Hello!
For the record, scm_spawn_thread sometimes return #f, instead of a valid
thread, when called from start_signal_delivery_thread, itself called
from the pthread key destructor.
For this reason, I added an assertion check in commit 0f4f2d9a, which
gets hit systematically on that platform, for instance when running
standalone/test-scm-spawn-thread.
The backtrace looks like this:
--8<---------------cut here---------------start------------->8---
(gdb) thread apply all bt
Thread 3 (Thread 801a041c0 (LWP 100363)):
#0 0x00000008012903cc in __error () from /lib/libthr.so.3
#1 0x000000080128e501 in pthread_cond_signal () from /lib/libthr.so.3
#2 0x00000008007196e1 in scm_pthread_cond_timedwait (cond=0x640e28,
mutex=0x640ca8, wt=0x7fffffffd980) at ../../libguile/threads.c:2024
#3 0x00000008007198cd in block_self (queue=0x855e20, sleep_object=Variable
"sleep_object" is not available.
) at ../../libguile/threads.c:454
#4 0x0000000800719d65 in scm_join_thread_timed (thread=0x855e50,
timeout=0x13c963492, timeoutval=Variable "timeoutval" is not available.
) at ../../libguile/threads.c:1295
#5 0x0000000000400c33 in inner_main (data=Variable "data" is not available.
) at ../../../test-suite/standalone/test-scm-spawn-thread.c:55
#6 0x00000008006a067a in c_body (d=0x7fffffffdbe0) at
../../libguile/continuations.c:518
#7 0x0000000800727803 in vm_regular_engine (vm=0x6add50, program=0x6b00c0,
argv=0x1, nargs=8680160) at vm-i-system.c:1007
#8 0x000000080071fbc6 in scm_c_vm_run (vm=0x6add50, program=0x785930,
argv=0x7fffffffdb40, nargs=4) at ../../libguile/vm.c:567
#9 0x00000008006a7ce3 in scm_call_4 (proc=0x785930, arg1=Variable "arg1" is
not available.
) at ../../libguile/eval.c:506
#10 0x00000008006a09f9 in scm_i_with_continuation_barrier (body=0x8006a0670
<c_body>, body_data=0x7fffffffdbe0, handler=0x8006a08b0 <c_handler>,
handler_data=0x7fffffffdbe0,
pre_unwind_handler=0x8006a0710 <pre_unwind_handler>,
pre_unwind_handler_data=0x6adc80) at ../../libguile/continuations.c:455
#11 0x00000008006a0ad5 in scm_c_with_continuation_barrier (func=Variable "func"
is not available.
) at ../../libguile/continuations.c:552
#12 0x000000080071b470 in with_guile_and_parent (base=0x7fffffffdc40,
data=Variable "data" is not available.
) at ../../libguile/threads.c:913
#13 0x000000080114ed75 in GC_call_with_stack_base () from
/nix/store/rc9flhds6pwpb9wvi55v2f9h7mkzsj0x-boehm-gc-7.2pre20110122/lib/libgc.so.1
#14 0x000000080071abf1 in scm_i_with_guile_and_parent (func=Variable "func" is
not available.
) at ../../libguile/threads.c:959
#15 0x0000000000400b80 in main (argc=Variable "argc" is not available.
) at ../../../test-suite/standalone/test-scm-spawn-thread.c:68
Thread 2 (Thread 801a0ae40 (LWP 100280)):
#0 0x00000008016250dc in thr_kill () from /lib/libc.so.7
#1 0x00000008016c1dcb in abort () from /lib/libc.so.7
#2 0x00000008016ab1a5 in __assert () from /lib/libc.so.7
#3 0x000000080071ab2d in scm_spawn_thread (body=Variable "body" is not
available.
) at ../../libguile/threads.c:1175
#4 0x00000008006f7ab1 in start_signal_delivery_thread () at
../../libguile/scmsigs.c:211
#5 0x000000080128d9c8 in pthread_once () from /lib/libthr.so.3
#6 0x000000080071b1b0 in do_thread_exit (v=Variable "v" is not available.
