From: dick.r.chiang@gmail.com
To: Andreas Politz <politza@hochschule-trier.de>
Cc: 36609@debbugs.gnu.org
Subject: bug#36609: 27.0.50; Possible race-condition in threading implementation
Date: Sun, 06 Jun 2021 11:50:06 -0400 [thread overview]
Message-ID: <87k0n73scx.fsf@dick> (raw)
In-Reply-To: <87muhks3b5.fsf@hochschule-trier.de> (Andreas Politz's message of "Thu, 11 Jul 2019 22:51:10 +0200")
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Four attachments:
#1. Want to revert commit 9c62ffb
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From 01b8b847f5fc4b65eaac06c7c2d85f8c5410c497 Mon Sep 17 00:00:00 2001
From: dickmao <none>
Date: Sun, 6 Jun 2021 11:10:13 -0400
Subject: [PATCH] Revert "Fix lock failures in xg_select"
This reverts commit 9c62ffb08262c82b7e38e6eb5767f2087424aa47.
* src/thread.c (really_call_select): revert 9c62ffb
* src/xgselect.c (xg_select): revert 9c62ffb
---
src/thread.c | 8 --------
src/xgselect.c | 42 ++++++++++++++----------------------------
src/xgselect.h | 2 --
3 files changed, 14 insertions(+), 38 deletions(-)
diff --git a/src/thread.c b/src/thread.c
index f74f611148..609cd7c5fc 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -28,12 +28,6 @@ Copyright (C) 2012-2021 Free Software Foundation, Inc.
#include "pdumper.h"
#include "keyboard.h"
-#if defined HAVE_GLIB && ! defined (HAVE_NS)
-#include <xgselect.h>
-#else
-#define release_select_lock() do { } while (0)
-#endif
-
union aligned_thread_state
{
struct thread_state s;
@@ -592,8 +586,6 @@ really_call_select (void *arg)
sa->result = (sa->func) (sa->max_fds, sa->rfds, sa->wfds, sa->efds,
sa->timeout, sa->sigmask);
- release_select_lock ();
-
block_interrupt_signal (&oldset);
/* If we were interrupted by C-g while inside sa->func above, the
signal handler could have called maybe_reacquire_global_lock, in
diff --git a/src/xgselect.c b/src/xgselect.c
index 0d91d55bad..d7c63e3be1 100644
--- a/src/xgselect.c
+++ b/src/xgselect.c
@@ -29,27 +29,6 @@ Copyright (C) 2009-2021 Free Software Foundation, Inc.
#include "blockinput.h"
#include "systime.h"
-static ptrdiff_t threads_holding_glib_lock;
-static GMainContext *glib_main_context;
-
-void release_select_lock (void)
-{
- if (--threads_holding_glib_lock == 0)
- g_main_context_release (glib_main_context);
-}
-
-static void acquire_select_lock (GMainContext *context)
-{
- if (threads_holding_glib_lock++ == 0)
- {
- glib_main_context = context;
- while (!g_main_context_acquire (context))
- {
- /* Spin. */
- }
- }
-}
-
/* `xg_select' is a `pselect' replacement. Why do we need a separate function?
1. Timeouts. Glib and Gtk rely on timer events. If we did pselect
with a greater timeout then the one scheduled by Glib, we would
@@ -75,19 +54,26 @@ xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
GPollFD *gfds = gfds_buf;
int gfds_size = ARRAYELTS (gfds_buf);
int n_gfds, retval = 0, our_fds = 0, max_fds = fds_lim - 1;
+ bool context_acquired = false;
int i, nfds, tmo_in_millisec, must_free = 0;
bool need_to_dispatch;
context = g_main_context_default ();
- acquire_select_lock (context);
+ context_acquired = g_main_context_acquire (context);
+ /* FIXME: If we couldn't acquire the context, we just silently proceed
+ because this function handles more than just glib file descriptors.
