Updated: 11 December 1998

Guide to DECthreads

Suspends a calling thread until a signal arrives.

Syntax

sigwait(
set ,
signal );

Argument	Data Type	Access
set	sigset_t	read
signal	integer	write

C Binding

Arguments

set

Set of signals to wait for.

signal

Signal number obtained for the selected signal.

Description

This routine suspends the calling thread until at least one of the signals in the set argument is in the caller's set of pending signals. When this happens, one of those signals is automatically selected and removed from the set of pending signals. The signal number identifying that signal is then returned.

This routine stores the signal number obtained in the address specified in the signal argument.

The effect of calling this routine is unspecified if any signals in the set argument are not blocked at the time of the call.

The set signal set object is created using the set manipulation routines sigemptyset(), sigfillset(), sigaddset(), and sigdelset().

If, while this routine is waiting, a signal occurs that is eligible for delivery (that is, not blocked by the signal mask), that signal is handled asynchronously and the wait is interrupted.

Return Values

Associated Routines

• sigaddset()
• sigdelset()
• sigemptyset()
• sigfillset()
• sigaction()
• sigpending()
• sigsuspend()

These routines are designed to provide efficient tools for thread safety in libraries whose routines do not themselves use threads. The tis interface provides functions identical to several pthread functions. In a program that creates or uses threads, the tis functions provide full thread synchronization and coherence of memory access. But, in a program that does not use threads, the same tis calls provide low-overhead "stub" implementations of pthread features.

The objects created using tis interface routines are the same as pthread interface objects.

The variable errno is not used by the tis routines. Like the pthread routines, the tis routines return integer values indicating the type of error.

When threads are present, the guidelines for using pthread routines apply to using the corresponding tis routines.

Wakes all threads that are waiting on a condition variable.

Syntax

tis_cond_broadcast(
cond );

Argument	Data Type	Access
cond	opaque pthread_cond_t	modify

C Binding

Arguments

cond

Address of the condition variable (passed by reference) on which to broadcast.

Description

When threads are not present, this routine performs no actions.

When threads are present, this routine unblocks all threads waiting on the specified condition variable cond.

For further information about actions when threads are present, refer to the pthread_cond_broadcast() description.

Return Values

Associated Routines

• tis_cond_destroy()
• tis_cond_init()
• tis_cond_signal()
• tis_cond_wait()

Destroys the specified condition variable.

Syntax

tis_cond_destroy(
cond );

Argument	Data Type	Access
cond	opaque pthread_cond_t	write

C Binding

Arguments

cond

Address of the condition variable (passed by reference) to be destroyed.

Description

This routine destroys the condition variable specified by cond. After this routine is called, DECthreads may reclaim internal storage used by the condition variable object. Call this routine when a condition variable will no longer be referenced.

The results of this routine are unpredictable, if the condition variable specified in cond does not exist or is not initialized.

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

Return Values

Associated Routines

• tis_cond_broadcast()
• tis_cond_init()
• tis_cond_signal()
• tis_cond_wait()

Initializes a condition variable.

Syntax

tis_cond_init(
cond );

Argument	Data Type	Access
cond	opaque pthread_cond_t	write

C Binding

Arguments

cond

Address of the condition variable (passed by reference) to be initialized.

Description

This routine initializes a condition variable (cond) with the DECthreads default condition variable attributes.

A condition variable is a synchronization object used in conjunction with a mutex. A mutex controls access to shared data. When threads are present, a condition variable allows threads to wait for data to enter a defined state.

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

Your program can use the macro PTHREAD_COND_INITIALIZER to initialize statically allocated condition variables to the DECthreads default condition variable attributes. Use this macro as follows:
pthread_cond_t condition = PTHREAD_COND_INITIALIZER;

When statically initialized, a condition variable should not also be initialized using tis_cond_init(). Also, a statically initialized condition variable need not be destroyed using tis_cond_destroy().

Return Values

• The routine returns an integer value indicating the type of error.
• The condition variable is not initialized.
• The contents of conditon variable cond are undefined.

