* Re: gdb.threads/sigthread.c
2008-02-18 14:19 gdb.threads/sigthread.c Mark Kettenis
@ 2008-02-19 18:03 ` Jim Blandy
0 siblings, 0 replies; 2+ messages in thread
From: Jim Blandy @ 2008-02-19 18:03 UTC (permalink / raw)
To: Mark Kettenis; +Cc: gdb
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On Feb 18, 2008 1:03 AM, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
> You recently changed gdb.threads/sigthread.c to use barriers.
> Unfortunately the pthread_barrier_xxx() interfaces are not found in
> the standard POSIX threads standard, but part of the Advanced Realtime
> Threads POSIX extension. Therefore they are not widely available.
Yeah, I mentioned this concern when I posted the patch. I guess we know now.
> Could you change the test to use a more standard synchronisation
> mechanism? I guess having a global variable of type volatile
> sig_atomic_t, setting it to a non-zero value in main() (after the
> threads have been created) and checking the value in child_two() and
> thread_function() (perhaps calling sched_yield() if the variables
> isn't set yet) would do the trick.
I'll bet this isn't the only test in the test suite that would like
some barriers. How does the attached look?
> I can roll you a diff to do this if you want, but I don't think I have
> access to a system that shows the problem you tried to fix.
I developed the fix on a Core 2 Duo laptop running Linux, running
'while true; do :;done' in a few windows while running the test over
and over again as 'while runtest sigthread.exp; do :;done'. Or
something like that. It sometimes took a half-dozen iterations or so,
but it would fail eventually.
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gdb/testsuite/ChangeLog:
2008-02-19 Jim Blandy <jimb@red-bean.com>
* gdb.threads/gdb-barrier.c, gdb.threads/gdb-barrier.h: New files.
* gdb.threads/sigthread.c: Use the gdb barrier, not the POSIX
barriers, which are optional.
* gdb.threads/sigthread.exp: Link the program with gdb-barrier.c.
diff -r b72cf86f9dad gdb/testsuite/gdb.threads/gdb-barrier.c
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/gdb/testsuite/gdb.threads/gdb-barrier.c Tue Feb 19 09:49:56 2008 -0800
@@ -0,0 +1,70 @@
+/* gdb-barrier.c --- a portable implementation of barriers. */
+
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <pthread.h>
+
+/* The header file has more comments and explanation. */
+#include "gdb-barrier.h"
+
+static void
+check (int result, char *what)
+{
+ if (result)
+ {
+ fprintf (stderr, "error: %s: %s\n", what, strerror (result));
+ exit (1);
+ }
+}
+
+
+void
+gdb_barrier_init (struct gdb_barrier *b, int n)
+{
+ memset (b, 0, sizeof (*b));
+ check (pthread_mutex_init (&b->m, NULL),
+ "initializing barrier mutex");
+ check (pthread_cond_init (&b->c, NULL),
+ "initializing barrier condition");
+ b->full_count = n;
+ b->pending = n;
+}
+
+
+int
+gdb_barrier_wait (struct gdb_barrier *b)
+{
+ int result;
+
+ check (pthread_mutex_lock (&b->m),
+ "locking barrier mutex");
+ {
+ int my_cycle = b->cycle;
+
+ b->pending--;
+ if (b->pending > 0)
+ {
+ result = 0;
+
+ /* Condition variables are allowed to let threads wake up
+ spuriously, so we need to verify that the barrier has moved
+ on to the next cycle, and wait again if it hasn't. */
+ while (b->cycle == my_cycle)
+ check (pthread_cond_wait (&b->c, &b->m),
+ "waiting on barrier condition");
+ }
+ else
+ {
+ result = 1;
+ b->cycle++;
+ b->pending = b->full_count;
+ check (pthread_cond_broadcast (&b->c),
