Subject: lib/20256: sem_wait in libpthread fails in single-threaded mode
To: None <>
From: Anthony Mallet <>
List: netbsd-bugs
Date: 02/08/2003 21:40:21
>Number:         20256
>Category:       lib
>Synopsis:       sem_wait in libpthread fails in single-threaded mode
>Confidential:   no
>Severity:       serious
>Priority:       low
>Responsible:    lib-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Feb 08 12:41:00 PST 2003
>Originator:     Anthony Mallet
>Release:        NetBSD 1.6N
System: NetBSD ficus 1.6N NetBSD 1.6N (FICUS) #0: Sun Feb 2 17:53:57 CET 2003 troot@ficus:/home/build/netbsd-obj-current/sys/arch/i386/compile/FICUS i386
Architecture: i386
Machine: i386
sem_wait from libpthread triggers an assert in single-threaded mode:

assertion "next != 0" failed: file
"/home/src/netbsd-current/lib/libpthread/pthread_run.c", line 118,
function "pthread__next"

This PR follows up on the discussion that took place in PR#20001.

Compile and run the following:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>
#include <pthread.h>
#include <semaphore.h>
#include <sys/types.h>
#include <sys/time.h>

sem_t		sem;

void		timer_func(int);

main(int argc, char *argv[])
   pthread_t		thread;
   struct itimerval	tv;
   int			status;

   status = sem_init(&sem, 0, 0);
   if (status) { perror("sem_init"); return 2; }

   /* prepare for receiving SIGALRM */
   signal(SIGALRM, timer_func);

   /* setup a timer that starts after 1s */
   tv.it_interval.tv_usec = 0;
   tv.it_interval.tv_sec = 0;
   tv.it_value.tv_usec = 0;
   tv.it_value.tv_sec = 1;

   status = setitimer(ITIMER_REAL, &tv, NULL);
   if (status) { perror("setitimer"); return 2; }

   /* block on the semaphore */
   printf("before sem_wait\n");
   printf("after sem_wait\n");

   return 0;

/* SIGALRM handler */
timer_func(int dummy)
   printf("before sem_post\n");
   printf("after sem_post\n");