HP OpenVMS Systems Documentation

Obtains the unique identifier for the specified thread.

Syntax

pthread_getsequence_np(
thread );

Argument	Data Type	Access
thread	opaque pthread_t	read

unsigned long
pthread_getsequence_np (
pthread_t thread);

Arguments

thread

Thread whose sequence number is to be obtained.

Description

This routine obtains and returns the thread sequence number for the thread identified by the thread object specified in the thread argument.

The thread sequence number provides a unique identifier for each existing thread. A thread's thread sequence number is never reused while the thread exists, but can be reused after the thread terminates. The debugger interfaces use this sequence number to identify each thread in commands and in display output.

The result of calling this routine is undefined if the thread argument does not specify a valid thread object.

Associated Routines

pthread_create()
pthread_self()

Obtains the thread-specific data associated with the specified key.

Syntax

pthread_getspecific(
key );

Argument	Data Type	Access
key	opaque pthread_key_t	read

void
*pthread_getspecific (
pthread_key_t key);

Arguments

key

The context key identifies the thread-specific data to be obtained.

Description

This routine obtains the thread-specific data associated with the specified key for the current thread. Obtain this key by calling the pthread_key_create() routine. This routine returns the value currently bound to the specified key on behalf of the calling thread.

This routine may be called from a thread-specific data destructor function.

Associated Routines

pthread_key_create()
pthread_setspecific()

Obtains a value representing a desired expiration time.

Syntax

pthread_get_expiration_np(
delta ,
abstime );

Argument	Data Type	Access
delta	struct timespec	read
abstime	struct timespec	write

int
pthread_get_expiration_np (
const struct timespec *delta,
struct timespec *abstime);

Arguments

delta

Number of seconds and nanoseconds to add to the current system time. (The result is the time in the future.) This result will be placed in abstime.

abstime

Value representing the absolute expiration time. The absolute expiration time is obtained by adding delta to the current system time. The resulting abstime is in Universal Coordinated Time (UTC).

Description

This routine adds a specified interval to the current absolute system time and returns a new absolute time. This new absolute time may then be used as the expiration time in a call to pthread_cond_timedwait() .

The timespec structure contains the following two fields:

• tv_sec is an integral number of seconds.
• tv_nsec is an integral number of nanoseconds.

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

Associated Routines

pthread_cond_timedwait()

pthread_join32(), pthread_join64() The pthread_join32() and pthread_join64() forms are only valid in 64-bit pointer environments for OpenVMS Alpha. For information regarding 32- and 64-bit pointers, see Appendix B. Ensure that your compiler provides 64-bit support before you use pthread_join64() .

Causes the calling thread to wait for the termination of a specified thread.

Syntax

pthread_join(
thread ,
value _ptr );

Argument	Data Type	Access
thread	opaque pthread_t	read
value_ptr	void *	write

int
pthread_join (
pthread_t thread,
void **value_ptr);

Arguments

thread

Thread whose termination is awaited by the calling routine.

value_ptr

Return value of the terminating thread (when that thread either calls pthread_exit() or returns from its start routine).

Description

This routine suspends execution of the calling thread until the specified target thread thread terminates.

On return from a successful pthread_join() call with a non-NULL value_ptr argument, the value passed to pthread_exit() is returned in the location referenced by value_ptr, and the terminating thread is detached.

If more than one thread attempts to join with the same thread, the results are unpredictable.

A call to pthread_join() returns after the target thread terminates. The pthread_join() routine is a deferred cancelation point; the target thread will not be detached if the thread blocked in pthread_join() is canceled.

If a thread calls this routine and specifies its own pthread_t , a deadlock can result.

The pthread_join() (or pthread_detach() ) routine should eventually be called for every thread that is created with the detachstate attribute of its thread object set to PTHREAD_CREATE_JOINABLE , so that storage associated with the thread can be reclaimed.

Note For OpenVMS Alpha systems: The pthread_join() routine is defined to pthread_join64() if you compile using /pointer_size=long . If you do not specify /pointer_size , or if you specify /pointer_size=short , then pthread_join() is defined to be pthread_join32() . You can call pthread_join32() or pthread_join64() instead of pthread_join() . The pthread_join32() form returns a 32-bit void * value in the address to which value_ptr points. The pthread_join64() form returns a 64-bit void * value. You can call either, or you can call pthread_join() . Note that if you call pthread_join32() and the thread with which you join returns a 64-bit value, the high 32 bits of which are not 0 (zero), the Threads Library discards those high bits with no warning.

Associated Routines

pthread_cancel()
pthread_create()
pthread_detach()
pthread_exit()

Generates a unique thread-specific data key.

