signal註冊訊號陷阱

使用signal註冊訊號，有可能不會使阻塞通訊端被訊號打斷，請看如下代碼：

/** * Try to reproduce this issue: *      Set an alarm before connect() of blocking socket, connect() won't be *      interrupted when this alarm is fired. * gcc -o signal signal.c */#include <signal.h>#include <unistd.h>#include <stdio.h>#include <sys/types.h>#include <sys/socket.h>#include <netinet/in.h>#include <arpa/inet.h>#include <netinet/in.h>#include <errno.h>#include <stdarg.h>#include <string.h>#include <stdlib.h>voidsig_handler(int sig){    printf("in signal handler\n");}die(const char *fmt, ...){    char buf[1024] = {0};    va_list va;    va_start(va, fmt);    vsnprintf(buf, sizeof(buf), fmt, va);    va_end(va);    fprintf(stderr, "%s\n", buf);    exit(1); /* stdlib.h */}intmain(int argc, char **argv){#ifdef USE_SIGACTION    struct sigaction sa;    memset(&sa, 0, sizeof(sa));    sa.sa_handler = sig_handler;    if(sigaction(SIGALRM, &sa, NULL) < 0)        die("sigaction failed");#else    if(SIG_ERR == signal(SIGALRM, sig_handler)) {        die("signal failed\n");    }#endif    int sock = socket(AF_INET, SOCK_STREAM, 0);    struct sockaddr_in to;    memset(&to, 0, sizeof(to));    to.sin_family = AF_INET;    if(!inet_aton("192.168.1.254", &to.sin_addr)) {        die("convert failed");    }    to.sin_port = htons(22322);    alarm(2);    if(connect(sock, (struct sockaddr*)&to, sizeof(to)) < 0 &&            errno == EINTR) {        close(sock);        die("connect() is interrupted");    }    return 0;}

不定義宏USE_SIGACTION，使用signal註冊訊號，connect()永遠不會被打斷。
但是使用sigaction註冊訊號，能夠使connect函數被訊號打斷：

$gcc -o signal signal.c -DUSE_SIGACTION$./signal in signal handlerconnect() is interrupted

我的環境：

$gcc --versiongcc (GCC) 4.4.2 20091027 (Red Hat 4.4.2-7)$uname -r2.6.31.5-127.fc12.i686.PAE

結論：盡量使用sigaction註冊訊號。

網上這方面的資料很少，參考SO一個文章：

http://stackoverflow.com/questions/3582226/recv-is-not-interrupted-by-a-signal-in-multithreaded-environment