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Date:      Fri, 19 Nov 1999 10:18:22 -0800
From:      "Scott Hess" <scott@avantgo.com>
To:        "Daniel Eischen" <eischen@vigrid.com>, <freebsd-hackers@FreeBSD.ORG>
Subject:   Re: EINTR problems with multithreaded programs.
Message-ID:  <03e501bf32ba$76d83550$1e80000a@avantgo.com>
References:  <199911191814.NAA02164@pcnet1.pcnet.com>
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[-- Attachment #1 --]
Daniel Eischen <eischen@vigrid.com> wrote:
>Scott Hess mailto:scott@avantgo.com wrote:
> > When using -pthread on FreeBSD3.3 to build a multithreaded program, I
find
> > that signals are delivered to all threads (see attached program).
> > Specifically, if multiple threads are in blocking read calls, and a
signal
> > is handled, they will all receive -1 from the read and EINTR in errno.
>
> If you don't want all threads to see the signal(s), then you
> have to block the signal(s) in each thread.

I've checked further, and found that FreeBSD correctly handles blocking
signals on a per-thread basis.  _But_, all threads still get EINTR when a
signal happens while they're in a blocking read.

I've attached the updated program that shows the correct delivery of the
signals, with system calls still being interrupted.  [Sorry about the
attachment, but that seems the safest way to go about getting the file
delivered in usable fashion.]

Thanks,
scott


[-- Attachment #2 --]
#include <pthread.h>
#include <errno.h>
#include <sys/types.h>
#include <signal.h>

static void signal_handler( int sig)
{
    printf( "%p Got signal %d\n", pthread_self(), sig);
}

static void *reader( void *arg)
{
    char buf[ 1024];
    int cc;
    int ii=(int)arg;
    int fd=dup( 0);
    sigset_t set;
    
    sigemptyset( &set);
    if( (ii%3)==0 || (ii%3)==1) {
        sigaddset( &set, SIGUSR1);
    }
    if( (ii%3)==0 || (ii%3)==2) {
        sigaddset( &set, SIGUSR2);
    }
    pthread_sigmask( SIG_BLOCK, &set, NULL);

    {
        struct sigaction sa_usr1={ signal_handler, 0, SA_RESTART};
        struct sigaction sa_usr2={ signal_handler, 0, SA_RESTART};
        sigaction( SIGUSR1, &sa_usr1, NULL);
        sigaction( SIGUSR2, &sa_usr2, NULL);
    }

    printf( "%p/%d waiting for data\n", pthread_self(), ii);
    while(1) {
        cc=read( fd, buf, sizeof( buf));
        if( cc>=0) {
            printf( "%p got %d bytes\n", pthread_self(), cc);
        } else {
            printf( "%p saw errno==%d/%s\n", pthread_self(), errno, strerror( errno));
        }
    }
    return NULL;
}

void main( void)
{
    int ii, cc=9;
    pthread_t child;
    
#if 0
    signal( SIGUSR1, signal_handler);
#else
    {
        struct sigaction sa_usr1={ signal_handler, 0, SA_RESTART};
        struct sigaction sa_usr2={ signal_handler, 0, SA_RESTART};
        sigaction( SIGUSR1, &sa_usr1, NULL);
        sigaction( SIGUSR2, &sa_usr2, NULL);
    }
#endif

    for( ii=0; ii<cc; ii++) {
        if( pthread_create( &child, NULL, reader, (void *)ii)) {
            perror( "spawning thread");
            exit( 1);
        }
    }
    while( 1) {
        sleep( 2);
        kill( getpid(), SIGUSR1);
        sleep( 2);
        kill( getpid(), SIGUSR2);
    }
    exit( 0);
}

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