HP OpenVMS Systems Documentation

Changes the object name in the thread object for an existing thread.

Syntax

pthread_setname_np(
thread ,
name ,
mbz );

Argument	Data Type	Access
thread	opaque pthread_thread_t	write
name	char	read
mbz	void	read

int
pthread_setname_np (
pthread_thread_t thread,
const char *name,
void *mbz);

Arguments

thread

Thread object whose object name is to be changed.

name

Object name value to copy into the thread object.

mbz

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

Description

This routine changes the object name in the thread object for the thread specified by the thread argument to the value specified by the name argument. To set an existing thread's object name, call this routine after creating the thread. However, with this approach your program must account for the possibility that the target thread either has already exited or has been canceled before this routine is called.

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.

This routine contrasts with pthread_attr_setname_np() , which changes the object name attribute in a thread attributes object that is used to create a new thread.

Associated Routines

pthread_attr_getname_np()
pthread_attr_setname_np()
pthread_getname_np()

Changes a thread's scheduling policy and scheduling parameters.

Syntax

pthread_setschedparam(
thread ,
policy ,
param );

Argument	Data Type	Access
thread	opaque pthread_t	read
policy	integer	read
param	struct sched_param	read

int
pthread_setschedparam (
pthread_t thread,
int policy,
const struct sched_param *param);

Arguments

thread

Thread whose scheduling policy and parameters are to be changed.

policy

New scheduling policy value for the thread specified in thread. The following are valid values:

SCHED_BG_NP
SCHED_FG_NP
SCHED_FIFO
SCHED_OTHER
SCHED_RR

See Section 2.3.2.2 for a description of thread scheduling policies.

param

New values of the scheduling parameters associated with the scheduling policy for the thread specified in thread. Valid values for the sched_priority field of a sched_param structure depend on the chosen scheduling policy. Use the POSIX routines sched_get_priority_min() or sched_get_priority_max() to determine the low and high limits of each policy.

Additionally, the Threads Librray provides nonportable priority range constants, as follows:

Low	High
PRI_FIFO_MIN	PRI_FIFO_MAX
PRI_RR_MIN	PRI_RR_MAX
PRI_OTHER_MIN	PRI_OTHER_MAX
PRI_FG_MIN_NP	PRI_FG_MAX_NP
PRI_BG_MIN_NP	PRI_BG_MAX_NP

The default priority varies by platform. On Tru64 UNIX, the default is 19 (that is, the POSIX priority of a normal timeshare process). On other platforms the default priority is the midpoint between PRI_FG_MIN_NP and PRI_FG_MAX_NP . ( Section 2.3.6 describes how to specify priorities between the minimum and maximum values.)

Description

This routine changes both the current scheduling policy and associated scheduling parameters of the thread specified by thread to the policy and associated parameters provided in policy and param, respectively.

All currently implemented scheduling policies have one scheduling parameter called sched_priority . For the policy you choose, you must specify an appropriate value in the sched_priority field of the sched_param structure.

Changing the scheduling policy or priority, or both, of a thread can cause it either to start executing or to be preempted by another thread. A thread changes its own scheduling policy and priority by using the handle returned by the pthread_self() routine.

This routine differs from pthread_attr_setschedpolicy() and
pthread_attr_setschedparam() , in that those routines set the scheduling policy and parameter attributes that are used to establish the scheduling priority and scheduling policy of a new thread when it is created. However, this routine changes the scheduling policy and parameters of an existing thread.

Associated Routines

pthread_attr_setschedparam()
pthread_attr_setschedpolicy()
pthread_create()
pthread_self()
sched_yield()

Sets the thread-specific data value associated with the specified key for the calling thread.

Syntax

pthread_setspecific(
key ,
value );

Argument	Data Type	Access
key	opaque pthread_key_t	read
value	void *	read

int
pthread_setspecific (
pthread_key_t key,
const void *value);

Arguments

key

Thread-specific key that identifies the thread-specific data to receive value. This key value must be obtained from pthread_key_create() .

value

New thread-specific data value to associate with the specified key for the calling thread.

Description

This routine sets the thread-specific data value associated with the specified key for the current thread. If a value is defined for the key in this thread (the current value is not NULL), the new value is substituted for it. The key is obtained by a previous call to pthread_key_create() .

Different threads can bind different values to the same key. These values are typically pointers to blocks of dynamically allocated memory that are reserved for use by the calling thread.

Do not call this routine from a thread-specific data destructor function.

Note that although the type for value (void *) implies that it represents an address, the type is being used as a "universal scalar type." The Threads Library simply stores value for later retrieval.

Associated Routines

pthread_getspecific()
pthread_key_create()
pthread_key_delete()

Examine or change the calling thread's signal mask.

This routine is for Tru64 UNIX systems only.

