Frank_Fang 2009-07-09 10:07 发表评论
]]>Frank_Fang 2009-07-09 10:06 发表评论
]]>假设有共享的资源sum,与之相关联的mutex 是lock_s.假设每个U程对sum的操作很单的,与sum的状态无?比如只是sum++.那么只用mutex_?E序员只要确保每个线E操作前,取得lock,然后sum++,再unlock卛_.每个U程的代码将像这样add()
{
pthread_mutex_lock(lock_s);
sum++;
pthread_mutex_unlock(lock_s);
}
如果操作比较复杂,假设U程t0,t1,t2的操作是sum++,而线Et3则是在sum到达100的时?打印Z条信?q对sum清零.q种情况?如果只用mutex, 则t3需要一个@?每个循环里先取得lock_s,然后查sum的状?如果sum>=100,则打印ƈ清零,然后unlock.如果sum<100,则unlock,qsleep()本线E合适的一D|?
q个时?t0,t1,t2的代码不?t3的代码如?br />
print()
{
while (1)
{
pthread_mutex_lock(lock_s);
if(sum<100)
{
printf(“sum reach 100!”);
pthread_mutex_unlock(lock_s);
}
else
{
pthread_mutex_unlock(lock_s);
my_thread_sleep(100);
return OK;
}
}
}
q种办法有两个问?br />
1) sum在大多数情况下不会到?00,那么对t3的代码来?大多数情况下,走的是else分支,只是lock和unlock,然后sleep().q浪费了CPU处理旉.
2) Z节省CPU处理旉,t3会在探测到sum没到?00的时候sleep()一D|?q样却又带来另外一个问?亦即t3响应速度下降.可能在sum到达200的时?t3才会醒过?
3) q样,E序员在讄sleep()旉的时候陷入两隑֢?讄得太短了节省不了资源,太长了又降低响应速度.真是隑֊?
q个时?condition variable内裤外穿,从天而降,拯救了焦头烂额的?
你首先定义一个condition variable.
pthread_cond_t cond_sum_ready=PTHREAD_COND_INITIALIZER;
t0,t1,t2的代码只要后面加两行,像这?br />
add()
{
pthread_mutex_lock(lock_s);
sum++;
pthread_mutex_unlock(lock_s);
if(sum>=100)
pthread_cond_signal(&cond_sum_ready);
}
而t3的代码则?br />
print
{
pthread_mutex_lock(lock_s);
while(sum<100)
pthread_cond_wait(&cond_sum_ready, &lock_s);
printf(“sum is over 100!”);
sum=0;
pthread_mutex_unlock(lock_s);
return OK;
}
注意两点:
1) 在thread_cond_wait()之前,必须先lock相关联的mutex, 因ؓ假如目标条g未满?pthread_cond_wait()实际上会unlock该mutex, 然后block,在目标条件满_再重新lock该mutex, 然后q回.
2) Z么是while(sum<100),而不是if(sum<100) ?q是因ؓ在pthread_cond_signal()和pthread_cond_wait()q回之间,有时间差,假设在这个时间差?q有另外一个线Et4又把sum减少?00以下?那么t3在pthread_cond_wait()q回之后,昄应该再检查一遍sum的大?q就是用while的用?/p>
boost lib
http://www.stlchina.org/twiki/bin/view.pl/Main/BoostThread#safag7ZYn7rqw
文章出处QDIY部落(http://www.diybl.com/course/3_program/c++/cppxl/20090508/166837.html)
Frank_Fang 2009-07-05 01:07 发表评论
]]>基本操作
#include <semaphore.h>int sem_init(sem_t *sem, int pshared, unsigned int value);
int sem_wait(sem_t *sem); /* P(sem), wait(sem) */
int sem_post(sem_t *sem); /* V(sem), signal(sem) */int sem_getvalue(sem_t *sem, int *sval);int sem_trywait(sem_t *sem);int sem_destroy(sem_t *sem); /* undo sem_init() *//* named semaphores - these are less useful here */sem_t *sem_open( 
);int sem_close(sem_t *sem);int sem_unlink(const char *name);互斥?/strong>
基本操作
#include <pthread.h>int pthread_mutex_init(pthread_mutex_t *mutex, pthread_mutexattr_t *attr);pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;int pthread_mutex_lock(pthread_mutex_t *mutex);int pthread_mutex_unlock(pthread_mutex_t *mutex);int pthread_mutex_trylock(pthread_mutex_t *mutex);int pthread_mutex_destroy(pthread_mutex_t *mutex); 条g变量
一U信h?/p>
基本操作
