Programming with POSIX® Threads

72 status = pthread_cond_signal (&request->done);

73 if (status != 0)

74 err_abort (status, "Signal server condition");

75 status = pthread_mutex_unlock (&tty_server.mutex);

76 if (status != 0)

77 err_abort (status, "Unlock server mutex");

78 } else

79 free (request);

80 if (operation == REQ_QUIT)

81 break;

82 }

83 return NULL;

84 }

Part 3 shows the function that is called to initiate a request to the tty server thread. The caller specifies the desired operation (REQ_QUIT, REQ_READ, or REQ_ WRITE), whether the operation is synchronous or not (sync), an optional prompt string (prompt) for REQ_READ operations, and the pointer to a string (input for REQ_WRITE, or a buffer to return the result of an REQ_READ operation).

16-40 If a tty server thread is not already running, start one. A temporary thread attributes object (detached_attr) is created, and the detachstate attribute is set to PTHREAD_CREATE_DETACHED. Thread attributes will be explained later in Section 5.2.3. In this case, we are just saying that we will not need to use the thread identifier after creation.

45-76 Allocate and initialize a server request (request_t) packet. If the request is synchronous, initialize the condition variable (done) in the request packet — otherwise the condition variable isn't used. The new request is linked onto the request queue.

81-83 Wake the server thread to handle the queued request.

88-105 If the request is synchronous, wait for the server to set done_flag and signal the done condition variable. If the operation is REQ_READ, copy the result string into the output buffer. Finally, destroy the condition variable, and free the request packet.

■ server.c part 3 tty_server_request

1 /*

2 * Request an operation

3 */

4 void tty_server_request (

5 int operation,

6 int sync,

7 const char *prompt,

8 char *string)

9 {

10 request_t *request;

11 int status;

12

13 status = pthread_mutex_lock (&tty_server.mutex);

14 if (status != 0)

15 err_abort (status, "Lock server mutex");

16 if (!tty_server.running) {

17 pthread_t thread;

18 pthread_attr_t detached_attr;

19

20 status = pthread_attr_init (&detached_attr);

21 if (status != 0)

22 err_abort (status, "Init attributes object");

23 status = pthread_attr_setdetachstate (

24 &detached_attr, PTHREAD_CREATE_DETACHED);

25 if (status != 0)

26 err_abort (status, "Set detach state");

27 tty_server.running = 1;

28 status = pthread_create (&thread, &detached_attr,

29 tty_server_routine, NULL);

30 if (status != 0)

31 err_abort (status, "Create server");

32

33 /*

34 * Ignore an error in destroying the attributes object.

35 * It's unlikely to fail, there's nothing useful we can

36 * do about it, and it's not worth aborting the program

37 * over it.

38 */

39 pthread_attr_destroy (&detached_attr);

40 }

41

42 /*

43 * Create and initialize a request structure.

44 */

45 request = (request_t*)malloc (sizeof (request_t));

46 if (request == NULL)

47 errno_abort ("Allocate request");

48 request->next = NULL;

49 request->operation = operation;

50 request->synchronous = sync;

51 if (sync) {

52 request->done_flag = 0;

53 status = pthread_cond_init (&request->done, NULL);

54 if (status != 0)

55 err_abort (status, "Init request condition");

56 }

57 if (prompt != NULL)