APUE中sigpending代碼解釋不了解

jiangf

AUPE第二版的10.13節(jié)中講到 sigpending 函數(shù),對(duì)下面的這段代碼不了解

#include "apue.h" static void sig_quit(int); int main(void) { &nbsp;&nbsp;&nbsp;&nbsp;sigset_t    newmask, oldmask, pendmask; &nbsp;&nbsp;&nbsp;&nbsp;if (signal(SIGQUIT, sig_quit) == SIG_ERR) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;err_sys("can't catch SIGQUIT"); &nbsp;&nbsp;&nbsp;&nbsp;/* &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;* Block SIGQUIT and save current signal mask. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;*/ &nbsp;&nbsp;&nbsp;&nbsp;sigemptyset(&newmask); &nbsp;&nbsp;&nbsp;&nbsp;sigaddset(&newmask, SIGQUIT); &nbsp;&nbsp;&nbsp;&nbsp;if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;err_sys("SIG_BLOCK error"); &nbsp;&nbsp;&nbsp;&nbsp;sleep(5);   /* SIGQUIT here will remain pending */ &nbsp;&nbsp;&nbsp;&nbsp;if (sigpending(&pendmask) < 0) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;err_sys("sigpending error"); &nbsp;&nbsp;&nbsp;&nbsp;if (sigismember(&pendmask, SIGQUIT)) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf("\nSIGQUIT pending\n"); &nbsp;&nbsp;&nbsp;&nbsp;/* &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;* Reset signal mask which unblocks SIGQUIT. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;*/ &nbsp;&nbsp;&nbsp;&nbsp;if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;err_sys("SIG_SETMASK error"); &nbsp;&nbsp;&nbsp;&nbsp;printf("SIGQUIT unblocked\n"); &nbsp;&nbsp;&nbsp;&nbsp;sleep(5);   /* SIGQUIT here will terminate with core file */ &nbsp;&nbsp;&nbsp;&nbsp;exit(0); } static void sig_quit(int signo) { &nbsp;&nbsp;&nbsp;&nbsp;printf("caught SIGQUIT\n"); &nbsp;&nbsp;&nbsp;&nbsp;if (signal(SIGQUIT, SIG_DFL) == SIG_ERR) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;err_sys("can't reset SIGQUIT"); }

代碼輸出:
SIGQUIT pending          after return from sleep
caught SIGQUIT           in signal handler
SIGQUIT unblocked        after return from sigprocmask


在 if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0)這句代碼中已經(jīng)講SIGQUIT信號(hào)阻塞了,在未解除阻塞之前這么還會(huì)捕
獲到SIGQUIT這個(gè)信號(hào)呢.

jiangf

補(bǔ)充一下,AUPE中對(duì)這個(gè)情況的解釋是SIGQUIT在進(jìn)程睡眠期間產(chǎn)生,這個(gè)信號(hào)現(xiàn)在是未決的并且是非阻塞的,所以它會(huì)在sigprocmask 函數(shù)返回之前遞送給該進(jìn)程.
If we generate the quit signal during this sleep period, the signal is now pending and unblocked, so it is delivered before sigprocmask returns.

在sleep之前進(jìn)程該信號(hào)都已經(jīng)阻塞了呀,怎么還說(shuō)是非阻塞

bobozhang

你沒(méi)有搞懂吧，是這句if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0) unblock后才收到的sigquit，因?yàn)閟igprocmask是一個(gè)系統(tǒng)調(diào)用，在從它返回用戶(hù)空間時(shí)內(nèi)核會(huì)去檢查信號(hào)的，這時(shí)，sigquit已經(jīng)可以處理了，于是就馬上處理后才回到用戶(hù)空間執(zhí)行那句printf("SIGQUIT unblocked\n");當(dāng)然就是你看到的輸入順序了

[ 本帖最后由 bobozhang 于 2009-5-6 10:38 編輯 ]

wwdwwd

是這樣的：在信號(hào)被阻塞期間發(fā)送給進(jìn)程的信號(hào)會(huì)被推遲發(fā)送，直到進(jìn)程解除對(duì)某信號(hào)的阻塞，這時(shí)候信號(hào)才會(huì)到來(lái)
請(qǐng)看apue p269頁(yè)