Unexpected EINVAL from pthread_join

Mon Feb 23 15:25:00 GMT 2015

On Feb 23 13:59, Corinna Vinschen wrote:
> On Feb 23 13:14, Corinna Vinschen wrote:
> > On Feb 22 22:54, Lasse Collin wrote:
> > > It seems that a signal can cause pthread_join to incorrectly return
> > > EINVAL. I debugged it only a little but hopefully someone finds this
> > > useful:
> > > 
> > > In the file thread.cc, function pthread::join, the call to cygwait may
> > > return WAIT_SIGNALED if a signal is sent to the process. The switch
> > > statement handling the return value assumes that only WAIT_OBJECT_0 and
> > > WAIT_CANCELED are possible. The default section of the switch statement
> > > has a comment "should never happen" and it returns EINVAL. It might be
> > > that the problem occurs only when SA_RESTART isn't used.
> [...]
> I looked into the Linux man page for pthread_join(1). It doesn't mention
> signals and EINTR at all. Then I looked into the SUSv4 pages(2) and it
> only has this to say:
>> The pthread_join() function shall not return an error code of [EINTR].
>> Searching further on this I found this(3):
>> The wait in pthread_join is not broken by a signal. If a thread
> waiting in pthread_join receives a signal that is not masked, if will
> execute the signal handler, and then return to waiting in
> pthread_join.
>> Taking that at face value, the following patch should do the right
> thing, doesn't it?

On second thought, this is not the right way to handle this. The
WAIT_SIGNALED is returned because we're in the main thread and
SA_RESTART is not set, as you assumed above. This leads to the
question why this scenario isn't handled directly in cygwait.
So what I did now is to apply the below patch to CVS. It adds a flag
cw_sig_restart to cygwait, which also restarts in the main thread if
SA_RESTART is not set, as it's supposed to be for pthread_join.
I uploaded a new developer snapshot to https://cygwin.com/snapshots/
Can you please test if it works as desired?
Thanks,
Corinna
 * cygwait.h (enum cw_wait_mask): Add cw_sig_restart. Add comments
 to explain the meaning of the possible values.
 * cygwait.cc (is_cw_sig_restart): Define.
 (is_cw_sig_handle): Check for cw_sig_restart as well.
 (cygwait): Restart always if cw_sig_restart is set.
 * thread.cc (pthread::join): Call cygwait with cw_sig_restart flag
 to avoid having to handle signals at all.
Index: cygwait.h
===================================================================
RCS file: /cvs/src/src/winsup/cygwin/cygwait.h,v
retrieving revision 1.10
diff -u -p -r1.10 cygwait.h

--- cygwait.h	9 Apr 2013 01:01:19 -0000	1.10
+++ cygwait.h	23 Feb 2015 13:54:48 -0000
@@ -1,7 +1,7 @@
 /* cygwait.h
 
- Copyright 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013
- Red Hat, Inc.
+ Copyright 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013,
+ 2015 Red Hat, Inc.
 
 This file is part of Cygwin.
 
@@ -16,11 +16,12 @@
 
 enum cw_wait_mask
 {
- cw_cancel =		0x0001,
- cw_cancel_self =	0x0002,
- cw_sig =		0x0004,
- cw_sig_eintr =	0x0008,
- cw_sig_cont =		0x0010
+ cw_cancel =		0x0001,	/* Cancellation point. Return to caller. */
+ cw_cancel_self =	0x0002,	/* Cancellation point. Cancel self. */
+ cw_sig =		0x0004,	/* Handle signals. */
+ cw_sig_eintr =	0x0008,	/* Caller handles signals. */
+ cw_sig_cont =		0x0010,	/* Caller handles SIGCONT. */
+ cw_sig_restart =	0x0020	/* Restart even if SA_RESTART isn't set. */
 };
 
 extern LARGE_INTEGER cw_nowait_storage;
Index: cygwait.cc
===================================================================
RCS file: /cvs/src/src/winsup/cygwin/cygwait.cc,v
retrieving revision 1.12
diff -u -p -r1.12 cygwait.cc
--- cygwait.cc	23 Feb 2015 13:32:16 -0000	1.12
+++ cygwait.cc	23 Feb 2015 13:54:48 -0000
@@ -18,8 +18,10 @@
 #define is_cw_sig		(mask & cw_sig)
 #define is_cw_sig_eintr		(mask & cw_sig_eintr)
 #define is_cw_sig_cont		(mask & cw_sig_cont)
+#define is_cw_sig_restart	(mask & cw_sig_restart)
 
-#define is_cw_sig_handle	(mask & (cw_sig | cw_sig_eintr | cw_sig_cont))
+#define is_cw_sig_handle	(mask & (cw_sig | cw_sig_eintr \
+					 | cw_sig_cont | cw_sig_restart))
 
 LARGE_INTEGER cw_nowait_storage;
 
@@ -88,7 +90,7 @@ cygwait (HANDLE object, PLARGE_INTEGER t
 	 continue;
 	 if (is_cw_sig_eintr || (is_cw_sig_cont && sig == SIGCONT))
 	 ;
-	 else if (_my_tls.call_signal_handler ())
+	 else if (_my_tls.call_signal_handler () || is_cw_sig_restart)
 	 continue;
 	 res = WAIT_SIGNALED;	/* caller will deal with signals */
 	}
Index: thread.cc
===================================================================
RCS file: /cvs/src/src/winsup/cygwin/thread.cc,v
retrieving revision 1.296
diff -u -p -r1.296 thread.cc
--- thread.cc	28 Nov 2014 20:46:13 -0000	1.296
+++ thread.cc	23 Feb 2015 13:54:48 -0000
@@ -1,7 +1,7 @@
 /* thread.cc: Locking and threading module functions
 
 Copyright 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008,
- 2009, 2010, 2011, 2012, 2013, 2014 Red Hat, Inc.
+ 2009, 2010, 2011, 2012, 2013, 2014, 2015 Red Hat, Inc.
 
 This file is part of Cygwin.
 
@@ -2399,7 +2399,8 @@ pthread::join (pthread_t *thread, void *
 (*thread)->attr.joinable = PTHREAD_CREATE_DETACHED;
 (*thread)->mutex.unlock ();
 
- switch (cygwait ((*thread)->win32_obj_id, cw_infinite, cw_sig | cw_cancel))
+ switch (cygwait ((*thread)->win32_obj_id, cw_infinite,
+		 cw_sig | cw_sig_restart | cw_cancel))
 	{
 	case WAIT_OBJECT_0:
 	 if (return_val)
-- 
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
Red Hat
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