Updated: 11 December 1998

Guide to DECthreads

This appendix presents information that helps you migrate existing programs and applications that use the Compaq proprietary DECthreads CMA (or cma) interface to use the DECthreads pthread interface, based on the IEEE POSIX 1003.1c-1995 standard.

The DECthreads pthread interface differs significantly from the cma interface, though there are many similarities between the functions that individual routines perform. This section gives hints about the relationship between the two sets of routines, to assist you in migrating applications.

Note that routines whose names have the _np suffix are not portable---that is, the routine might not be available except in DECthreads.

You need not prototype the pthread routines if you include the C language pthread.h header file.

E.2 cma Handles

A cma handle is storage, similar to a pointer, that refers to a specific DECthreads object (thread, mutex, condition variable, queue, or attributes object).

Handles are allocated by the user application. They can be freely copied by the program and stored in any class of storage; objects are managed by DECthreads.

In the cma interface, because objects are accessed only by handles, you can think of the handle as if it were the object itself. DECthreads objects are accessed by handles (rather than pointers), because handles allow for greater robustness and portability. Handles allow DECthreads to detect the following types of run-time errors:

• Using an uninitialized handle
• Using a corrupted handle
• Using a handle whose object no longer exists (a dangling handle)

Handles are not supported in the DECthreads pthread interface. Although this provides less robustness due to more limited error checking, it allows better performance by decreasing memory use and memory access. (That is, handles result in pointers to pointers.)

E.3 Interface Routine Mapping

As summarized in Table E-1, many cma routines perform functions nearly identical to corresponding routines in the pthread interface. The syntax and semantics differ, but the similarities are also notable.

Table E-1 Corresponding cma and pthread Routines

cma Routine	pthread Routine	Notes
cma_alert_disable_asynch()	pthread_setcancelstate()/ pthread_setcanceltype()
cma_alert_disable_general()	pthread_setcancelstate()/ pthread_setcanceltype()
cma_alert_enable_asynch()	pthread_setcancelstate()/ pthread_setcanceltype()
cma_alert_enable_general()	pthread_setcancelstate()/ pthread_setcanceltype()
cma_alert_restore()	pthread_setcancelstate()/ pthread_setcanceltype()
cma_alert_test()	pthread_testcancel()
cma_attr_create()	pthread_attr_init()
cma_attr_delete()	pthread_attr_destroy()
cma_attr_get_guardsize()	pthread_attr_getguardsize_np()
cma_attr_get_inherit_sched()	pthread_attr_getinheritsched()
cma_attr_get_mutex_kind()	pthread_mutexattr_gettype_np()
cma_attr_get_priority()	pthread_attr_setsched_param()
cma_attr_get_sched()	pthread_attr_getschedpolicy()
cma_attr_get_stacksize()	pthread_attr_getstacksize()
cma_attr_set_guardsize()	pthread_attr_setguardsize_np()
cma_attr_set_inherit_sched()	pthread_attr_setinheritsched()
cma_attr_set_mutex_kind()	pthread_mutexattr_settype_np()
cma_attr_set_priority()	pthread_attr_setsched_param()
cma_attr_set_sched()	pthread_attr_setschedpolicy()
cma_attr_set_stacksize()	pthread_attr_setstacksize()
cma_cond_broadcast()	pthread_cond_broadcast()
cma_cond_create()	pthread_cond_init()
cma_cond_delete()	pthread_cond_destroy()
cma_cond_signal()	pthread_cond_signal()
cma_cond_signal_int()	pthread_cond_signal_int_np()
cma_cond_timed_wait()	pthread_cond_timedwait()
cma_cond_wait()	pthread_cond_wait()
cma_delay()	pthread_delay_np()
cma_handle_assign()	none	Use Language assignment operator.
cma_handle_equal()	pthread_equal()
cma_init()	none	Not necessary.
cma_key_create()	pthread_key_create() (Note: pthread_key_delete() is available as well.)
cma_key_get_context()	pthread_getspecific()
cma_key_set_context()	pthread_setspecific()
cma_lock_global()	pthread_lock_global_np()
cma_mutex_create()	pthread_mutex_init()
cma_mutex_delete()	pthread_mutex_delete()
cma_mutex_lock()	pthread_mutex_lock()
cma_mutex_try_lock()	pthread_mutex_trylock()
cma_mutex_unlock()	pthread_mutex_unlock()
cma_once()	pthread_once()
cma_stack_check_limit_np()
cma_thread_alert()	pthread_cancel()
cma_thread_bind_to_cpu()	none
cma_thread_create()	pthread_create()
cma_thread_detach()	pthread_detach()
cma_thread_exit_error()	pthread_exit()	With Status.
cma_thread_exit_normal()	pthread_exit()	With Status.
cma_thread_get_priority()	pthread_getschedparam()
cma_thread_get_sched()	pthread_setschedparam()
cma_thread_get_self()	pthread_self()
cma_thread_join()	pthread_join()
cma_thread_set_priority()	pthread_setschedparam()
cma_thread_set_sched()	pthread_setschedparam()
cma_time_get_expiration()	pthread_get_expiration_np()
cma_unlock_global()	pthread_unlock_global_np()
cma_yield()	pthread_yield()

