18. Thread Manager¶

18.2.1. Thread Attributes¶

Thread attributes are utilized only at thread creation time. A thread attribute structure may be initialized and passed as an argument to the pthread_create routine.

stack address

is the address of the optionally user specified stack area for this thread. If this value is NULL, then RTEMS allocates the memory for the thread stack from the RTEMS Workspace Area. Otherwise, this is the user specified address for the memory to be used for the thread’s stack. Each thread must have a distinct stack area. Each processor family has different alignment rules which should be followed.

stack size

is the minimum desired size for this thread’s stack area. If the size of this area as specified by the stack size attribute is smaller than the minimum for this processor family and the stack is not user specified, then RTEMS will automatically allocate a stack of the minimum size for this processor family.

contention scope

specifies the scheduling contention scope. RTEMS only supports the PTHREAD_SCOPE_PROCESS scheduling contention scope.

scheduling inheritance

specifies whether a user specified or the scheduling policy and parameters of the currently executing thread are to be used. When this is PTHREAD_INHERIT_SCHED, then the scheduling policy and parameters of the currently executing thread are inherited by the newly created thread.

scheduling policy and parameters

specify the manner in which the thread will contend for the processor. The scheduling parameters are interpreted based on the specified policy. All policies utilize the thread priority parameter.

18.4.1. pthread_attr_init - Initialize a Thread Attribute Set¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_init(
    pthread_attr_t *attr
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_init routine initializes the thread attributes object specified by attr with the default value for all of the individual attributes.

NOTES:

The settings in the default attributes are implementation defined. For RTEMS, the default attributes are as follows:

18.4.2. pthread_attr_destroy - Destroy a Thread Attribute Set¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_destroy(
    pthread_attr_t *attr
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_destroy routine is used to destroy a thread attributes object. The behavior of using an attributes object after it is destroyed is implementation dependent.

NOTES:

NONE

18.4.3. pthread_attr_setdetachstate - Set Detach State¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_setdetachstate(
    pthread_attr_t *attr,
    int             detachstate
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_setdetachstate routine is used to value of the detachstate attribute. This attribute controls whether the thread is created in a detached state.

The detachstate can be either PTHREAD_CREATE_DETACHED or PTHREAD_CREATE_JOINABLE. The default value for all threads is PTHREAD_CREATE_JOINABLE.

NOTES:

If a thread is in a detached state, then the use of the ID with the pthread_detach or pthread_join routines is an error.

18.4.4. pthread_attr_getdetachstate - Get Detach State¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_getdetachstate(
    const pthread_attr_t *attr,
    int                  *detachstate
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_getdetachstate routine is used to obtain the current value of the detachstate attribute as specified by the attr thread attribute object.

NOTES:

NONE

18.4.5. pthread_attr_setstacksize - Set Thread Stack Size¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_setstacksize(
    pthread_attr_t *attr,
    size_t          stacksize
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_setstacksize routine is used to set the stacksize attribute in the attr thread attribute object.

NOTES:

As required by POSIX, RTEMS defines the feature symbol _POSIX_THREAD_ATTR_STACKSIZE to indicate that this routine is supported.

If the specified stacksize is below the minimum required for this CPU (PTHREAD_STACK_MIN, then the stacksize will be set to the minimum for this CPU.

18.4.6. pthread_attr_getstacksize - Get Thread Stack Size¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_getstacksize(
    const pthread_attr_t *attr,
    size_t               *stacksize
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_getstacksize routine is used to obtain the stacksize attribute in the attr thread attribute object.

NOTES:

As required by POSIX, RTEMS defines the feature symbol _POSIX_THREAD_ATTR_STACKSIZE to indicate that this routine is supported.

18.4.7. pthread_attr_setstackaddr - Set Thread Stack Address¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_setstackaddr(
    pthread_attr_t *attr,
    void           *stackaddr
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_setstackaddr routine is used to set the stackaddr attribute in the attr thread attribute object.

NOTES:

As required by POSIX, RTEMS defines the feature symbol _POSIX_THREAD_ATTR_STACKADDR to indicate that this routine is supported.

It is imperative to the proper operation of the system that each thread have sufficient stack space.

18.4.8. pthread_attr_getstackaddr - Get Thread Stack Address¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_getstackaddr(
    const pthread_attr_t  *attr,
    void                 **stackaddr
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_getstackaddr routine is used to obtain the stackaddr attribute in the attr thread attribute object.

