From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from NAM12-BN8-obe.outbound.protection.outlook.com (mail-bn8nam12on2098.outbound.protection.outlook.com [40.107.237.98]) by sourceware.org (Postfix) with ESMTPS id 1B65A3857805 for ; Wed, 10 Nov 2021 14:47:35 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 1B65A3857805 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=Wx0UQMx/kQRVYrnlu7PrLGBESq3a4KYGC3WzbM1ibrm/1NeWON5Bi/j+aPNmU6IbNMCfsYXGardP4CPKfZqBRvle85sIsKHE9leFUhif62T26ECIIXnGjT/He9W2eq+rROb4TMVujhJf/1i7jnsbi/78Ys7Ljt7S4D7ZJKEIAMkKPctsiEtGkzeilaLMkCYJSh+CkgtQ5mCKBvP1FAlodmuQe+qEuv01rt2NhGiOeRdBacWQCkQgnreT/OPwN4cmTNGgotFYS4DkvXjWl4k76hGafp+kfolDKzyonmUJ6E2sBecapbjZt3xXo90Vzj4MxxKaFxjOJKCwAG27QqE6mg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=6gplGs7KSPyUBG7Rl66EkYcCg0OzHYlxDILW+iMLsHY=; b=Za+S5raIg/R0YcekqYmNR1kZ7zeF3cbbsbJwaJo1kCfyWxFgfuB+npkBs/9Q74PJTfTuSPZbpmenvoLbooo/Myp7kP7Q8hj0U8WdVD6CRwgoQLVvVu0nqiFg0JCoGBc2Vl0kmFxjaRfI29LFqsovAKwF/oY/BPRx2EfV7vg8oyBAL2KWtS9g7ilUx0TzpTYoLrOYLL1MLLDgwaaeJErsgQ3Hhl+Vy90d0v4Se15posIbZDyk8vd+cad1nGg2X4siFyNcEQdX3ghNlp3X0HgfQN+ulwABP64ul886WjQlS0ta/yqhmWP/6hxMEQebkMkmDYnk50k128x7mArlJ4Avow== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=cornell.edu; dmarc=pass action=none header.from=cornell.edu; dkim=pass header.d=cornell.edu; arc=none Received: from BN7PR04MB4388.namprd04.prod.outlook.com (2603:10b6:406:f8::19) by BN7PR04MB3842.namprd04.prod.outlook.com (2603:10b6:406:ce::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4690.16; Wed, 10 Nov 2021 14:47:33 +0000 Received: from BN7PR04MB4388.namprd04.prod.outlook.com ([fe80::88c4:79c5:1eb1:b969]) by BN7PR04MB4388.namprd04.prod.outlook.com ([fe80::88c4:79c5:1eb1:b969%7]) with mapi id 15.20.4669.016; Wed, 10 Nov 2021 14:47:33 +0000 Message-ID: <4b937b32-e348-19d2-2406-c55fa12e20a3@cornell.edu> Date: Wed, 10 Nov 2021 09:47:31 -0500 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0 Subject: Re: Another pipe-related problem? Content-Language: en-US To: cygwin@cygwin.com References: <05c4180e-396b-4af3-ac0c-2ab8125df17e@cornell.edu> <0971ace1-5ee8-bdcc-5fd9-4551b294ebf8@cornell.edu> <75197fd0-d5da-3236-a7df-b8ffc3f67da7@cornell.edu> From: Ken Brown In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: CH2PR10CA0009.namprd10.prod.outlook.com (2603:10b6:610:4c::19) To BN7PR04MB4388.namprd04.prod.outlook.com (2603:10b6:406:f8::19) MIME-Version: 1.0 Received: from [IPV6:2603:7081:7e3f:3419:7428:1d03:8434:f8fd] (2603:7081:7e3f:3419:7428:1d03:8434:f8fd) by CH2PR10CA0009.namprd10.prod.outlook.com (2603:10b6:610:4c::19) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4690.15 via Frontend Transport; Wed, 10 Nov 2021 14:47:32 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 9870d4d5-67ab-43a0-f508-08d9a4590749 X-MS-TrafficTypeDiagnostic: BN7PR04MB3842: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:6430; 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It finally occurred to me to stop looking for a bug in