Re: [PATCH] libgfortran: Fix and simplify IO locking [PR92836]

[Thomas Koenig <tkoenig@netcologne.de>]

Hi Janne,

> Simplify IO locking in libgfortran.  The new IO implementation avoids
> accessing units without locks, as seen in PR 92836.  It also avoids
> lock inversion (except for a corner case wrt namelist query when
> reading from stdin and outputting to stdout), making it easier to
> verify correctness with tools like valgrind or threadsanitizer.  It is
> also simplified as the waiting and closed variables are not needed
> anymore, making it easier to understand and analyze.
> 
> Regtested on x86_64-pc-linux-gnu, Ok for master?

Sorry it took me so long to actually look at this. The patch for
PR 93599 took a bit longer than anticipated...

With your patch on top of the one I just submitted, I get
valgrind errors for the asynchronous I/O tests:

$ gfortran -g async_io_1.f90 -pthread
$ valgrind --tool=drd ./a.out
==22685== drd, a thread error detector
==22685== Copyright (C) 2006-2017, and GNU GPL'd, by Bart Van Assche.
==22685== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==22685== Command: ./a.out
==22685==
==22685== Destroying locked mutex: mutex 0x60708f0, recursion count 1, 
owner 1.
==22685==    at 0x4C37B65: pthread_mutex_destroy_intercept 
(drd_pthread_intercepts.c:865)
==22685==    by 0x4C37B65: pthread_mutex_destroy 
(drd_pthread_intercepts.c:875)
==22685==    by 0x50A6CAE: __gthread_mutex_destroy (gthr-default.h:740)
==22685==    by 0x50A6CAE: destroy_unit_mutex (unit.c:253)
==22685==    by 0x50A6CAE: close_unit_1 (unit.c:732)
==22685==    by 0x5091E67: _gfortran_st_close (close.c:108)
==22685==    by 0x4011D3: MAIN__ (async_io_1.f90:25)
==22685==    by 0x401AA9: main (async_io_1.f90:48)
==22685== mutex 0x60708f0 was first observed at:
==22685==    at 0x4C37FD5: pthread_mutex_lock_intercept 
(drd_pthread_intercepts.c:885)
==22685==    by 0x4C37FD5: pthread_mutex_lock (drd_pthread_intercepts.c:898)
==22685==    by 0x50A6039: __gthread_mutex_lock (gthr-default.h:749)
==22685==    by 0x50A6039: insert_unit (unit.c:241)
==22685==    by 0x50A615F: get_gfc_unit (unit.c:353)
==22685==    by 0x509DC93: _gfortran_st_open (open.c:889)
==22685==    by 0x400E4A: MAIN__ (async_io_1.f90:16)
==22685==    by 0x401AA9: main (async_io_1.f90:48)

(plus a few more).  I am currently bootstrapping without the patch
above so I can be sure that this is not an artifact.

However, it looks as if the "locked" argument to close_unit_1 gets
passed the wrong value somehow.  Could you maybe look at that?

Regards

	Thomas