Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755906AbYJ3W2S (ORCPT ); Thu, 30 Oct 2008 18:28:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753101AbYJ3W2G (ORCPT ); Thu, 30 Oct 2008 18:28:06 -0400 Received: from host4.CastelHQ.com ([66.152.210.4]:11510 "EHLO casmail.hq.castel.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752826AbYJ3W2E convert rfc822-to-8bit (ORCPT ); Thu, 30 Oct 2008 18:28:04 -0400 X-Greylist: delayed 934 seconds by postgrey-1.27 at vger.kernel.org; Thu, 30 Oct 2008 18:28:04 EDT MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT x-cr-puzzleid: {9C36A52D-6439-4841-922F-2AF570B4B2C4} X-MimeOLE: Produced By Microsoft Exchange V6.5 x-cr-hashedpuzzle: CD67 Cw1D DCCx DKs/ Done EK38 EVuv EnqU FGyd GoHk G2Eb JEvr J1tO J4KR KgCN Kr08;1;bABpAG4AdQB4AC0AawBlAHIAbgBlAGwAQAB2AGcAZQByAC4AawBlAHIAbgBlAGwALgBvAHIAZwA=;Sosha1_v1;7;{9C36A52D-6439-4841-922F-2AF570B4B2C4};agByAGUAbgB0AG8AbgBAAGMAYQBzAHQAZQBsAC4AYwBvAG0A;Thu, 30 Oct 2008 22:12:14 GMT;cwBpAGcAcQB1AGUAdQBlACgAKQAgAGwAbwBzAGkAbgBnACAAcwBpAGcAbgBhAGwAcwA= Content-class: urn:content-classes:message Subject: sigqueue() losing signals Date: Thu, 30 Oct 2008 18:12:14 -0400 Message-ID: <10058ACA10EE3444BBBC5FCF84825F63417127@casmail.hq.castel.com> X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: sigqueue() losing signals Thread-Index: Ack63JBKYgFDwt9kS9OdY3I9inn/tA== From: "James Renton" To: Cc: "Joe Maldonado" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4360 Lines: 159 I needed to kick off a bunch of background threads and receive notification if one failed due to fatal error. I was hoping waitpid() would work; but found out quickly that although each thread has a pid_t; threads and processes were not interchangeable. Without a timed pthread_join() over multiple threads (like WIN32 WaitForMultipleObjects), I formulated a seemingly dead simple implementation using signals. I hacked out a quick prototype to ensure I could get the signals to work as desired. When I ran the prototype, I experienced behavior looking very bug-like; but I wanted to post it here in case I am misunderstanding unix signals and just doing something silly. I am requesting for comments or [hopefully clever] suggestions... Code follows:


#include 
#include 
#include 
#include 
#include 
#include 
#include 

siginfo_t signal_info;
pthread_t thread_main;
pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;

_syscall0(pid_t,gettid)

void *fThrd( void *context )
{
    union sigval val;
    val.sival_int = gettid();
    printf( "{%d} TID started OK\n", gettid() );
    sleep( 5 );
    printf( "{%d} TID exiting...\n", gettid() );

    //xxpthread_mutex_lock( &mtx );
    while( 0!=sigqueue( getpid(), SIGCHLD, val ) )
    {
        printf( "ERR=[%d]\n", errno );
        if( EAGAIN!=errno )
            break;
        //xxusleep( 10000 );
    }
    //xxusleep( 10000 );
    //xxpthread_mutex_unlock( &mtx );
};

void fSigChld( int signal, siginfo_t *pInfo, void* context )
{
    printf( "{%d} SIGCHLD called...\n", gettid() );
    if( getpid()!=gettid() || signal!=SIGCHLD )
        return;
    memcpy( &signal_info, pInfo, sizeof(siginfo_t) );
    printf( "{%d} SIGCHLD executed OK\n", gettid() );
}

int main( int argc, char* argv[] )
{
    pthread_t hT = 0;
    struct sigaction act;
    int rc = -1,i;
    const pid_t ppid = getppid();
  
    thread_main = pthread_self();

    memset( &signal_info, 0x00, sizeof(signal_info) );
    printf( "{%d} Parent PID={%d}\n", gettid(), ppid ); 

    for( i=0;i<5;i++ )
         rc = pthread_create( &hT, NULL, &fThrd, NULL );

    memset( &act, 0x00, sizeof(act) );   
    act.sa_flags = SA_SIGINFO;
    act.sa_sigaction = &fSigChld;
    rc = sigaction( SIGCHLD, &act, NULL );

    for( ;; )
    {
       printf( "{%d} PID sleeping...\n", gettid() );
       sleep(11);
       if( 0!=signal_info.si_pid )
           printf( "  SIGNAL SRC={%d} OK\n",
signal_info.si_value.sival_int);
       memset( &signal_info, 0x00, sizeof(signal_info) );     
    };

    printf( "{%d} PID exiting...\n", gettid() );
    return rc;    
};

When I execute it in 2.6.9-42.EL, I get the following output: {10321} Parent PID={10235} {10321} PID sleeping... {10322} TID started OK {10323} TID started OK {10324} TID started OK {10325} TID started OK {10326} TID started OK {10322} TID exiting... {10323} TID exiting... {10324} TID exiting... {10325} TID exiting... {10326} TID exiting... {10321} SIGCHLD called... {10321} SIGCHLD executed OK SIGNAL SRC={10322} OK {10321} PID sleeping... {10321} PID sleeping... As you can see, 4/5 of the signals are lost. When I uncomment the other lines above, (in fThrd); the output looks better: {10355} Parent PID={10235} {10355} PID sleeping... {10356} TID started OK {10357} TID started OK {10358} TID started OK {10359} TID started OK {10360} TID started OK {10356} TID exiting... {10357} TID exiting... {10358} TID exiting... {10359} TID exiting... {10360} TID exiting... {10355} SIGCHLD called... {10355} SIGCHLD executed OK SIGNAL SRC={10356} OK {10355} PID sleeping... {10355} SIGCHLD called... {10355} SIGCHLD executed OK SIGNAL SRC={10357} OK {10355} PID sleeping... {10355} SIGCHLD called... {10355} SIGCHLD executed OK SIGNAL SRC={10358} OK {10355} PID sleeping... {10355} SIGCHLD called... {10355} SIGCHLD executed OK SIGNAL SRC={10359} OK {10355} PID sleeping... {10355} SIGCHLD called... {10355} SIGCHLD executed OK SIGNAL SRC={10360} OK {10355} PID sleeping... {10355} PID sleeping... James Beverly, MA USA -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/