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Date: Fri, 31 Oct 2003 13:14:17 +0800
From: "zhouxin" <zhoux AT harbournetworks DOT com>
To: "cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Subject: select() take 100% CPU with cygwin1.5.5-1 in WinXP/Win2000
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Cygwin implementation of select() take 100% CPU under multi-thread environment sometimes.
I have wrote a short test program(see below test_select.c) that reproduces the bug:
#uname -a 
CYGWIN_NT-5.1 zipxing 1.5.5(0.94/3/2) 2003-09-20 16:31 i686 unknown
#gcc -o tsel test_select.c
#./tsel 5 (5 threads, no problem)
^C
#./tsel 17(17 threads, no problem)
^C
#./tsel 18(18 threads, tsel take 100% cpu!!! It seems that 18 is a critical value.) 

and I compile and execute test_select.c in solaris9,all ok...
Is this a bug of Cygwin implementation of select()?
help,thanks!

test_select.c
___________________________________________________________________
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/select.h>
#include <sys/socket.h>

//Select timeout...
int timeout = 30;
//Thread count...
int tcount  = 20;

//Thread function...
void *
tp(void *ptr) {
    int sockfd = 0;
    int tid;
    tid = (int)ptr;
        
    if((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0){
        fprintf(stderr, "cannot open socket for udp packet!\n");
        exit(1);
    }
        
    while(1){
        struct timeval    tv;
        fd_set            fds;
        
        FD_ZERO(&fds);
        FD_SET(sockfd, &fds);
        
        tv.tv_sec  =  timeout;
        tv.tv_usec = 0;
        printf("select the socket_fd : %d, thread_id is : %d\n", 
                sockfd, tid);
        select(sockfd + 1, &fds, NULL, NULL, &tv);
    }
}

//Initial thread pool...
void 
thread_pool_init() {
    int i;
    pthread_t thrid;
        
    for(i=0; i<tcount; i++) 
        pthread_create(&thrid, NULL, tp, (void *)i);
}

int 
main(int argc, char *argv[])
{  
    if(argc>1) 
        tcount = atoi(argv[1]);
    
    thread_pool_init();

    while(1){
        sleep(10000);
    }
}
_____________________________________________________________________________________





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