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* [Bug stdio/27602] New: fflush(NULL) hangs when getc() ongoing
@ 2021-03-18 10:59 samuel.thibault@ens-lyon.org
2021-03-18 11:23 ` [Bug stdio/27602] " schwab@linux-m68k.org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: samuel.thibault@ens-lyon.org @ 2021-03-18 10:59 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=27602
Bug ID: 27602
Summary: fflush(NULL) hangs when getc() ongoing
Product: glibc
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: stdio
Assignee: unassigned at sourceware dot org
Reporter: samuel.thibault@ens-lyon.org
Target Milestone: ---
Created attachment 13320
--> https://sourceware.org/bugzilla/attachment.cgi?id=13320&action=edit
testcase
Hello,
The attached testcase hangs: a thread is blocked in getc(stdin), and the main
thread tries to call fflush(NULL), but that tries to lock stdin, and that's
already locked by getc, and thus cannot proceed.
Samuel
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* [Bug stdio/27602] fflush(NULL) hangs when getc() ongoing
2021-03-18 10:59 [Bug stdio/27602] New: fflush(NULL) hangs when getc() ongoing samuel.thibault@ens-lyon.org
@ 2021-03-18 11:23 ` schwab@linux-m68k.org
2021-03-18 11:28 ` samuel.thibault@ens-lyon.org
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: schwab@linux-m68k.org @ 2021-03-18 11:23 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=27602
--- Comment #1 from Andreas Schwab <schwab@linux-m68k.org> ---
And that's a bug why?
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* [Bug stdio/27602] fflush(NULL) hangs when getc() ongoing
2021-03-18 10:59 [Bug stdio/27602] New: fflush(NULL) hangs when getc() ongoing samuel.thibault@ens-lyon.org
2021-03-18 11:23 ` [Bug stdio/27602] " schwab@linux-m68k.org
@ 2021-03-18 11:28 ` samuel.thibault@ens-lyon.org
2021-03-18 11:45 ` schwab@linux-m68k.org
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: samuel.thibault@ens-lyon.org @ 2021-03-18 11:28 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=27602
--- Comment #2 from Samuel Thibault <samuel.thibault@ens-lyon.org> ---
Well, that is very surprising: fflush is supposed to flush the output, not
interfere with input.
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* [Bug stdio/27602] fflush(NULL) hangs when getc() ongoing
2021-03-18 10:59 [Bug stdio/27602] New: fflush(NULL) hangs when getc() ongoing samuel.thibault@ens-lyon.org
2021-03-18 11:23 ` [Bug stdio/27602] " schwab@linux-m68k.org
2021-03-18 11:28 ` samuel.thibault@ens-lyon.org
@ 2021-03-18 11:45 ` schwab@linux-m68k.org
2021-03-18 11:54 ` samuel.thibault@ens-lyon.org
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: schwab@linux-m68k.org @ 2021-03-18 11:45 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=27602
--- Comment #3 from Andreas Schwab <schwab@linux-m68k.org> ---
But fflush(NULL) needs to inspect each and every stream, in a thread safe way.
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* [Bug stdio/27602] fflush(NULL) hangs when getc() ongoing
2021-03-18 10:59 [Bug stdio/27602] New: fflush(NULL) hangs when getc() ongoing samuel.thibault@ens-lyon.org
` (2 preceding siblings ...)
2021-03-18 11:45 ` schwab@linux-m68k.org
@ 2021-03-18 11:54 ` samuel.thibault@ens-lyon.org
2021-03-18 12:01 ` schwab@linux-m68k.org
2021-03-18 12:07 ` samuel.thibault@ens-lyon.org
5 siblings, 0 replies; 7+ messages in thread
From: samuel.thibault@ens-lyon.org @ 2021-03-18 11:54 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=27602
--- Comment #4 from Samuel Thibault <samuel.thibault@ens-lyon.org> ---
Sure, I understand why technically it does hang, but it is still surprising to
see that it would block just because a getc is ongoing. If it was a write on a
pipe which is full, that wouldn't be surprising.
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* [Bug stdio/27602] fflush(NULL) hangs when getc() ongoing
2021-03-18 10:59 [Bug stdio/27602] New: fflush(NULL) hangs when getc() ongoing samuel.thibault@ens-lyon.org
` (3 preceding siblings ...)
2021-03-18 11:54 ` samuel.thibault@ens-lyon.org
@ 2021-03-18 12:01 ` schwab@linux-m68k.org
2021-03-18 12:07 ` samuel.thibault@ens-lyon.org
5 siblings, 0 replies; 7+ messages in thread
From: schwab@linux-m68k.org @ 2021-03-18 12:01 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=27602
--- Comment #5 from Andreas Schwab <schwab@linux-m68k.org> ---
The stream is locked, so no other thread can use it.
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* [Bug stdio/27602] fflush(NULL) hangs when getc() ongoing
2021-03-18 10:59 [Bug stdio/27602] New: fflush(NULL) hangs when getc() ongoing samuel.thibault@ens-lyon.org
` (4 preceding siblings ...)
2021-03-18 12:01 ` schwab@linux-m68k.org
@ 2021-03-18 12:07 ` samuel.thibault@ens-lyon.org
5 siblings, 0 replies; 7+ messages in thread
From: samuel.thibault@ens-lyon.org @ 2021-03-18 12:07 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=27602
Samuel Thibault <samuel.thibault@ens-lyon.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |NOTABUG
Status|NEW |RESOLVED
--- Comment #6 from Samuel Thibault <samuel.thibault@ens-lyon.org> ---
> The stream is locked
“
All functions that reference ( FILE *) objects shall behave as if they use
flockfile() and funlockfile() internally to obtain ownership of these (FILE *)
objects.
”
Ah, alright then.
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end of thread, other threads:[~2021-03-18 12:07 UTC | newest]
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2021-03-18 10:59 [Bug stdio/27602] New: fflush(NULL) hangs when getc() ongoing samuel.thibault@ens-lyon.org
2021-03-18 11:23 ` [Bug stdio/27602] " schwab@linux-m68k.org
2021-03-18 11:28 ` samuel.thibault@ens-lyon.org
2021-03-18 11:45 ` schwab@linux-m68k.org
2021-03-18 11:54 ` samuel.thibault@ens-lyon.org
2021-03-18 12:01 ` schwab@linux-m68k.org
2021-03-18 12:07 ` samuel.thibault@ens-lyon.org
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