NOTES:

As required by POSIX, RTEMS defines the feature symbol _POSIX_THREAD_ATTR_STACKADDR to indicate that this routine is supported.

18.4.9. pthread_attr_setscope - Set Thread Scheduling Scope¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_setscope(
    pthread_attr_t *attr,
    int             contentionscope
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_setscope routine is used to set the contention scope field in the thread attribute object attr to the value specified by contentionscope.

The contentionscope must be either PTHREAD_SCOPE_SYSTEM to indicate that the thread is to be within system scheduling contention or PTHREAD_SCOPE_PROCESS indicating that the thread is to be within the process scheduling contention scope.

NOTES:

As required by POSIX, RTEMS defines the feature symbol _POSIX_THREAD_PRIORITY_SCHEDULING to indicate that the family of routines to which this routine belongs is supported.

18.4.10. pthread_attr_getscope - Get Thread Scheduling Scope¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_getscope(
    const pthread_attr_t *attr,
    int                  *contentionscope
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_getscope routine is used to obtain the value of the contention scope field in the thread attributes object attr. The current value is returned in contentionscope.

NOTES:

As required by POSIX, RTEMS defines the feature symbol _POSIX_THREAD_PRIORITY_SCHEDULING to indicate that the family of routines to which this routine belongs is supported.

18.4.11. pthread_attr_setinheritsched - Set Inherit Scheduler Flag¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_setinheritsched(
    pthread_attr_t *attr,
    int             inheritsched
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_setinheritsched routine is used to set the inherit scheduler field in the thread attribute object attr to the value specified by inheritsched.

The contentionscope must be either PTHREAD_INHERIT_SCHED to indicate that the thread is to inherit the scheduling policy and parameters fromthe creating thread, or PTHREAD_EXPLICIT_SCHED to indicate that the scheduling policy and parameters for this thread are to be set from the corresponding values in the attributes object. If contentionscope is PTHREAD_INHERIT_SCHED, then the scheduling attributes in the attr structure will be ignored at thread creation time.

NOTES:

As required by POSIX, RTEMS defines the feature symbol _POSIX_THREAD_PRIORITY_SCHEDULING to indicate that the family of routines to which this routine belongs is supported.

18.4.12. pthread_attr_getinheritsched - Get Inherit Scheduler Flag¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_getinheritsched(
    const pthread_attr_t *attr,
    int                  *inheritsched
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_getinheritsched routine is used to object the current value of the inherit scheduler field in the thread attribute object attr.

NOTES:

As required by POSIX, RTEMS defines the feature symbol _POSIX_THREAD_PRIORITY_SCHEDULING to indicate that the family of routines to which this routine belongs is supported.

18.4.13. pthread_attr_setschedpolicy - Set Scheduling Policy¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_setschedpolicy(
    pthread_attr_t *attr,
    int             policy
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_setschedpolicy routine is used to set the scheduler policy field in the thread attribute object attr to the value specified by policy.

Scheduling policies may be one of the following:

• SCHED_DEFAULT
• SCHED_FIFO
• SCHED_RR
• SCHED_SPORADIC
• SCHED_OTHER

The precise meaning of each of these is discussed elsewhere in this manual.

NOTES:

As required by POSIX, RTEMS defines the feature symbol _POSIX_THREAD_PRIORITY_SCHEDULING to indicate that the family of routines to which this routine belongs is supported.

18.4.14. pthread_attr_getschedpolicy - Get Scheduling Policy¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_getschedpolicy(
    const pthread_attr_t *attr,
    int                  *policy
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_getschedpolicy routine is used to obtain the scheduler policy field from the thread attribute object attr. The value of this field is returned in policy.

NOTES:

As required by POSIX, RTEMS defines the feature symbol _POSIX_THREAD_PRIORITY_SCHEDULING to indicate that the family of routines to which this routine belongs is supported.

18.4.15. pthread_attr_setschedparam - Set Scheduling Parameters¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_setschedparam(
    pthread_attr_t           *attr,
    const struct sched_param  param
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_setschedparam routine is used to set the scheduler parameters field in the thread attribute object attr to the value specified by param.

NOTES:

As required by POSIX, RTEMS defines the feature symbol _POSIX_THREAD_PRIORITY_SCHEDULING to indicate that the family of routines to which this routine belongs is supported.

