HP OpenVMS Systems Documentation

Attempts to lock the specified mutex.

Syntax

tis_mutex_trylock(
mutex );

Argument	Data Type	Access
mutex	opaque pthread_mutex_t	read

int
tis_mutex_trylock (
pthread_mutex_t *mutex);

Arguments

mutex

Address of the mutex (passed by reference) to be locked.

Description

This routine attempts to lock the specified mutex mutex. When this routine is called, an attempt is made immediately to lock the mutex. If the mutex is successfully locked, zero (0) is returned.

If the specified mutex is already locked when this routine is called, the caller does not wait for the mutex to become available. [EBUSY] is returned, and the thread does not wait to acquire the lock.

Associated Routines

tis_mutex_destroy()
tis_mutex_init()
tis_mutex_lock()
tis_mutex_unlock()

Unlocks the specified mutex.

Syntax

tis_mutex_unlock(
mutex );

Argument	Data Type	Access
mutex	opaque pthread_mutex_t	read

int
tis_mutex_unlock (
pthread_mutex_t *mutex);

Arguments

mutex

Address of the mutex (passed by reference) to be unlocked.

Description

This routine unlocks the specified mutex mutex.

For more information about actions taken when threads are present, refer to the pthread_mutex_unlock() description.

Associated Routines

tis_mutex_destroy()
tis_mutex_init()
tis_mutex_lock()
tis_mutex_trylock()

Calls a one-time initialization routine that can be executed by only one thread, once.

Syntax

tis_once(
once _control,
init _routine );

Argument	Data Type	Access
once_control	opaque pthread_once_t	modify
init_routine	procedure	read

int
tis_once (
pthread_once_t *once_control,
void (*init_routine) (void));

Arguments

once_control

Address of a record (control block) that defines the one-time initialization code. Any one-time initialization routine in static storage specified by once_control must have its own unique pthread_once_t record.

init_routine

Address of a procedure that performs the initialization. This routine is called only once, regardless of the number of times it and its associated once_control are passed to tis_once() .

Description

The first call to this routine by a process with a given once_control calls the init_routine with no arguments. Thereafter, subsequent calls to tis_once() with the same once_control do not call the init_routine. On return from tis_once() , it is guaranteed that the initialization routine has completed.

For example, a mutex or a thread-specific data key must be created exactly once. In a threaded environment, calling tis_once() ensures that the initialization is serialized across multiple threads.

Note If you specify an init_routine that directly or indirectly results in a recursive call to tis_once() and that specifies the same init_block argument, the recursive call results in a deadlock.

The PTHREAD_ONCE_INIT macro, defined in the pthread.h header file, must be used to initialize a once_control record. Thus, your program must declare a once_control record as follows:

pthread_once_t once_control = PTHREAD_ONCE_INIT;

Note that it is often easier to simply lock a statically initialized mutex, check a control flag, and perform necessary initialization (in-line) rather than using tis_once() . For example, you can code an "init" routine that begins with the following basic logic:

init() { static pthread_mutex_t mutex = PTHREAD_MUTEX_INIT; static int flag = FALSE; tis_mutex_lock(&mutex); if(!flag) { flag = TRUE; /* initialize code */ } tis_mutex_unlock(&mutex); }

Acquires a read-write lock for read access.

Syntax

tis_read_lock(
lock );

Argument	Data Type	Access
lock	opaque tis_rwlock_t	write

int
tis_read_lock (
tis_rwlock_t *lock);

Arguments

lock

Address of the read-write lock.

Description

This routine acquires a read-write lock for read access. This routine waits for any existing lock holder for write access to relinquish its lock before granting the lock for read access. This routine returns when the lock is acquired. If the lock is already held simply for read access, the lock is granted.

For each call to tis_read_lock() that successfully acquires the lock for read access, a corresponding call to tis_read_unlock() must be issued.

Associated Routines

tis_read_trylock()
tis_read_unlock()
tis_rwlock_destroy()
tis_rwlock_init()
tis_write_lock()
tis_write_trylock()
tis_write_unlock()

Attempts to acquire a read-write lock for read access. Does not wait if the lock cannot be immediately granted.

Syntax

tis_read_trylock(
lock );

Argument	Data Type	Access
lock	opaque tis_rwlock_t	write

int
tis_read_trylock (
tis_rwlock_t *lock);

Arguments

lock

Address of the read-write lock to be acquired.

Description

This routine attempts to acquire a read-write lock for read access. If the lock cannot be granted, the routine returns without waiting.

When a thread calls this routine, an attempt is made to immediately acquire the lock for read access. If the lock is acquired, zero (0) is returned. If a holder of the lock for write access exists, [EBUSY] is returned.