) at ../../libguile/threads.c:666
#7 0x00000008006a067a in c_body (d=0x7fffffbfedc0) at
../../libguile/continuations.c:518
#8 0x0000000800727803 in vm_regular_engine (vm=0x855e00, program=0x8570c0,
argv=0x1, nargs=9272864) at vm-i-system.c:1007
#9 0x000000080071fbc6 in scm_c_vm_run (vm=0x855e00, program=0x785930,
argv=0x7fffffbfed20, nargs=4) at ../../libguile/vm.c:567
#10 0x00000008006a7ce3 in scm_call_4 (proc=0x785930, arg1=Variable "arg1" is
not available.
) at ../../libguile/eval.c:506
#11 0x00000008006a09f9 in scm_i_with_continuation_barrier (body=0x8006a0670
<c_body>, body_data=0x7fffffbfedc0, handler=0x8006a08b0 <c_handler>,
handler_data=0x7fffffbfedc0,
pre_unwind_handler=0x8006a0710 <pre_unwind_handler>,
pre_unwind_handler_data=0x6adc80) at ../../libguile/continuations.c:455
#12 0x00000008006a0ad5 in scm_c_with_continuation_barrier (func=Variable "func"
is not available.
) at ../../libguile/continuations.c:552
#13 0x0000000801153bc8 in GC_call_with_gc_active () from
/nix/store/rc9flhds6pwpb9wvi55v2f9h7mkzsj0x-boehm-gc-7.2pre20110122/lib/libgc.so.1
#14 0x000000080071b411 in with_guile_and_parent (base=0x7fffffbfee60,
data=Variable "data" is not available.
) at ../../libguile/threads.c:236
#15 0x000000080114ed75 in GC_call_with_stack_base () from
/nix/store/rc9flhds6pwpb9wvi55v2f9h7mkzsj0x-boehm-gc-7.2pre20110122/lib/libgc.so.1
#16 0x000000080071abf1 in scm_i_with_guile_and_parent (func=Variable "func" is
not available.
) at ../../libguile/threads.c:959
#17 0x000000080114ed75 in GC_call_with_stack_base () from
/nix/store/rc9flhds6pwpb9wvi55v2f9h7mkzsj0x-boehm-gc-7.2pre20110122/lib/libgc.so.1
#18 0x000000080071af2e in on_thread_exit (v=Variable "v" is not available.
) at ../../libguile/threads.c:748
#19 0x000000080128985b in pthread_key_delete () from /lib/libthr.so.3
#20 0x000000080128f5f3 in pthread_exit () from /lib/libthr.so.3
#21 0x00000008012864f9 in pthread_getprio () from /lib/libthr.so.3
#22 0x0000000000000000 in ?? ()
Cannot access memory at address 0x7fffffbff000
Thread 1 (Thread 801a35c80 (LWP 100403)):
#0 0x00000008016c4fcc in write () from /lib/libc.so.7
#1 0x00000008016c4a60 in memcpy () from /lib/libc.so.7
#2 0x00000008016c49ab in memcpy () from /lib/libc.so.7
#3 0x00000008016c359d in f_prealloc () from /lib/libc.so.7
#4 0x00000008016c2d5c in fwrite () from /lib/libc.so.7
#5 0x00000008016b5f3b in open () from /lib/libc.so.7
#6 0x00000008016b74e9 in open () from /lib/libc.so.7
#7 0x00000008016b98da in vfprintf () from /lib/libc.so.7
#8 0x00000008016a794a in printf () from /lib/libc.so.7
#9 0x000000080071b040 in really_spawn (d=0x7fffffbfeaa0) at
../../libguile/threads.c:1100
---Type <return> to continue, or q <return> to quit---
#10 0x00000008006a067a in c_body (d=0x7fffff9fde70) at
../../libguile/continuations.c:518
#11 0x0000000800727803 in vm_regular_engine (vm=0x801fc0, program=0x8d80c0,
argv=0x1, nargs=9272448) at vm-i-system.c:1007
#12 0x000000080071fbc6 in scm_c_vm_run (vm=0x801fc0, program=0x785930,
argv=0x7fffff9fddd0, nargs=4) at ../../libguile/vm.c:567
#13 0x00000008006a7ce3 in scm_call_4 (proc=0x785930, arg1=Variable "arg1" is
not available.