18.4.16. pthread_attr_getschedparam - Get Scheduling Parameters¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_attr_getschedparam(
    const pthread_attr_t *attr,
    struct sched_param   *param
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_getschedparam routine is used to obtain the scheduler parameters field from the thread attribute object attr. The value of this field is returned in param.

NOTES:

As required by POSIX, RTEMS defines the feature symbol _POSIX_THREAD_PRIORITY_SCHEDULING to indicate that the family of routines to which this routine belongs is supported.

18.4.17. pthread_attr_getaffinity_np - Get Thread Affinity Attribute¶

CALLING SEQUENCE:

#define _GNU_SOURCE
#include <pthread.h>
int pthread_attr_getaffinity_np(
    const pthread_attr_t *attr,
    size_t                cpusetsize,
    cpu_set_t            *cpuset
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_getaffinity_np routine is used to obtain the affinityset field from the thread attribute object attr. The value of this field is returned in cpuset.

NOTES:

NONE

18.4.18. pthread_attr_setaffinity_np - Set Thread Affinity Attribute¶

CALLING SEQUENCE:

#define _GNU_SOURCE
#include <pthread.h>
int pthread_attr_setaffinity_np(
    pthread_attr_t    *attr,
    size_t             cpusetsize,
    const cpu_set_t   *cpuset
);

STATUS CODES:

DESCRIPTION:

The pthread_attr_setaffinity_np routine is used to set the affinityset field in the thread attribute object attr. The value of this field is returned in cpuset.

NOTES:

NONE

18.4.19. pthread_create - Create a Thread¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_create(
    pthread_t             *thread,
    const pthread_attr_t  *attr,
    void                 (*start_routine)( void *),
    void                  *arg
);

STATUS CODES:

DESCRIPTION:

The pthread_create routine is used to create a new thread with the attributes specified by attr. If the attr argument is NULL, then the default attribute set will be used. Modification of the contents of attr after this thread is created does not have an impact on this thread.

The thread begins execution at the address specified by start_routine with arg as its only argument. If start_routine returns, then it is functionally equivalent to the thread executing the pthread_exit service.

Upon successful completion, the ID of the created thread is returned in the thread argument.

NOTES:

There is no concept of a single main thread in RTEMS as there is in a tradition UNIX system. POSIX requires that the implicit return of the main thread results in the same effects as if there were a call to exit. This does not occur in RTEMS.

The signal mask of the newly created thread is inherited from its creator and the set of pending signals for this thread is empty.

18.4.20. pthread_exit - Terminate the Current Thread¶

CALLING SEQUENCE:

#include <pthread.h>
void pthread_exit(
    void *status
);

STATUS CODES:

NONE

DESCRIPTION:

The pthread_exit routine is used to terminate the calling thread. The status is made available to any successful join with the terminating thread.

When a thread returns from its start routine, it results in an implicit call to the pthread_exit routine with the return value of the function serving as the argument to pthread_exit.

NOTES:

Any cancellation cleanup handlers that hace been pushed and not yet popped shall be popped in reverse of the order that they were pushed. After all cancellation cleanup handlers have been executed, if the thread has any thread-specific data, destructors for that data will be invoked.

Thread termination does not release or free any application visible resources including byt not limited to mutexes, file descriptors, allocated memory, etc.. Similarly, exitting a thread does not result in any process-oriented cleanup activity.

There is no concept of a single main thread in RTEMS as there is in a tradition UNIX system. POSIX requires that the implicit return of the main thread results in the same effects as if there were a call to exit. This does not occur in RTEMS.

All access to any automatic variables allocated by the threads is lost when the thread exits. Thus references (i.e. pointers) to local variables of a thread should not be used in a global manner without care. As a specific example, a pointer to a local variable should NOT be used as the return value.

18.4.21. pthread_detach - Detach a Thread¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_detach(
    pthread_t thread
);

STATUS CODES:

DESCRIPTION:

The pthread_detach routine is used to to indicate that storage for thread can be reclaimed when the thread terminates without another thread joinging with it.

NOTES:

If any threads have previously joined with the specified thread, then they will remain joined with that thread. Any subsequent calls to pthread_join on the specified thread will fail.

18.4.22. pthread_getattr_np - Get Thread Attributes¶

CALLING SEQUENCE:

#define _GNU_SOURCE
#include <pthread.h>
int pthread_getattr_np(
    pthread_t       thread,
    pthread_attr_t *attr
);

STATUS CODES:

DESCRIPTION:

The pthread_getattr_np routine is used to obtain the attributes associated with thread.

