Question

C++里怎么调用wait

Answer 1

　　创建子进程后，父进程具有监听子进程的运行状态的能力，用到的函数为：

　　#include <sys/wait.h>
   pid_t wait(int *status);
   pid_t waitpid(pid_t pid, int *status, int options);

　　以上函数用于等待子进程子进程旦凯轿的状态变化回调并且获取状态变化信息。所能获取到的状态变化包括：子进程运行结束、子进程被信号量暂停、子进程被信号量恢复运行。

　　父进程执行了wait函数后，如果子进程已模肆经发生了状态变化，则wait函数立即就会有返回结果；否则wait函数会一直阻塞直至子进程状态发生变化。

　　通常意义上，如果子进程已经发生了状态变化，但还未被父进程或其它系统回调执行wait，孙型则把此时的子进程称为是可等待的(waitable)。

　　子进程运行结束后，父进行执行wait函数可以推动系统释放与子进程相关的资源；否则子进程将会被维持在僵尸进程的状态下一直存在。　　

Answer 2

创建子进程后，父进程具有监听子进程的运行状态的能力，用到中高搜的函数为：

　　#include <sys/wait.h>
   pid_t wait(int *status);
   pid_t waitpid(pid_t pid, int *status, int options);

　　以上函数用于等待子进程子进程的状态变化回调并卖历且获取状态变化信息。所能获取到的状态变化包括：子进程运行结束、子进程被信号量暂停、子进程被信号量恢复运行。

　　父进程执行了wait函数后，如果子进程已经发生了状态变化，则wait函数立即就会有返回结果；否则wait函数会一直阻塞直至子进程状态发生变化。

　　通常意义上，如果子进程已经发生了状态变化，但还未被父进程或其它系统回调执行wait，则把此时的子进程称为是可等待的(waitable)。

　　子进念悔程运行结束后，父进行执行wait函数可以推动系统释放与子进程相关的资源；否则子进程将会被维持在僵尸进程的状态下一直存在。　　

Answer 3

多线程液旦里的同步的wait API函坦搏数;
MSDN 里的说明：
To enter an alertable wait state, use the WaitForSingleObjectEx function. To wait for multiple objects, use the WaitForMultipleObjects.

Syntax
CopyDWORD WINAPI WaitForSingleObject(
__in HANDLE hHandle,
__in DWORD dwMilliseconds
);
Parameters
hHandle [in]
A handle to the object. For a list of the object types whose handles can be specified, see the following Remarks section.

If this handle is closed while the wait is still pending, the function's behavior is undefined.

The handle must have the SYNCHRONIZE access right. For more information, see Standard Access Rights.

dwMilliseconds [in]
The time-out interval, in milliseconds. If a nonzero value is specified, the function waits until the object is signaled or the interval elapses. If dwMilliseconds is zero, the function does not enter a wait state if the object is not signaled; it always returns immediately. If dwMilliseconds is INFINITE, the function will return only when the object is signaled.

========================================================
The WaitForSingleObject function can wait for the following objects:

•Change notification
•Console input
•Event
•Memory resource notification
•Mutex
•Process
•Semaphore
•Thread
•Waitable timer

MS的例子：

#include <windows.h>
#include <stdio.h>

#define THREADCOUNT 2

HANDLE ghMutex;

DWORD WINAPI WriteToDatabase( LPVOID );

int main( void )
{
HANDLE aThread[THREADCOUNT];
DWORD ThreadID;
int i;

// Create a mutex with no initial owner

ghMutex = CreateMutex(
NULL, // default security attributes
FALSE, // initially not owned
NULL); //闹信扰 unnamed mutex

if (ghMutex == NULL)
{
printf("CreateMutex error: %d\n", GetLastError());
return 1;
}

// Create worker threads

for( i=0; i < THREADCOUNT; i++ )
{
aThread[i] = CreateThread(
NULL, // default security attributes
0, // default stack size
(LPTHREAD_START_ROUTINE) WriteToDatabase,
NULL, // no thread function arguments
0, // default creation flags
&ThreadID); // receive thread identifier

if( aThread[i] == NULL )
{
printf("CreateThread error: %d\n", GetLastError());
return 1;
}
}

// Wait for all threads to terminate

WaitForMultipleObjects(THREADCOUNT, aThread, TRUE, INFINITE);

// Close thread and mutex handles

for( i=0; i < THREADCOUNT; i++ )
CloseHandle(aThread[i]);

CloseHandle(ghMutex);

return 0;
}

DWORD WINAPI WriteToDatabase( LPVOID lpParam )
{
// lpParam not used in this example
UNREFERENCED_PARAMETER(lpParam);

DWORD dwCount=0, dwWaitResult;

// Request ownership of mutex.

while( dwCount < 20 )
{
dwWaitResult = WaitForSingleObject(
ghMutex, // handle to mutex
INFINITE); // no time-out interval

switch (dwWaitResult)
{
// The thread got ownership of the mutex
case WAIT_OBJECT_0:
__try {
// TODO: Write to the database
printf("Thread %d writing to database...\n",
GetCurrentThreadId());
dwCount++;
}

__finally {
// Release ownership of the mutex object
if (! ReleaseMutex(ghMutex))
{
// Handle error.
}
}
break;

// The thread got ownership of an abandoned mutex
// The database is in an indeterminate state
case WAIT_ABANDONED:
return FALSE;
}
}
return TRUE;
}

Answer 4

wait() ;不是c++的函数。是windows的函数所以伍运#include<windows.h>搭镇就可以知橘粗了。

Answer 5

把windows库加进去，#include<windows.h>