Associated Routines

• tis_cond_broadcast()
• tis_cond_destroy()
• tis_cond_signal()
• tis_cond_wait()

Wakes at least one thread that is waiting on the specified condition variable.

Syntax

tis_cond_signal(
cond );

Argument	Data Type	Access
cond	opaque pthread_cond_t	modify

C Binding

Arguments

cond

Address of the condition variable (passed by reference) on which to signal.

Description

When threads are present, this routine unblocks at least one thread that is waiting on the specified condition variable cond.

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

Return Values

Associated Routines

• tis_cond_broadcast()
• tis_cond_destroy()
• tis_cond_init()
• tis_cond_wait()

Causes a thread to wait for the specified condition variable to be signaled or broadcasted.

Syntax

tis_cond_wait(
cond ,
mutex );

Argument	Data Type	Access
cond	opaque pthread_cond_t	modify
mutex	opaque pthread_mutex_t	modify

C Binding

Arguments

cond

Address of the condition variable (passed by reference) on which to wait.

mutex

Address of the mutex (passed by reference) that is associated with the condition variable specified in cond.

Description

When threads are present, this routine causes a thread to wait for the specified condition variable cond to be signaled or broadcasted.

Calling this routine in a single-threaded environment is a coding error. Because no thread can execute in parallel to issue a call to tis_cond_signal() or tis_cond_broadcast(), using this routine in a single-threaded environment forces the program to exit.

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

Return Values

Associated Routines

• tis_cond_broadcast()
• tis_cond_destroy()
• tis_cond_init()
• tis_cond_signal()

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

Syntax

tis_getspecific(
key );

Argument	Data Type	Access
key	opaque pthread_key_t	read

C Binding

Arguments

key

Identifies a value returned by a call to tis_key_create(). This routine returns the data value associated with the thread-specific data key.

Description

This routine returns the value currently bound to the specified thread-specific data key.

This routine can be called from a data destructor function.

When threads are present, the data and keys are thread specific; they enable a library to maintain context on a per-thread basis.

Return Values

Associated Routines

• tis_key_create()
• tis_key_delete()
• tis_setspecific()

Generates a unique thread-specific data key.

Syntax

tis_key_create(
key ,
destructor );

Argument	Data Type	Access
key	opaque pthread_key_t	write
destructor	procedure	read

C Binding

Arguments

key

Address of a variable that receives the key value. This value is used in calls to tis_getspecific() and tis_setspecific() to get and set the value associated with this key.

destructor

Address of a routine that is called to destroy the context value when a thread terminates with a non-NULL value for the key. Note that this argument is used only when threads are present.

Description

This routine generates a unique thread-specific data key. The key argument points to an opaque object used to locate data.

This routine generates and returns a new key value. The key reserves a cell. 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 tis_once() description for more information.)

Your program can associate an optional destructor function with each key. At thread exit, if a key has a non-NULL destructor function pointer, and the thread has a non-NULL value associated with that key, the function pointed to is called with the current associated value as its sole argument. The order in which data destructors are called at thread termination is undefined.

When threads are present, keys and any corresponding data are thread specific; they enable the context to be maintained on a per-thread basis. For more information about the use of tis_key_create() in a threaded environment, refer to the pthread_key_create() description.

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

Return Values

Associated Routines

• tis_getspecific()
• tis_key_delete()
• tis_setspecific()
• tis_once()

Deletes the specified thread-specific data key.

Syntax

tis_key_delete(
key );

Argument	Data Type	Access
key	opaque pthread_key_t	write

C Binding

Arguments

key

Thread-specific data key to be deleted.

Description

This routine deletes a thread-specific data key key previously returned by a call to the tis_key_create() routine. The 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 data. This cleanup can be done before or after this routine is called.

Attempting to use the thread-specific data key 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 will no longer be called upon thread exit.

This routine can be called from destructor functions.

Return Values

Associated Routines

• tis_getspecific()
• tis_key_create()
• tis_setspecific()

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