NOTES:

Modification of the execution modes and priority through the Classic API may result in a combination that is not representable in the POSIX API.

18.4.23. pthread_join - Wait for Thread Termination¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_join(
    pthread_t    thread,
    void       **value_ptr
);

STATUS CODES:

DESCRIPTION:

The pthread_join routine suspends execution of the calling thread until thread terminates. If thread has already terminated, then this routine returns immediately. The value returned by thread (i.e. passed to pthread_exit is returned in value_ptr.

When this routine returns, then thread has been terminated.

NOTES:

The results of multiple simultaneous joins on the same thread is undefined.

If any threads have previously joined with the specified thread, then they will remain joined with that thread. Any subsequent calls to pthread_join on the specified thread will fail.

If value_ptr is NULL, then no value is returned.

18.4.24. pthread_self - Get Thread ID¶

CALLING SEQUENCE:

#include <pthread.h>
pthread_t pthread_self( void );

STATUS CODES:

The value returned is the ID of the calling thread.

DESCRIPTION:

This routine returns the ID of the calling thread.

NOTES:

NONE

18.4.25. pthread_equal - Compare Thread IDs¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_equal(
    pthread_t t1,
    pthread_t t2
);

STATUS CODES:

DESCRIPTION:

The pthread_equal routine is used to compare two thread IDs and determine if they are equal.

NOTES:

The behavior is undefined if the thread IDs are not valid.

18.4.26. pthread_once - Dynamic Package Initialization¶

CALLING SEQUENCE:

#include <pthread.h>
pthread_once_t once_control = PTHREAD_ONCE_INIT;
int pthread_once(
    pthread_once_t   *once_control,
    void            (*init_routine)(void)
);

STATUS CODES:

NONE

DESCRIPTION:

The pthread_once routine is used to provide controlled initialization of variables. The first call to pthread_once by any thread with the same once_control will result in the init_routine being invoked with no arguments. Subsequent calls to pthread_once with the same once_control will have no effect.

The init_routine is guaranteed to have run to completion when this routine returns to the caller.

NOTES:

The behavior of pthread_once is undefined if once_control is automatic storage (i.e. on a task stack) or is not initialized using PTHREAD_ONCE_INIT.

18.4.27. pthread_setschedparam - Set Thread Scheduling Parameters¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_setschedparam(
    pthread_t           thread,
    int                 policy,
    struct sched_param *param
);

STATUS CODES:

DESCRIPTION:

The pthread_setschedparam routine is used to set the scheduler parameters currently associated with the thread specified by thread to the policy specified by policy. The contents of param are interpreted based upon the policy argument.

NOTES:

As required by POSIX, RTEMS defines the feature symbol _POSIX_THREAD_PRIORITY_SCHEDULING to indicate that the family of routines to which this routine belongs is supported.

18.4.28. pthread_getschedparam - Get Thread Scheduling Parameters¶

CALLING SEQUENCE:

#include <pthread.h>
int pthread_getschedparam(
    pthread_t           thread,
    int                *policy,
    struct sched_param *param
);

STATUS CODES:

DESCRIPTION:

The pthread_getschedparam routine is used to obtain the scheduler policy and parameters associated with thread. The current policy and associated parameters values returned in``policy`` and param, respectively.

NOTES:

As required by POSIX, RTEMS defines the feature symbol _POSIX_THREAD_PRIORITY_SCHEDULING to indicate that the family of routines to which this routine belongs is supported.

18.4.29. pthread_getaffinity_np - Get Thread Affinity¶

CALLING SEQUENCE:

#define _GNU_SOURCE
#include <pthread.h>
int pthread_getaffinity_np(
    const pthread_t       id,
    size_t                cpusetsize,
    cpu_set_t            *cpuset
);

STATUS CODES:

DESCRIPTION:

The pthread_getaffinity_np routine is used to obtain the affinity.set field from the thread control object associated with the id. The value of this field is returned in cpuset.

NOTES:

NONE

18.4.30. pthread_setaffinity_np - Set Thread Affinity¶

CALLING SEQUENCE:

#define _GNU_SOURCE
#include <pthread.h>
int pthread_setaffinity_np(
    pthread_t          id,
    size_t             cpusetsize,
    const cpu_set_t   *cpuset
);

STATUS CODES:

DESCRIPTION:

The pthread_setaffinity_np routine is used to set the affinityset field of the thread object id. The value of this field is returned in cpuset

NOTES:

NONE