Bug 30781
| Summary: | msgrcv call blocks other pthread's jobs | ||
|---|---|---|---|
| Product: | Base System | Reporter: | Choi, Dong-won <dwchoe> |
| Component: | kern | Assignee: | freebsd-bugs (Nobody) <bugs> |
| Status: | Closed FIXED | ||
| Severity: | Affects Only Me | ||
| Priority: | Normal | ||
| Version: | Unspecified | ||
| Hardware: | Any | ||
| OS: | Any | ||
On Mon, Sep 24, 2001 at 01:58:54AM -0700, dwchoe@naver.com wrote: > > >Number: 30781 > >Category: kern > >Synopsis: msgrcv call blocks other pthread's jobs > >Originator: Choi, Dong-won > >Release: FreeBSD 4.2-20010108-STABLE > >Organization: > Naver.COM > >Environment: > FreeBSD 4.2-20010108-STABLE #0: Thu Jan 11 09:23:26 KST 2001 /usr/src/sys/compile/MYKERNEL i386 > >Description: > A program using msgrcv call and pthread do not run as expected. > One thread calls msgrcv and wait until some messages are arrived. > Other thread does its given jobs. > And some other threads can call msgsnd to send messages. > All threads need to run concurruntly. > It's just ok under Linux or SunOS. In FreeBSD, all threads live within one process. This means that if one thread should make a blocking system call, the whole process blocks until the call returns. The way around this is to make your system calls not block. For syscalls dealing with file descriptors, the fd's need to be set into non-blocking mode. Other syscalls have their own ways of specifying non-blocking operation. For msgrcv(3), it is the msgflg parameter - read the msgrcv(3) manual page and set the IPC_NOWAIT flag. Then have your main thread call msgrcv(3) in non-blocking mode and if it returns nothing, sleep for a while before the next call. G'luck, Peter -- What would this sentence be like if it weren't self-referential? > For msgrcv(3), it is the msgflg parameter - read the msgrcv(3) manual page > and set the IPC_NOWAIT flag. Then have your main thread call msgrcv(3) > in non-blocking mode and if it returns nothing, sleep for a while before > the next call. That's not really "message waiting" architecture than. Sending process should trigger the event and listening process should awake on it. Just like with sockets. Looks like that's currently impossible in FreeBSD with msgXXX functions without interrupting the other threads. Anyway shouldn't it be some generic uniform way to wakeup processes/threads on events working the same way on msgXXX, FDs, process start/end, other events? Yuri. This PR is duplicated with kern/21783: http://www.FreeBSD.org/cgi/query-pr.cgi?pr=kern/21783 -- Maxim Konovalov, MAcomnet, Internet-Intranet Dept., system engineer phone: +7 (095) 796-9079, mailto: maxim@macomnet.ru State Changed From-To: open->closed Duplicate of kern/30781. |
A program using msgrcv call and pthread do not run as expected. One thread calls msgrcv and wait until some messages are arrived. Other thread does its given jobs. And some other threads can call msgsnd to send messages. All threads need to run concurruntly. It's just ok under Linux or SunOS. How-To-Repeat: ----- test.c ------------- #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <pthread.h> #include <sys/ipc.h> #include <sys/msg.h> void *Thread(void *vArg); struct stmq { long id; }; struct stmq mqSt; main(int argc, char *argv[]) { int i; int mqid; pthread_t thSelect; pthread_attr_t taAttr; if( (mqid = msgget(0x20, 0666 | IPC_CREAT)) == -1 ) exit(0); pthread_attr_init (&taAttr); pthread_attr_setscope (&taAttr, PTHREAD_SCOPE_SYSTEM); pthread_attr_setdetachstate(&taAttr, PTHREAD_CREATE_DETACHED); for(i=0; i<2; i++) { if(pthread_create(&thSelect, &taAttr, Thread, NULL) != 0) exit(0); } while(1) { printf("Main...\n"); fflush(stdout); msgrcv(mqid, &mqSt, sizeof(mqSt)-sizeof(long), 0, 0); } } void *Thread(void *vArg) { printf("Thread...\n"); fflush(stdout); while(1); } ------- End of test.c Under FreeBSD $ gcc test.c -pthread $ a.out Main... Under Linux or SunOS $ a.out Main... Thread... Thread...