Linux thread (2): Termination of Thread

 

If any thread in the process calls exit, _ exit, _ exit, the whole process is terminated. This is not the thread termination, but the process, which terminates all threads in the process.

 

1. Thread termination method:

A single thread can exit in three ways:

• The return value is the exit code of the thread.
• Canceled by other threads in the same process.
• Call pthread_exit.

 

2. pthread_exit function:

• Prototype: void pthread_exit (void * rval_ptr );
• Header file: <pthread. h>
• Parameter: rval_ptr is a non-type pointer pointing to the return value of the thread to store the variable.

 

3. pthread_join function:

• Prototype: int pthread_join (pthread_t thread, void ** rval_ptr );
• Header file: <pthread. h>
• Returned value: 0 is returned if the request is successful. Otherwise, the error number is returned.
• Parameters:
• Thread: thread ID.
• Rval_ptr: pointer to the returned value (the returned value is also a pointer ).
• Note:
• The Calling thread will be blocked until the specified Thread calls pthread_exit and is returned or canceled from the startup routine.
• If the thread returns from its startup routine, rval_ptr contains the return code.
• If the thread is canceled, the memory unit specified by rval_ptr is set to pthread_canceled.
• If you do not care about the returned value, set rval_ptr to null.

 

4. instance:

Main. C code:

# Include <pthread. h>
# Include <stdio. h>


/** // * Print process and thread IDs */
Void printids (const char * s)
...{
Pid_t PID, ppid;
Pthread_t tid;

PID = getpid ();
Ppid = getppid ();
Tid = pthread_self ();

Printf ("% 16 s PID % 5u ppid % 5u TID % 16u (0x % x )",
S, (unsigned INT) PID, (unsigned INT) ppid,
(Unsigned INT) tid, (unsigned INT) tid );
}

/** // * Thread process */
Void * thread_func (void * Arg );
...{
Printids ("New thread :");
Return (void *) 108;
}

/** // * Main func */
Int main ()
...{
Int err;
Void * tret;/** // * thread return value */
Pthread_t ntid;

Err = pthread_create (& ntid, null, thread_func, null );
If (Err! = 0)
Perror ("can't create thread ");

Err = pthread_join (ntid, & tret );
If (Err! = 0)
Perror ("can't join thread ");

Printids ("main thread :");
Printf ("thread exit code: % d", (INT) tret );
Sleep (1 );

Return 0;
}

This code is adapted from the previous instance. The execution process is as follows:

• First, create a new thread. After printing IDs, the thread returns 108.
• Then, use pthread_join to obtain the return value of the thread, which is stored in the Tret.
• The main thread prints IDs.
• The main thread prints the Tret, that is, the return value of the new thread.

 

5. pthread_cancel function:

• Prototype: int pthread_cancel (pthread_t tid );
• Header file: <pthread. h>
• Returned value: 0 is returned if the request is successful. Otherwise, the error number is returned.
• Note:
• It is equivalent to calling pthread_exit with the parameter pthread_canceled.
• Cancel does not wait for the thread to terminate. It only initiates a request.
• The thread can choose to ignore or control the cancellation method.