+ Note that, as implemented, this failure is completely silent: there is
+ no feedback to the caller. */
if (rfds) all_rfds = *rfds;
else FD_ZERO (&all_rfds);
if (wfds) all_wfds = *wfds;
else FD_ZERO (&all_wfds);
- n_gfds = g_main_context_query (context, G_PRIORITY_LOW, &tmo_in_millisec,
- gfds, gfds_size);
+ n_gfds = (context_acquired
+ ? g_main_context_query (context, G_PRIORITY_LOW, &tmo_in_millisec,
+ gfds, gfds_size)
+ : -1);
if (gfds_size < n_gfds)
{
@@ -165,10 +151,8 @@ xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
#else
need_to_dispatch = true;
#endif
- if (need_to_dispatch)
+ if (need_to_dispatch && context_acquired)
{
- acquire_select_lock (context);
-
int pselect_errno = errno;
/* Prevent g_main_dispatch recursion, that would occur without
block_input wrapper, because event handlers call
@@ -178,9 +162,11 @@ xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
g_main_context_dispatch (context);
unblock_input ();
errno = pselect_errno;
- release_select_lock ();
}
+ if (context_acquired)
+ g_main_context_release (context);
+
/* To not have to recalculate timeout, return like this. */
if ((our_fds > 0 || (nfds == 0 && tmop == &tmo)) && (retval == 0))
{
diff --git a/src/xgselect.h b/src/xgselect.h
index 2142a236b2..e00dce1283 100644
--- a/src/xgselect.h
+++ b/src/xgselect.h
@@ -29,6 +29,4 @@ #define XGSELECT_H
fd_set *rfds, fd_set *wfds, fd_set *efds,
struct timespec *timeout, sigset_t *sigmask);
-extern void release_select_lock (void);
-
#endif /* XGSELECT_H */
--
2.26.2
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#2. Fails on tip of master, succeeds after patch in #1.
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#3. Abridged original example, fails after patch in #1.
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Fails not necessarily because xgselect.c is wrong, but rather because
channel-recv blocks on a mutex before channel-send can get its act together.
This was hard for all to discern because OP seemed to have gone out of his way
to obfuscate his "minimum" example.
#4. What #3 probably intended, succeeds after patch in #1.
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next prev parent reply other threads:[~2021-06-06 15:50 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-11 20:51 bug#36609: 27.0.50; Possible race-condition in threading implementation Andreas Politz
2019-07-12 7:47 ` Eli Zaretskii
2019-07-12 8:05 ` Eli Zaretskii
2019-07-12 9:02 ` Pip Cet
2019-07-12 12:42 ` Eli Zaretskii
2019-07-12 12:57 ` Pip Cet
2019-07-12 13:31 ` Eli Zaretskii
2019-07-12 13:51 ` Pip Cet
2019-07-12 15:05 ` Eli Zaretskii
2019-07-12 18:06 ` Pip Cet
2019-07-12 18:27 ` Eli Zaretskii
2019-07-12 18:34 ` Eli Zaretskii
2019-07-12 19:24 ` Pip Cet
2019-07-12 19:57 ` Eli Zaretskii
2019-07-13 14:37 ` Pip Cet
2019-07-13 15:03 ` Eli Zaretskii
2019-07-13 15:13 ` Eli Zaretskii
2019-07-13 15:54 ` Eli Zaretskii
2019-07-13 15:57 ` Pip Cet
2019-07-13 16:02 ` Eli Zaretskii
2019-07-13 18:17 ` Pip Cet
2020-08-21 12:57 ` Lars Ingebrigtsen
2019-07-13 15:04 ` Andreas Politz
2019-07-12 12:44 ` Pip Cet
2019-07-12 12:55 ` Eli Zaretskii
2019-07-12 13:40 ` Pip Cet
2019-07-12 13:51 ` Eli Zaretskii
2019-07-12 14:34 ` Pip Cet
2019-07-12 15:02 ` Eli Zaretskii
2019-07-12 19:30 ` Pip Cet
2019-07-13 6:50 ` Eli Zaretskii
2021-06-06 15:50 ` dick.r.chiang [this message]
[not found] ` <87fsxv8182.fsf@dick>
2021-06-06 16:35 ` Eli Zaretskii
2021-06-06 19:10 ` dick.r.chiang
2021-06-06 19:27 ` Eli Zaretskii
2021-06-09 21:40 ` dick.r.chiang
2021-06-10 6:46 ` Eli Zaretskii
2021-06-10 11:52 ` dick.r.chiang
2021-06-10 14:18 ` Eli Zaretskii
2021-06-10 14:55 ` dick.r.chiang
2021-06-10 15:04 ` Eli Zaretskii
2021-06-10 21:36 ` dick.r.chiang
2021-06-11 6:00 ` Eli Zaretskii
2021-06-19 17:53 ` Eli Zaretskii
2021-06-19 19:14 ` dick.r.chiang
2021-06-19 19:18 ` Eli Zaretskii
2021-06-19 21:12 ` dick.r.chiang
2021-06-20 11:39 ` Eli Zaretskii
2021-06-20 14:01 ` dick.r.chiang
2021-06-20 15:53 ` Eli Zaretskii
2021-06-25 13:54 ` Eli Zaretskii
2021-06-10 15:35 ` Andreas Schwab
2021-06-10 15:39 ` Eli Zaretskii
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