Notice that the cma routine cma_cond_timed_wait() requires the time argument expiration to be specified in local time; whereas the pthread routine pthread_cond_timedwait() requires the time argument abstime to be specified in Universal Coordinated Time (UTC).

E.4 New pthread Routines

The following are pthread interface routines that have no functional similarities in the cma interface:

• pthread_atfork() (DIGITAL UNIX only)
• pthread_attr_getdetachstate()
• pthread_attr_setdetachstate()
• pthread_key_delete()
• pthread_kill() (DIGITAL UNIX only)
• pthread_sigmask() (DIGITAL UNIX only)

This appendix provides migration information for the routines in the DECthreads POSIX 1003.4a/Draft 4 (or d4) interface.

Routines in the DECthreads pthread interface differ significantly from the original DECthreads POSIX 1003.4a/Draft 4 implementation. This section describes the major changes between the interfaces.

F.2 Error Status and Function Returns

The DECthreads pthread interface does not use the global variable errno. (Note that DECthreads provides a thread-specific errno for use by libraries and application code, but the DECthreads pthread interface does not write to it.)

If an error condition occurs, a pthread routine returns an integer value that indicates the type of error. For example, a call to the DECthreads d4 interface's implementation of pthread_cond_destroy() that returned a --1 and set errno to [EBUSY], returns [EBUSY] as the routine's return value in the pthread interface implementation.

On successful completion, most pthread interface routines return zero (0).

F.3 Replaced or Renamed Routines

Many routines in the DECthreads d4 interface have been replaced or renamed in the pthread interface, as shown in Table F-1.

Table F-1 pthread Routines That Replace d4 Routines

d4 Routine	Replacement pthread Routine
pthread_attr_create()	pthread_attr_init()
pthread_attr_delete()	pthread_attr_destroy()
pthread_attr_set/getdetach_np()	pthread_attr_set/getdetachstate()
pthread_attr_set/getprio()	pthread_attr_set/getschedparam()
pthread_attr_set/getsched()	pthread_attr_set/getschedpolicy()
pthread_condattr_create()	pthread_condattr_init()
pthread_condattr_delete()	pthread_condattr_destroy()
pthread_keycreate()	pthread_key_create()
pthread_mutexattr_create()	pthread_mutexattr_init()
pthread_mutexattr_delete()	pthread_mutexattr_destroy()
pthread_mutexattr_get/setkind_np()	pthread_mutexattr_get/settype_np()
pthread_setasynccancel()	pthread_setcanceltype()
pthread_setcancel()	pthread_setcancelstate()
pthread_set/getprio()	pthread_set/getschedparam()
pthread_set/getscheduler()	pthread_set/getschedparam()
pthread_yield()	sched_yield()

F.4 Routines with No Changes to Syntax

Except for the return value, the following routines in the DECthreads d4 interface have no changes to syntax in the DECthreads pthread interface:

• pthread_attr_setinheritsched()
• pthread_cancel()
• pthread_cond_broadcast()
• pthread_cond_destroy()
• pthread_cond_signal()
• pthread_cond_signal_int_np()
• pthread_cond_timedwait()
• pthread_cond_wait()
• pthread_delay_np()
• pthread_equal()
• pthread_exit()
• pthread_get_expiration_np()
• pthread_join() (now detaches the thread)
• pthread_mutex_destroy()
• pthread_mutex_lock()
• pthread_mutex_trylock()
• pthread_mutex_unlock()
• pthread_once()

The following routines have no changes in syntax or return value:

• pthread_self()
• pthread_testcancel()

Notice that the d4 routine pthread_cond_timedwait() requires the time argument abstime to be specified in local time; whereas the pthread routine pthread_cond_timedwait() requires the time argument abstime to be specified in Universal Coordinated Time (UTC).

