Possible race condition for pthread_join

This test is from openposixtestsuite, test conformance/interfaces/sigwait/6-1.test pthread_join seems to be causing a problem some of the time. Adding a print statement just before pthread_join caused the test to pass when the output is directed to the display, but not when the test is run with output redirected.

/*
* Copyright (c) 2005, Bull S.A..  All rights reserved.
* Created by: Sebastien Decugis

* This program is free software; you can redistribute it and/or modify it
* under the terms of version 2 of the GNU General Public License as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it would be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write the Free Software Foundation, Inc., 59
* Temple Place - Suite 330, Boston MA 02111-1307, USA.


* This sample test aims to check the following assertion:
*
* If several threads are blocked in a call to sigwait, 
* only one is unblocked when the signal becomes pending. 


* The steps are:
* -> mask SIGUSR1
* -> create several threads which sigwait for SIGUSR1
* -> raise SIGUSR1
* -> Check than only 1 thread has been awaken.

* The test fails if less or more than 1 thread returns from sigwait when the 
* signal is raised.

*/


/* We are testing conformance to IEEE Std 1003.1, 2003 Edition */
#define _POSIX_C_SOURCE 200112L

/******************************************************************************/
/*************************** standard includes ********************************/
/******************************************************************************/
#include <pthread.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <signal.h>
#include <errno.h>

/******************************************************************************/
/***************************   Test framework   *******************************/
/******************************************************************************/
#include "testfrmw.h"
#include "testfrmw.c" 
/* This header is responsible for defining the following macros:
 * UNRESOLVED(ret, descr);  
 *    where descr is a description of the error and ret is an int 
 *   (error code for example)
 * FAILED(descr);
 *    where descr is a short text saying why the test has failed.
 * PASSED();
 *    No parameter.
 * 
 * Both three macros shall terminate the calling process.
 * The testcase shall not terminate in any other maneer.
 * 
 * The other file defines the functions
 * void output_init()
 * void output(char * string, ...)
 * 
 * Those may be used to output information.
 */

/******************************************************************************/
/**************************** Configuration ***********************************/
/******************************************************************************/
#ifndef VERBOSE
#define VERBOSE 1
#endif

#define NTHREADS 5

/******************************************************************************/
/***************************    Test case   ***********************************/
/******************************************************************************/

int n_awaken = 0;
sigset_t setusr;

/* Thread function */
void * threaded( void * arg )
{
	int ret;
	int sig;

	/* The signal is already masked, because inherited from the parent */

	/* wait for the signal */
	ret = sigwait( &setusr, &sig );

	if ( ret != 0 )
	{
		UNRESOLVED( ret, "failed to wait for signal in thread" );
	}

	n_awaken++;

	/* quit */
	return NULL;
}

/* The main test function. */
int main( int argc, char * argv[] )
{
	int ret, i;
	pthread_t ch[ NTHREADS ];

	/* Initialize output */
	output_init();

	/* Set the signal mask */
	ret = sigemptyset( &setusr );

	if ( ret != 0 )
	{
		UNRESOLVED( ret, "Failed to empty signal set" );
	}

	ret = sigaddset( &setusr, SIGUSR1 );

	if ( ret != 0 )
	{
		UNRESOLVED( ret, "failed to add SIGUSR1 to signal set" );
	}

	ret = pthread_sigmask( SIG_BLOCK, &setusr, NULL );

	if ( ret != 0 )
	{
		UNRESOLVED( ret, "Failed to block SIGUSR1" );
	}

	/* Create the children */

	for ( i = 0; i < NTHREADS; i++ )
	{
		ret = pthread_create( &ch[ i ], NULL, threaded, NULL );

		if ( ret != 0 )
		{
			UNRESOLVED( ret, "Failed to create a thread" );
		}
	}

	/* raise the signal */
	ret = kill( getpid(), SIGUSR1 );

	if ( ret != 0 )
	{
		UNRESOLVED( ret, "Failed to raise the signal" );
	}

	sleep( 1 );

	if ( n_awaken != 1 )
	{
		output( "%d threads were awaken\n", n_awaken );
		FAILED( "Unexpected number of threads awaken" );
	}

	/* Wake other threads */
	for ( ; n_awaken < NTHREADS ; sched_yield() )
	{
		ret = kill( getpid(), SIGUSR1 );

		if ( ret != 0 )
		{
			UNRESOLVED( ret, "Failed to raise the signal" );
		}
	}

	/* Wait for child thread termination */
	for ( i = 0; i < NTHREADS; i++ )
	{
		ret = pthread_join( ch[ i ], NULL );

		if ( ret != 0 )
		{
			UNRESOLVED( ret, "Failed to join the thread" );
		}
	}

	/* Test passed */
#if VERBOSE > 0

	output( "Test passed\n" );

#endif

	PASSED;
}