fhandler_pipe::raw_read and instead see if something is in fact repeatedly writing to the pipe, so that drain_signal_event_pipe never finishes. Putting a breakpoint at fhandler_pipe::raw_write, I found that this is in fact the case. While the main thread is repeatedly reading from the pipe, a second thread is repeatedly writing to it. Here's the backtrace of that thread: #0 fhandler_pipe_fifo::raw_write (this=0x18039f370, ptr=0x2c4ca3b, len=1) at ../../../../temp/winsup/cygwin/fhandler_pipe.cc:430 #1 0x000000018006f39a in fhandler_base::write (this=0x18039f370, ptr=0x2c4ca3b, len=1) at ../../../../temp/winsup/cygwin/fhandler.cc:907 #2 0x0000000180158fd1 in write (fd=4, ptr=0x2c4ca3b, len=1) at ../../../../temp/winsup/cygwin/syscalls.cc:1360 #3 0x00000001801b9b5b in _sigfe () at sigfe.s:35 #4 0x00000001006ae471 in retry_write_1 (fildes=4, buf=0x2c4ca3b, nbyte=1, allow_quit=0) at sysdep.c:2364 #5 0x00000001006ae581 in retry_write (fildes=4, buf=0x2c4ca3b, nbyte=1) at sysdep.c:2386 #6 0x00000001004b3ba5 in signal_fake_event () at event-unixoid.c:149 #7 0x0000000100691060 in alarm_signal (signo=14) at signal.c:559 #8 0x00000001006ec6e4 in mswindows_raise (nsig=14) at win32.c:694 #9 0x00000001006ec72d in setitimer_helper_proc (unused_uID=96, unused_uMsg=0, dwUser=14, unused_dw1=0, unused_dw2=0) at win32.c:742 #10 0x00007ffb363c2811 in WINMM!PlaySoundW () from /c/WINDOWS/SYSTEM32/WINMM.dll #11 0x000000018004771c in _cygtls::call2 (this=0x2c4ce00, func=0x7ffb363c26c0 , arg=0x0, buf=0x2c4cce0) at ../../../../temp/winsup/cygwin/cygtls.cc:40 #12 0x00000001800476c1 in _cygtls::call ( func=0x7ffb363c26c0 , arg=0x0) at ../../../../temp/winsup/cygwin/cygtls.cc:27 #13 0x00000001800e4f15 in threadfunc_fe (arg=0x0) at ../../../../temp/winsup/cygwin/init.cc:28 #14 0x00007ffb43da7034 in KERNEL32!BaseThreadInitThunk () from /c/WINDOWS/System32/KERNEL32.DLL #15 0x00007ffb448c2651 in ntdll!RtlUserThreadStart () from /c/WINDOWS/SYSTEM32/ntdll.dll #16 0x0000000000000000 in ?? () Backtrace stopped: previous frame inner to this frame (corrupt stack?) This looks to me like an XEmacs bug that happens to be triggered by the new pipe code, although maybe there's also a Cygwin bug that I'm not seeing. The comment at the beginning of signal_fake_event might be relevant: void signal_fake_event (void) { Rawbyte rbyte = 0; /* We do the write always. Formerly I tried to "optimize" this by setting a flag indicating whether we're blocking and only doing the write in that case, but there is a race condition if the signal occurs after we've checked for the signal occurrence (which could occur in many places throughout an iteration of the command loop, e.g. in status_notify()), but before we set the blocking flag. This should be OK as long as write() is reentrant, which I'm fairly sure it is since it's a system call. */ if (signal_event_pipe_initialized) /* In case a signal comes through while we're dumping */ { int old_errno = errno; retry_write (signal_event_pipe[1], &rbyte, 1); errno = old_errno; } } Ken