#include <pthread.h>int pthread_cond_init(pthread_cond_t *cond, pthread_condattr_t *attr);pthread_cond_t cond = PTHREAD_COND_INITIALIZER;int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);int pthread_cond_signal(pthread_cond_t *cond);int pthread_cond_timedwait( );int pthread_cond_broadcast(pthread_cond_t *cond);int pthread_cond_destroy(pthread_cond_t *cond); 互斥量A保护条g变量B
//{待?/span>pthread_mutex_lock(&A);while(){//查条件是否满?/span>
pthread_cond_wait(&B, &A);
} /* wait会隐式解锁A */ /* wait后A会被隐式锁住A */pthread_mutex_unlock(&A);//通知?/span>pthread_mutex_lock(&A);pthread_cond_signal(&B);pthread_mutex_unlock(&A);Frank_Fang 2009-07-05 01:02 发表评论
]]>#include<sys/types.h>
#include<sys/wait.h>
定义函数 pid_t waitpid(pid_t pid,int * status,int options);
函数说明
waitpid()会暂时停止目前进E的执行,直到有信h到或子进E?br /> l束。如果在调用 wait()时子q程已经l束,?wait()会立?br /> q回子进E结束状态倹{?子进E的l束状态g由参?status q回,
而子q程的进E识别码也会一赯回。如果不在意l束状态??br /> 参数 status 可以设成 NULL。参?pid 为欲{待的子q程识别?
其他数值意义如?
pid<-1 {待q程l识别码?pid l对值的M子进E?br /> pid=-1 {待M子进E?相当?wait()?
pid=0 {待q程l识别码与目前进E相同的M子进E?
pid>0 {待M子进E识别码?pid 的子q程?br /> 参数 option 可以?0 或下面的 OR l合:
WNOHANG 如果没有M已经l束的子q程则马上返? 不予以等待?br /> WUNTRACED 如果子进E进入暂停执行情况则马上q回,但结束状态不予以理会?br /> 子进E的l束状态返回后存于 status,底下有几个宏可判别结束情?
WIFEXITED(status)如果子进E正常结束则为非 0 倹{?br /> WEXITSTATUS(status)取得子进E?exit()q回的结束代?一般会先用 WIFEXITED 来判断是否正常结束才能用此宏?br /> WIFSIGNALED(status)如果子进E是因ؓ信号而结束则此宏gؓ?br /> WTERMSIG(status) 取得子进E因信号而中止的信号代码,一般会先用 WIFSIGNALED 来判断后才用此宏?br /> WIFSTOPPED(status) 如果子进E处于暂停执行情况则此宏gؓ真。一般只有?WUNTRACED 时才会有此情c?br /> WSTOPSIG(status) 取得引发子进E暂停的信号代码,一般会先用 WIFSTOPPED 来判断后才用此宏?br /> 如果执行成功则返回子q程识别?PID) ,如果有错误发生则q回
q回?1。失败原因存?errno 中?br /> /******
* waitpid.c - Simple wait usage
*********/
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
int main( void )
{
pid_t childpid;
int status;
childpid = fork();
if ( -1 == childpid )
{
perror( "fork()" );
exit( EXIT_FAILURE );
}
else if ( 0 == childpid )
{
puts( "In child process" );
sleep( 3 );//让子q程睡眠3U，看看父进E的行ؓ
printf("\tchild pid = %d\n", getpid());
printf("\tchild ppid = %d\n", getppid());
exit(EXIT_SUCCESS);
}
else
{
waitpid( childpid, &status, 0 );
puts( "in parent" );
printf( "\tparent pid = %d\n", getpid() );
printf( "\tparent ppid = %d\n", getppid() );
printf( "\tchild process exited with status %d \n", status );
}
exit(EXIT_SUCCESS);
}
[root@localhost src]# gcc waitpid.c
[root@localhost src]# ./a.out
In child process
child pid = 4469
child ppid = 4468
in parent
parent pid = 4468
parent ppid = 4379
child process exited with status 0
[root@localhost src]#
如果上?#8220;waitpid( childpid, &status, 0 );”行注释掉Q程序执行效果如下：
[root@localhost src]# ./a.out
In child process
in parent
parent pid = 4481
parent ppid = 4379
child process exited with status 1331234400
[root@localhost src]# child pid = 4482
child ppid = 1
子进E还没有退出，父进E已l退Z?
Frank_Fang 2009-07-05 00:01 发表评论
]]>ACE
Frank_Fang 2009-06-02 13:16 发表评论
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