetry with standard output/standard error. --MP_/H3H88XmRppw7ho=g4rI6dkb Content-Type: text/x-patch; name=pex-no-inherit-2.diff Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=pex-no-inherit-2.diff Content-length: 2363 Index: libiberty/pex-win32.c =================================================================== --- libiberty/pex-win32.c (revision 246292) +++ libiberty/pex-win32.c (working copy) @@ -730,7 +730,7 @@ spawn_script (const char *executable, ch /* Execute a child. */ static pid_t -pex_win32_exec_child (struct pex_obj *obj ATTRIBUTE_UNUSED, int flags, +pex_win32_exec_child (struct pex_obj *obj, int flags, const char *executable, char * const * argv, char* const* env, int in, int out, int errdes, @@ -746,6 +746,25 @@ pex_win32_exec_child (struct pex_obj *ob OSVERSIONINFO version_info; STARTUPINFO si; PROCESS_INFORMATION pi; + int orig_out, orig_in, orig_err; + BOOL separate_stderr = !(flags & PEX_STDERR_TO_STDOUT); + + /* Ensure we have inheritable descriptors to pass to the child, and close the + original descriptors. */ + orig_in = in; + in = _dup (orig_in); + obj->funcs->close (obj, orig_in); + + orig_out = out; + out = _dup (orig_out); + obj->funcs->close (obj, orig_out); + + if (separate_stderr) + { + orig_err = errdes; + errdes = _dup (orig_err); + obj->funcs->close (obj, orig_err); + } stdin_handle = INVALID_HANDLE_VALUE; stdout_handle = INVALID_HANDLE_VALUE; @@ -753,7 +772,7 @@ pex_win32_exec_child (struct pex_obj *ob stdin_handle = (HANDLE) _get_osfhandle (in); stdout_handle = (HANDLE) _get_osfhandle (out); - if (!(flags & PEX_STDERR_TO_STDOUT)) + if (separate_stderr) stderr_handle = (HANDLE) _get_osfhandle (errdes); else stderr_handle = stdout_handle; @@ -822,8 +841,11 @@ pex_win32_exec_child (struct pex_obj *ob *errmsg = "CreateProcess"; } - /* Close the standard output and standard error handles in the - parent. */ + /* Close the standard input, standard output and standard error handles + in the parent. */ + + if (in != STDIN_FILENO) + obj->funcs->close (obj, in); if (out != STDOUT_FILENO) obj->funcs->close (obj, out); if (errdes != STDERR_FILENO) @@ -883,7 +905,7 @@ static int pex_win32_pipe (struct pex_obj *obj ATTRIBUTE_UNUSED, int *p, int binary) { - return _pipe (p, 256, binary ? _O_BINARY : _O_TEXT); + return _pipe (p, 256, (binary ? _O_BINARY : _O_TEXT) | _O_NOINHERIT); } /* Get a FILE pointer to read from a file descriptor. */ --MP_/H3H88XmRppw7ho=g4rI6dkb--