Syntax

pthread_sigmask(
how ,
set ,
oset );

Argument	Data Type	Access
how	integer	read
set	sigset_t	read
oset	sigset_t	write

int
pthread_sigmask (
int how,
const sigset_t *set,
sigset_t *oset);

Arguments

how

Indicates the manner in which the set of masked signals is changed. The optional values are as follows:

	SIG_BLOCK	The resulting set is the union of the current set and the signal set pointed to by the set argument.
	SIG_UNBLOCK	The resulting set is the intersection of the current set and the complement of the signal set pointed to by the set argument.
	SIG_SETMASK	The resulting set is the signal set pointed to by the set argument.

set

Specifies the signal set by pointing to a set of signals used to change the blocked set. If this set value is NULL, the how argument is ignored and the process signal mask is unchanged.

oset

Receives the value of the current signal mask (unless this value is NULL).

Description

This routine examines or changes the calling thread's signal mask. Typically, you use the SIG_BLOCK option for the how value to block signals during a critical section of code, and then use this routine's SIG_SETMASK option to restore the mask to the previous value returned by the previous call to the pthread_sigmask() routine.

If there are any unblocked signals pending after a call to this routine, at least one of those signals will be delivered before this routine returns.

This routine does not allow the SIGKILL or SIGSTOP signals to be blocked. If a program attempts to block one of these signals, pthread_sigmask() gives no indication of the error.

Requests delivery of a pending cancelation request to the calling thread.

Syntax

pthread_testcancel( );

void
pthread_testcancel (void);

Arguments

None

Description

This routine requests delivery of a pending cancelation request to the calling thread. Thus, calling this routine creates a cancelation point within the calling thread.

The cancelation request is delivered only if a request is pending for the calling thread and the calling thread's cancelability state is enabled. (A thread disables delivery of cancelation requests to itself by calling pthread_setcancelstate() .)

When called within very long loops, this routine ensures that a pending cancelation request is noticed by the calling thread within a reasonable amount of time.

Associated Routines

pthread_setcancelstate()

Unlocks the Threads Library global mutex.

Syntax

pthread_unlock_global_np( );

int
pthread_unlock_global_np (void);

Arguments

None

Description

This routine unlocks the Threads Library global mutex. Because the global mutex is recursive, the unlock occurs when each call to pthread_lock_global_np() has been matched by a call to this routine. For example, if you called pthread_lock_global_np() three times, pthread_unlock_global_np() unlocks the global mutex when you call it the third time.

If no threads are waiting for the global mutex, it becomes unlocked with no current owner. If one or more threads are waiting to lock the global mutex, this routine causes one thread to unblock and to try to acquire the global mutex. The scheduling policy is used by this routine to determine which thread is awakened. For the policies SCHED_FIFO and SCHED_RR , a blocked thread is chosen in priority order, using first-in/first-out (FIFO) within priorities.

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_lock_global_np()

Notifies the scheduler that the current thread is willing to release its processor to other threads of the same or higher priority.

Syntax

pthread_yield_np( );

Arguments

None

Description

This routine notifies the thread scheduler that the current thread is willing to release its processor to other threads of equivalent or greater scheduling precedence. (A thread generally will release its processor to a thread of a greater scheduling precedence without calling this routine.) If no other threads of equivalent or greater scheduling precedence are ready to execute, the thread continues.

This routine can allow knowledge of the details of an application to be used to improve its performance. If a thread does not call pthread_yield_np() , other threads may be given the opportunity to run at arbitrary points (possibly even when the interrupted thread holds a required resource). By making strategic calls to pthread_yield_np() , other threads can be given the opportunity to run when the resources are free. This improves performance by reducing contention for the resource.

As a general guideline, consider calling this routine after a thread has released a resource (such as a mutex) which is heavily contended for by other threads. This can be especially important either if the program is running on a uniprocessor machine, or if the thread acquires and releases the resource inside a tight loop.

Use this routine carefully and sparingly, because misuse can cause unnecessary context switching which will increase overhead and actually degrade performance. For example, it is counter-productive for a thread to yield while it holds a resource that the threads to which it is yielding will need. Likewise, it is pointless to yield unless there is likely to be another thread that is ready to run.

Note pthread_yield_np() is equivalent to sched_yield() . Use sched_yield() since it is part of the standard portable POSIX Threads Library.

Associated Routines

pthread_attr_setschedparam()
pthread_getschedparam()
pthread_setschedparam()

Returns the maximum priority for the specified scheduling policy.

Syntax

sched_get_priority_max(
policy );

Argument	Data Type	Access
policy	integer	read

int
sched_get_priority_max (
int policy);

Arguments

policy

One of the scheduling policies, as defined in sched.h .

Description

This routine returns the maximum priority for the scheduling policy specified in the policy argument. The argument value must be one of the scheduling policies ( SCHED_FIFO , SCHED_RR , or SCHED_OTHER ), as defined in the sched.h header file.

No special privileges are required to use this routine.