Syntax

pthread_key_create(
key ,
destructor );

Argument	Data Type	Access
key	opaque pthread_key_t	write
destructor	procedure	read

int
pthread_key_create (
pthread_key_t *key,
void (*destructor)(void *));

Arguments

key

Location where the new thread-specific data key will be stored.

destructor

Procedure called to destroy a thread-specific data value associated with the created key when the thread terminates. Note that the argument to the destructor for the user-specified routine is the non-NULL value associated with a key.

Description

This routine generates a unique, thread-specific data key that is visible to all threads in the process. The variable key provided by this routine is an opaque object used to locate thread-specific data. Although the same key value can be used by different threads, the values bound to the key by pthread_setspecific() are maintained on a per-thread basis and persist for the life of the calling thread. The initial value of the key in all threads is NULL.

The Threads Library imposes a maximum number of thread-specific data keys, equal to the symbolic constant PTHREAD_KEYS_MAX .

Thread-specific data allows client software to associate "static" information with the current thread. For example, where a routine declares a variable static in a single-threaded program, a multithreaded version of the program might create a thread-specific data key to store the same variable.

This routine generates and returns a new key value. The key reserves a cell within each thread. Each call to this routine creates a new cell that is unique within an application invocation. Keys must be generated from initialization code that is guaranteed to be called only once within each process. (See the pthread_once() description for more information.)

When a thread terminates, its thread-specific data is automatically destroyed; however, the key remains unless destroyed by a call to pthread_key_delete() . An optional destructor function can be associated with each key. At thread exit, if a key has a non-NULL destructor pointer, and the thread has a non-NULL value associated with that key, the destructor function is called with the current associated value as its sole argument. The order in which thread-specific data destructors are called at thread termination is undefined.

Before each destructor is called, the thread's value for the corresponding key is set to NULL. After the destructors have been called for all non-NULL values with associated destructors, if there are still some non-NULL values with associated destructors, then this sequence of actions is repeated. If there are still non-NULL values for any key with a destructor after four repetitions of this sequence, the thread is terminated. At this point, any key values that represent allocated heap will be lost. Note that this occurs only when a destructor performs some action that creates a new value for some key. Your program's destructor code should attempt to avoid this sort of circularity.

Associated Routines

pthread_getspecific()
pthread_key_delete()
pthread_once()
pthread_setspecific()

Deletes a thread-specific data key.

Syntax

pthread_key_delete(
key );

Argument	Data Type	Access
key	opaque pthread_key_t	write

int
pthread_key_delete (
pthread_key_t key);

Arguments

key

Context key to be deleted.

Description

This routine deletes the thread-specific data key specified by the key argument, which must have been previously returned by pthread_key_create() .

The thread-specific data values associated with key need not be NULL at the time this routine is called. The application must free any application storage or perform any cleanup actions for data structures related to the deleted key or associated thread-specific data in any threads. This cleanup can be done either before or after this routine is called.

Attempting to use the key after calling this routine results in unpredictable behavior.

No destructor functions are invoked by this routine. Any destructor functions that may have been associated with key shall no longer be called upon thread exit. pthread_key_delete() can be called from within destructor functions.

Associated Routines

pthread_exit()
pthread_getspecific()
pthread_key_create()

Obtains the object name from a thread-specific data key object.

Syntax

pthread_key_getname_np(
key ,
name ,
len );

Argument	Data Type	Access
key	opaque pthread_key_t	read
name	char	write
len	opaque size_t	read

int
pthread_key_getname_np (
pthread_key_t *key,
char *name,
size_t len);

Arguments

key

Address of the thread-specific data key object whose object name is to be obtained.

name

Location to store the obtained object name.

len

Length in bytes of buffer at the location specified by name.

Description

This routine copies the object name from the thread-specific data key object specified by the key argument to the buffer at the location specified by the name argument. Before calling this routine, your program must allocate the buffer indicated by name.

The object name is a C language string and provides an identifier that is meaningful to a person debugging a multithreaded application. The maximum number of characters in the object name is 31.

If the specified thread-specific data key object has not been previously set with an object name, this routine copies a C language null string into the buffer at location name.

Associated Routines

pthread_key_setname_np()

Changes the object name in a thread-specific data key object.

Syntax

pthread_key_setname_np(
key ,
name ,
mbz );

Argument	Data Type	Access
key	opaque pthread_key_t	write
name	char	read
mbz	void	read

int
pthread_key_setname_np (
pthread_key_t *cond,
const char *name,
void *mbz);

Arguments

key

Address of the thread-specific data key object whose object name is to be changed.

name

Object name value to copy into the key object.

mbz

Reserved for future use. The value must be zero (0).

Description

This routine changes the object name in the thread-specific data key object specified by the key argument to the value specified by the name argument. To set a new thread-specific data key object's object name, call this routine immediately after initializing the key object.

The object name is a C language string and provides an identifier that is meaningful to a person debugging a multithreaded application. The maximum number of characters in the object name is 31.

Associated Routines

pthread_key_getname_np()