NAME
pthread_rwlockattr_getpshared(), pthread_rwlockattr_setpshared() — get or set the process-shared attribute
SYNOPSIS
#include <pthread.h>
int pthread_rwlockattr_setpshared(pthread_rwlockattr_t *attr,
int pshared);
int pthread_rwlockattr_getpshared(const pthread_rwlockattr_t
*__restrict attr, int *__restrict pshared);
PARAMETERS
- attr
Pointer to the read-write lock attributes object whose attributes are to
be set/retrieved.
- pshared
This parameter either specifies the new value of the
process-shared
attribute (set function) or
points to the memory location where the
process-shared
attribute of
attr
is to be returned (get function).
DESCRIPTION
The attributes object
attr
must have been previously initialized with the
function
pthread_rwlockattr_init()
before these functions are called.
Read-Write locks can be used only by threads within the process or shared by
threads in multiple processes. The
process-shared
attribute in a read-write lock attributes object describes who may use
the read-write lock.
The legal values for the
process-shared
attribute are:
- PTHREAD_PROCESS_SHARED
This option permits a read-write lock to be operated upon by any thread
that has access
to the memory where the read-write lock is allocated.
The application is responsible for allocating the read-write lock in
memory that multiple processes can access.
- PTHREAD_PROCESS_PRIVATE
The read-write lock can only be operated upon by threads created within
the same process as the thread that initialized the read-write lock.
If threads of differing processes
attempt to operate on such read-write lock, the behavior is undefined.
The default value of
process-shared
is
PTHREAD_PROCESS_PRIVATE.
pthread_rwlockattr_setpshared()
is used to set the
process-shared
attribute in the initialized attributes object
attr.
The new value of the
process-shared
attribute of
attr
is set to the value specified in the
pshared
parameter.
pthread_rwlockattr_getpshared()
retrieves the value of the
process-shared
attribute from the read-write lock attributes object
attr.
The value of the
process-shared
attribute of
attr
is returned in the
pshared
parameter.
RETURN VALUE
Upon successful completion,
pthread_rwlockattr_getpshared()
and
pthread_rwlockattr_setpshared()
return zero. Otherwise, an error number is returned to indicate the error
(the
errno
variable is not set).
ERRORS
If any of the following occur, the
pthread_rwlockattr_getpshared()
and
pthread_rwlockattr_setpshared()
functions return the corresponding error number:
- ENOSYS
_POSIX_THREAD_PROCESS_SHARED
is not defined and these functions are not supported.
For each of the following conditions, if the condition is detected, the
pthread_rwlockattr_getpshared()
and
pthread_rwlockattr_setpshared()
functions return the corresponding error number:
- EINVAL
The value specified by
attr
is invalid.
- EINVAL
The value specified by
pshared
is not a legal value.
- EINVAL
The value
pshared
points to an illegal address.
WARNINGS
If a read-write lock is created with the
process-shared
attribute defined as
PTHREAD_PROCESS_SHARED,
the cooperating processes should have access to the memory in which the
read-write lock is allocated.
AUTHOR
pthread_rwlockattr_setpshared()
and
pthread_rwlockattr_getpshared()
were developed by X/Open.
STANDARDS CONFORMANCE
pthread_rwlockattr_setpshared(): X/Open.
pthread_rwlockattr_getpshared(): X/Open.
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