) at ../../libguile/eval.c:506
#14 0x00000008006a09f9 in scm_i_with_continuation_barrier (body=0x8006a0670
<c_body>, body_data=0x7fffff9fde70, handler=0x8006a08b0 <c_handler>,
handler_data=0x7fffff9fde70,
pre_unwind_handler=0x8006a0710 <pre_unwind_handler>,
pre_unwind_handler_data=0x6adc80) at ../../libguile/continuations.c:455
#15 0x00000008006a0ad5 in scm_c_with_continuation_barrier (func=Variable "func"
is not available.
) at ../../libguile/continuations.c:552
#16 0x000000080071b470 in with_guile_and_parent (base=0x7fffff9fded0,
data=Variable "data" is not available.
) at ../../libguile/threads.c:913
#17 0x000000080114ed75 in GC_call_with_stack_base () from
/nix/store/rc9flhds6pwpb9wvi55v2f9h7mkzsj0x-boehm-gc-7.2pre20110122/lib/libgc.so.1
#18 0x000000080071abf1 in scm_i_with_guile_and_parent (func=Variable "func" is
not available.
) at ../../libguile/threads.c:959
#19 0x000000080071ac74 in spawn_thread (d=Variable "d" is not available.
) at ../../libguile/threads.c:1133
#20 0x000000080115337c in GC_inner_start_routine () from
/nix/store/rc9flhds6pwpb9wvi55v2f9h7mkzsj0x-boehm-gc-7.2pre20110122/lib/libgc.so.1
#21 0x000000080114ed75 in GC_call_with_stack_base () from
/nix/store/rc9flhds6pwpb9wvi55v2f9h7mkzsj0x-boehm-gc-7.2pre20110122/lib/libgc.so.1
#22 0x00000008012864f1 in pthread_getprio () from /lib/libthr.so.3
#23 0x0000000000000000 in ?? ()
Cannot access memory at address 0x7fffff9fe000
#0 0x00000008016250dc in thr_kill () from /lib/libc.so.7
--8<---------------cut here---------------end--------------->8---
Adding printfs shows that the thread calling scm_spawn_thread leaves
cond_wait before the signal thread has signaled the condition (in
really_spawn).
A similar program succeeds, suggesting that it’s not a bug/limitation of
libpthread:
--8<---------------cut here---------------start------------->8---
#include <pthread.h>
#include <assert.h>
#include <stdlib.h>
#include <stdio.h>
#define GC_THREADS 1
#include <gc/gc.h>
struct sync
{
pthread_cond_t cond;
pthread_mutex_t mutex;
};
static void *
hello (void *arg)
{
int err;
struct sync *s = (struct sync *) arg;
printf ("hello from %p\n", pthread_self ());
GC_MALLOC (123);
err = pthread_mutex_lock (&s->mutex);
assert (err == 0);
err = pthread_cond_signal (&s->cond);
assert (err == 0);
err = pthread_mutex_unlock (&s->mutex);
assert (err == 0);
}
static void
on_thread_exit ()
{
int err;
pthread_t child;
struct sync s;
pthread_mutex_init (&s.mutex, NULL);
pthread_cond_init (&s.cond, NULL);
pthread_mutex_lock (&s.mutex);
err = pthread_create (&child, NULL, hello, &s);
assert (err == 0);
err = pthread_cond_wait (&s.cond, &s.mutex);
assert (err == 0);
err = pthread_mutex_unlock (&s.mutex);
assert (err == 0);
printf ("child %p seen from %p\n", child, pthread_self ());
}
static void *
entry (void *unused)
{
pthread_key_t k;
pthread_key_create (&k, on_thread_exit);
pthread_setspecific (k, (void *) 123);
return NULL;
}
int
main ()
{
int err;
pthread_t child;
void *ret;
GC_INIT ();
err = pthread_create (&child, NULL, entry, NULL);
assert (err == 0);
err = pthread_join (child, &ret);
assert (err == 0);
return 0;
}
--8<---------------cut here---------------end--------------->8---
To be continued...
Ludo’.
