pthread退出釋放資源的問題！

nicle

請看我的線程代碼：

1. 
   
2. void * run(void * arg)
   
3. {
   
4.    char *buff = NULL;
   
5.    
   
6.    buff = malloc(SIZE);
   
7.    
   
8.    while(1){
   
9.        sleep(1);
   
10.    }   
    
11. 
    
12.    free(buff);
    
13. }
    

復制代碼

這個是我的子線程，運行起來后，我在主線程里調(diào)用pthread_cancel, 停掉子線程，其中的buff會被free嗎？

westgarden

原帖由 nicle 于 2006-4-18 17:41 發(fā)表
請看我的線程代碼：

1. 
   
2. void * run(void * arg)
   
3. {
   
4.    char *buff = NULL;
   
5.    
   
6.    buff = malloc(SIZE);
   
7.    
   
8.    while(1){
   
9.        sleep(1);
   
10.    }   
    
11. 
    
12.    free(buff);
    
13. }
    

復制代碼

這個是我的子線程，運行起來后，我在主線程里調(diào)用pthread_cancel, 停掉子線程，其中的buff會被free嗎？

不會。

Cancelability-Enable為PTHREAD_CANCEL_ENABLE（默認）、
Cancelability Type為PTHREAD_CANCEL_DEFERRED（默認）的線程
只能在取消點(Cancellation Points)上響應(yīng)取消請求。
因此你的子線程會在sleep()上退出。


即使Cancelability Type為PTHREAD_CANCEL_ASYNCHRONOUS也不會，
因為while(1)是死循環(huán)。

你最好在free(buff);后加個輸出信息的語句檢驗一下。

Cancellation Points
Cancellation points shall occur when a thread is executing the following functions:


accept()
aio_suspend()
clock_nanosleep()
close()
connect()
creat()
fcntl()2
fdatasync()
fsync()
getmsg()
getpmsg()
lockf()
mq_receive()
mq_send()
mq_timedreceive()


mq_timedsend()
msgrcv()
msgsnd()
msync()
nanosleep()
open()
pause()
poll()
pread()
pselect()
pthread_cond_timedwait()
pthread_cond_wait()
pthread_join()
pthread_testcancel()
putmsg()


putpmsg()
pwrite()
read()
readv()
recv()
recvfrom()
recvmsg()
select()
sem_timedwait()
sem_wait()
send()
sendmsg()
sendto()
sigpause()
sigsuspend()


sigtimedwait()
sigwait()
sigwaitinfo()
sleep()
system()
tcdrain()
usleep()
wait()
waitid()
waitpid()
write()
writev()

[ 本帖最后由 westgarden 于 2006-4-18 19:08 編輯 ]

rwen2012

stuying...

yeehya

在westgarden正確的前提下,那如何釋放這個buf呢?
在這個程序結(jié)構(gòu)中通過pthread_testcancel來設(shè)置Cancellation Point 是沒有意義的.
我覺得,還是讓線程自己主動的退出才是安全的做法.
可以通過全局變量來指引.

[ 本帖最后由 yeehya 于 2006-4-19 10:03 編輯 ]

nicle

代碼中的while(1)在我們的項目中是一個block方式的read,因為某些原因必須使用block方式，就會出現(xiàn)上面的情況！！ 線程的停止要靠pthread_cancel來實現(xiàn)；

westgarden

原帖由 yeehya 于 2006-4-19 10:00 發(fā)表
在westgarden正確的前提下,那如何釋放這個buf呢?
在這個程序結(jié)構(gòu)中通過pthread_testcancel來設(shè)置Cancellation Point 是沒有意義的.
我覺得,還是讓線程自己主動的退出才是安全的做法.
可以通過全局變量來指引.

NAME
pthread_cleanup_pop, pthread_cleanup_push - establish cancellation handlers
SYNOPSIS
[THR]  #include <pthread.h>

void pthread_cleanup_pop(int execute);
void pthread_cleanup_push(void (*routine)(void*), void *arg);


DESCRIPTION
The pthread_cleanup_pop() function shall remove the routine at the top of the calling thread's cancellation cleanup stack and optionally invoke it (if execute is non-zero).

The pthread_cleanup_push() function shall push the specified cancellation cleanup handler routine onto the calling thread's cancellation cleanup stack. The cancellation cleanup handler shall be popped from the cancellation cleanup stack and invoked with the argument arg when:

The thread exits (that is, calls pthread_exit()).

The thread acts upon a cancellation request.

The thread calls pthread_cleanup_pop() with a non-zero execute argument.

These functions may be implemented as macros. The application shall ensure that they appear as statements, and in pairs within the same lexical scope (that is, the pthread_cleanup_push() macro may be thought to expand to a token list whose first token is '{' with pthread_cleanup_pop() expanding to a token list whose last token is the corresponding '}' ).

The effect of calling longjmp() or siglongjmp() is undefined if there have been any calls to pthread_cleanup_push() or pthread_cleanup_pop() made without the matching call since the jump buffer was filled. The effect of calling longjmp() or siglongjmp() from inside a cancellation cleanup handler is also undefined unless the jump buffer was also filled in the cancellation cleanup handler.

The effect of the use of return, break, continue, and goto to prematurely leave a code block described by a pair of pthread_cleanup_push() and pthread_cleanup_pop() functions calls is undefined.

RETURN VALUE
The pthread_cleanup_push() and pthread_cleanup_pop() functions shall not return a value.

ERRORS
No errors are defined.

These functions shall not return an error code of [EINTR].