PTHREAD_ATTR_INIT

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
AUTHOR
SEE ALSO

NAME

pthread_attr_init, pthread_attr_destroy, pthread_attr_setdetachstate, pthread_attr_getdetachstate, pthread_attr_setschedparam, pthread_attr_getschedparam, pthread_attr_setschedpolicy, pthread_attr_getschedpolicy, pthread_attr_setinheritsched, pthread_attr_getinheritsched, pthread_attr_setscope, pthread_attr_getscope − thread creation attributes

SYNOPSIS

#include <pthread.h>

int pthread_attr_init(pthread_attr_t *attr);

int pthread_attr_destroy(pthread_attr_t *attr);

int pthread_attr_setdetachstate(pthread_attr_t *attr, int detachstate);

int pthread_attr_getdetachstate(const pthread_attr_t *attr, int *detachstate);

int pthread_attr_setschedpolicy(pthread_attr_t *attr, int policy);

int pthread_attr_getschedpolicy(const pthread_attr_t *attr, int *policy);

int pthread_attr_setschedparam(pthread_attr_t *attr, const struct sched_param *param);

int pthread_attr_getschedparam(const pthread_attr_t *attr, struct sched_param *param);

int pthread_attr_setinheritsched(pthread_attr_t *attr, int inherit);

int pthread_attr_getinheritsched(const pthread_attr_t *attr, int *inherit);

int pthread_attr_setscope(pthread_attr_t *attr, int scope);

int pthread_attr_getscope(const pthread_attr_t *attr, int *scope);

DESCRIPTION

Setting attributes for threads is achieved by filling a thread attribute object attr of type pthread_attr_t, then passing it as second argument to pthread_create(3). Passing NULL is equivalent to passing a thread attribute object with all attributes set to their default values.

pthread_attr_init initializes the thread attribute object attr and fills it with default values for the attributes. (The default values are listed below for each attribute.)

Each attribute attrname (see below for a list of all attributes) can be individually set using the function pthread_attr_setattrname and retrieved using the function pthread_attr_getattrname.

pthread_attr_destroy destroys a thread attribute object, which must not be reused until it is reinitialized. pthread_attr_destroy does nothing in the LinuxThreads implementation.

Attribute objects are consulted only when creating a new thread. The same attribute object can be used for creating several threads. Modifying an attribute object after a call to pthread_create does not change the attributes of the thread previously created.

The following thread attributes are supported:

detachstate

Control whether the thread is created in the joinable state (value PTHREAD_CREATE_JOINABLE) or in the detached state ( PTHREAD_CREATE_DETACHED).

Default value: PTHREAD_CREATE_JOINABLE.

In the joinable state, another thread can synchronize on the thread termination and recover its termination code using pthread_join(3), but some of the thread resources are kept allocated after the thread terminates, and reclaimed only when another thread performs pthread_join(3) on that thread.

In the detached state, the thread resources are immediately freed when it terminates, but pthread_join(3) cannot be used to synchronize on the thread termination.

A thread created in the joinable state can later be put in the detached thread using pthread_detach(3).

schedpolicy

Select the scheduling policy for the thread: one of SCHED_OTHER (regular, non-realtime scheduling), SCHED_RR (realtime, round-robin) or SCHED_FIFO (realtime, first-in first-out). See sched_setpolicy(2) for more information on scheduling policies.

Default value: SCHED_OTHER.

The realtime scheduling policies SCHED_RR and SCHED_FIFO are available only to processes with superuser privileges.

The scheduling policy of a thread can be changed after creation with pthread_setschedparam(3).

schedparam

Contain the scheduling parameters (essentially, the scheduling priority) for the thread. See sched_setparam(2) for more information on scheduling parameters.

Default value: priority is 0.

This attribute is not significant if the scheduling policy is SCHED_OTHER; it only matters for the realtime policies SCHED_RR and SCHED_FIFO.

The scheduling priority of a thread can be changed after creation with pthread_setschedparam(3).

inheritsched

Indicate whether the scheduling policy and scheduling parameters for the newly created thread are determined by the values of the schedpolicy and schedparam attributes (value PTHREAD_EXPLICIT_SCHED) or are inherited from the parent thread (value PTHREAD_INHERIT_SCHED).

Default value: PTHREAD_EXPLICIT_SCHED.

scope

Define the scheduling contention scope for the created thread. The only value supported in the LinuxThreads implementation is PTHREAD_SCOPE_SYSTEM, meaning that the threads contend for CPU time with all processes running on the machine. In particular, thread priorities are interpreted relative to the priorities of all other processes on the machine. The other value specified by the standard, PTHREAD_SCOPE_PROCESS, means that scheduling contention occurs only between the threads of the running process: thread priorities are interpreted relative to the priorities of the other threads of the process, regardless of the priorities of other processes. PTHREAD_SCOPE_PROCESS is not supported in LinuxThreads.

Default value: PTHREAD_SCOPE_SYSTEM.

RETURN VALUE

All functions return 0 on success and a non-zero error code on error. On success, the pthread_attr_getattrname functions also store the current value of the attribute attrname in the location pointed to by their second argument.

ERRORS

The pthread_attr_setdetachstate function returns the following error codes on error:

EINVAL

the specified detachstate is not one of

PTHREAD_CREATE_JOINABLE or PTHREAD_CREATE_DETACHED.

The pthread_attr_setschedparam function returns the following error codes on error:

EINVAL

the priority specified in param is outside the range of allowed priorities for the scheduling policy currently in attr (1 to 99 for SCHED_FIFO and SCHED_RR; 0 for SCHED_OTHER).

The pthread_attr_setschedpolicy function returns the following error codes on error:

EINVAL

the specified policy is not one of SCHED_OTHER, SCHED_FIFO, or SCHED_RR.

ENOTSUP

policy is SCHED_FIFO or SCHED_RR, and the effective user of the calling process is not super-user.

The pthread_attr_setinheritsched function returns the following error codes on error:

EINVAL

the specified inherit is not one of PTHREAD_INHERIT_SCHED or PTHREAD_EXPLICIT_SCHED.

The pthread_attr_setscope function returns the following error codes on error:

EINVAL

the specified scope is not one of PTHREAD_SCOPE_SYSTEM or PTHREAD_SCOPE_PROCESS.

ENOTSUP

the specified scope is PTHREAD_SCOPE_PROCESS (not supported).

AUTHOR

Xavier Leroy <Xavier.Leroy@inria.fr>

SEE ALSO

pthread_create(3), pthread_join(3), pthread_detach(3), pthread_setschedparam(3).