+ "broadcasting barrier condition");
+ }
+ }
+ check (pthread_mutex_unlock (&b->m),
+ "releasing barrier mutex");
+
+ return result;
+}
diff -r b72cf86f9dad gdb/testsuite/gdb.threads/gdb-barrier.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/gdb/testsuite/gdb.threads/gdb-barrier.h Tue Feb 19 09:50:38 2008 -0800
@@ -0,0 +1,34 @@
+/* gdb-barrier.h --- barriers built on POSIX-only thread primitives. */
+
+#ifndef GDB_BARRIER_H
+#define GDB_BARRIER_H
+
+#include <pthread.h>
+
+/* POSIX does provide barriers, but they're optional, and not all
+ systems implement them. This is a simple implementation of
+ barriers in terms of the non-optional POSIX threads operations. */
+
+struct gdb_barrier
+{
+ pthread_mutex_t m; /* Mutex protecting this barrier. */
+ pthread_cond_t c; /* Queue of threads waiting at barrier. */
+
+ int full_count; /* Number of threads this barrier stops
+ per cycle.*/
+ int pending; /* Number of threads left to wait for. */
+ int cycle; /* Current cycle number. */
+};
+
+
+/* Initialize *B with a count of N (used by gdb_barrier_wait; see
+ below). Exit on failure. */
+extern void gdb_barrier_init (struct gdb_barrier *b, int n);
+
+/* Wait at barrier *B. Once N threads are waiting on the barrier,
+ those N threads are allowed to continue. This function returns
+ true in exactly one of the N threads allowed to continue, and false
+ in the other N-1 threads. Exit on failure. */
+extern int gdb_barrier_wait (struct gdb_barrier *b);
+
+#endif /* GDB_BARRIER_H */
diff -r b72cf86f9dad gdb/testsuite/gdb.threads/sigthread.c
--- a/gdb/testsuite/gdb.threads/sigthread.c Tue Feb 19 09:36:34 2008 -0800
+++ b/gdb/testsuite/gdb.threads/sigthread.c Tue Feb 19 09:37:13 2008 -0800
@@ -15,12 +15,14 @@
#include <pthread.h>
#include <signal.h>
+#include "gdb-barrier.h"
+
/* Loop long enough for GDB to send a few signals of its own, but
don't hang around eating CPU forever if something goes wrong during
testing. */
#define NSIGS 10000000
-pthread_barrier_t barrier;
+struct gdb_barrier barrier;
void
handler (int sig)
@@ -36,7 +38,7 @@ child_two (void *arg)
{
int i;
- pthread_barrier_wait (&barrier);
+ gdb_barrier_wait (&barrier);
for (i = 0; i < NSIGS; i++)
pthread_kill (child_thread, SIGUSR1);
@@ -47,7 +49,7 @@ thread_function (void *arg)
{
int i;
- pthread_barrier_wait (&barrier);
+ gdb_barrier_wait (&barrier);
for (i = 0; i < NSIGS; i++)
pthread_kill (child_thread_two, SIGUSR2);
@@ -60,13 +62,13 @@ int main()
signal (SIGUSR1, handler);
signal (SIGUSR2, handler);
- pthread_barrier_init (&barrier, NULL, 3);
+ gdb_barrier_init (&barrier, 3);
main_thread = pthread_self ();
pthread_create (&child_thread, NULL, thread_function, NULL);
pthread_create (&child_thread_two, NULL, child_two, NULL);
- pthread_barrier_wait (&barrier);
+ gdb_barrier_wait (&barrier);
for (i = 0; i < NSIGS; i++)
pthread_kill (child_thread_two, SIGUSR1);
diff -r b72cf86f9dad gdb/testsuite/gdb.threads/sigthread.exp
--- a/gdb/testsuite/gdb.threads/sigthread.exp Tue Feb 19 09:36:34 2008 -0800
+++ b/gdb/testsuite/gdb.threads/sigthread.exp Tue Feb 19 09:37:13 2008 -0800
@@ -18,7 +18,9 @@ set srcfile ${testfile}.c
set srcfile ${testfile}.c
set binfile ${objdir}/${subdir}/${testfile}
-if {[gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" "${binfile}" \
+if {[gdb_compile_pthreads \
+ "${srcdir}/${subdir}/${srcfile} ${srcdir}/${subdir}/gdb-barrier.c" \
+ "${binfile}" \
executable { debug }] != "" } {
return -1
}
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