If the lock cannot be acquired for read access immediately, the calling program does not wait for the lock to be released.

Associated Routines

tis_read_lock()
tis_read_unlock()
tis_rwlock_destroy()
tis_rwlock_init()
tis_write_lock()
tis_write_trylock()
tis_write_unlock()

Unlocks a read-write lock that was acquired for read access.

Syntax

tis_read_unlock(
lock );

Argument	Data Type	Access
lock	opaque tis_rwlock_t	write

int
tis_read_unlock (
tis_rwlock_t *lock);

Arguments

lock

Address of the read-write lock to be unlocked.

Description

This routine unlocks a read-write lock that was acquired for read access. If there are no other holders of the lock for read access and another thread is waiting to acquire the lock for write access, that lock acquisition is granted.

Associated Routines

tis_read_lock()
tis_read_trylock()
tis_rwlock_destroy()
tis_rwlock_init()
tis_write_lock()
tis_write_trylock()
tis_write_unlock()

Destroys the specified read-write lock object.

Syntax

tis_rwlock_destroy(
lock );

Argument	Data Type	Access
lock	opaque tis_rwlock_t	write

int
tis_rwlock_destroy (
tis_rwlock_t *lock);

Arguments

lock

Address of the read-write lock object to be destroyed.

Description

This routine destroys the specified read-write lock object. Prior to calling this routine, ensure that there are no locks granted to the specified read-write lock and that there are no threads waiting for pending lock acquisitions on the specified read-write lock.

This routine should be called only after all reader threads (and perhaps one writer thread) have finished using the specified read-write lock.

Associated Routines

tis_read_lock()
tis_read_trylock()
tis_read_unlock()
tis_rwlock_init()
tis_write_lock()
tis_write_trylock()
tis_write_unlock()

Initializes a read-write lock object.

Syntax

tis_rwlock_init(
lock );

Argument	Data Type	Access
lock	opaque tis_rwlock_t	write

int
tis_rwlock_init (
tis_rwlock_t *lock);

Arguments

lock

Address of a read-write lock object.

Description

This routine initializes a read-write lock object. The routine initializes the tis_rwlock_t structure that holds the object's lock states.

To destroy a read-write lock object, call the tis_rwlock_destroy() routine.

Note The tis read-write lock has no relationship to the Single UNIX Specification, Version 2 (SUSV2, or UNIX98) read-write lock routines (such as pthread_rwlock_init() ). The tis_rwlock_t type, in particular, cannot be used with the pthread read-write lock functions, nor can a pthread_rwlock_t type be used with the tis read-write lock functions.

Associated Routines

tis_read_lock()
tis_read_trylock()
tis_read_unlock()
tis_rwlock_destroy()
tis_write_lock()
tis_write_trylock()
tis_write_unlock()

Returns the identifier of the calling thread.

Syntax

tis_self(
void);

pthread_t
tis_self (void);

Arguments

None

Description

This routine allows a thread to obtain its own thread identifier.

This value becomes meaningless when the thread is destroyed.

Note that the initial thread in a process can "change identity" when thread system initialization completes---that is, when the multithreading run-time environment is loaded.

Associated Routines

pthread_create()

Changes the calling thread's cancelability state.

Syntax

tis_setcancelstate(
state ,
oldstate );

Argument	Data Type	Access
state	integer	read
oldstate	integer	write

int
tis_setcancelstate (
int state,
int *oldstate );

Arguments

state

State of general cancelability to set for the calling thread. Valid state values are as follows:

PTHREAD_CANCEL_ENABLE
PTHREAD_CANCEL_DISABLE

oldstate

Receives the value of the calling thread's previous cancelability state.

Description

This routine sets the calling thread's cancelability state to the value specified in the state argument and returns the calling thread's previous cancelability state in the location referenced by the oldstate argument.

When a thread's cancelability state is set to PTHREAD_CANCEL_DISABLE , a cancelation request cannot be delivered to the thread, even if a cancelable routine is called or asynchronous cancelability is enabled.

When a thread is created, its default cancelability state is PTHREAD_CANCEL_ENABLE . When this routine is called prior to loading threads, the cancelability state propagates to the initial thread in the executing program.

Possible Problems When Disabling Cancelability

The most important use of a cancelation request is to ensure that indefinite wait operations are terminated. For example, a thread waiting on some network connection, which might take days to respond (or might never respond), should be made cancelable.

When a thread's cancelability state is disabled, no routine called within that thread is cancelable. As a result, the user is unable to cancel the operation. When disabling cancelability, be sure that no long waits can occur or that it is necessary for other reasons to defer cancelation requests around that particular region of code.

If an error condition occurs, this routine returns an integer value indicating the type of error. Possible return values are as follows:

Associated Routines

tis_testcancel()