F.5 Routines with Prototype or Syntax Changes

Table F-2 shows the routines in the DECthreads d4 interface that have changes to their argument syntax in the DECthreads pthread interface.

Table F-2 d4 Routines With Syntax Changes as pthread Routines

Old Syntax	New Syntax
unsigned long pthread_attr_getguardsize_np( pthread_attr_t attr)	int pthread_attr_getguardsize_np( const pthread_attr_t * attr, size_t * guardsize)
int pthread_attr_getinheritsched( pthread_attr_t attr)	int pthread_attr_getinheritsched( const pthread_attr_t * attr, int * inheritsched)
unsigned long pthread_attr_getstacksize( pthread_attr_t attr)	int pthread_attr_getstacksize( const pthread_attr_t * attr, size_t * stacksize)
unsigned long pthread_attr_setguardsize_np( pthread_attr_t * attr, long guardsize)	int pthread_attr_setguardsize_np( pthread_attr_t * attr, size_t guardsize)
unsigned long pthread_attr_setstacksize( pthread_attr_t * attr, long stacksize)	int pthread_attr_setstacksize( const pthread_attr_t * attr, size_t stacksize)
int pthread_cleanup_pop( int execute)	void pthread_cleanup_pop( int execute)
int pthread_cond_init( pthread_cond_t * cond, pthread_condattr_t attr)	int pthread_cond_init( pthread_cond_t * cond, pthread_condattr_t * attr)
int pthread_create( pthread_t * thread, pthread_attr_t attr, pthread_startroutine_t start_routine, pthread_addr_t arg)	int pthread_create( pthread_t * thread, const pthread_attr_t * attr, void* (* start_routine)(void *), void * arg)
int pthread_detach( pthread_t * thread)	int pthread_detach( pthread_t thread)
int pthread_getspecific( pthread_key_t key, void ** value)	void * pthread_getspecific( pthread_key_t key)
void pthread_lock_global_np()	int pthread_lock_global_np(void)
void pthread_unlock_global_np()	int pthread_unlock_global_np(void)
int pthread_mutex_init( pthread_mutex_t * mutex, pthread_mutexattr_t attr)	int pthread_mutex_init( pthread_mutex_t * mutex, const pthread_mutexattr_t * attr)

Table F-3 shows routines in the DECthreads d4 interface that have a corresponding pthread routine that does not support the obsolete d4-style datatypes. These datatypes were documented for previous releases of DECthreads.

If your original code used the standard DECthreads datatypes, then this migration requirement might not impact your code.

Table F-3 d4 Routines Whose pthread Counterpart Uses Standard Datatypes

New Standard Datatype Syntax	Nonstandard Datatype Syntax
void pthread_cleanup_push( void (* routine)(void *), void * arg)	int pthread_cleanup_push( pthread_cleanup_t * routine, pthread_addr_t arg)
int pthread_create( pthread_t * thread, const pthread_attr_t * attr, void *(* start_routine)(void *), void * arg)	int pthread_create( pthread_t * thread, pthread_attr_t attr, pthread_startroutine_t start_routine, pthread_addr_t arg)
int pthread_exit( void * value_ptr)	int pthread_exit( pthread_addr_t status)
void * pthread_getspecific( pthread_key_t key)	int pthread_getspecific( pthread_key_t key, pthread_addr_t * value)
int pthread_join( pthread_t thread, void ** value_ptr)	int pthread_join( pthread_t thread, pthread_addr_t * status)
int pthread_once( pthread_once_t * once_control, void (* init_routine)(void))	int pthread_once( pthread_once_t * once_block, pthread_initroutine_t init_routine)
int pthread_setspecific( pthread_key_t key, const void * value)	int pthread_setspecific( pthread_key_t key, pthread_addr_t value)

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