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NAME
threads, pthreads, libpthread, libthread - concepts related
to POSIX pthreads and Solaris threads and the libpthread and
libthread libraries
SYNOPSIS
POSIX
cc -mt [ flag... ] file...- lpthread [ -lposix4 library... ]
#include <pthread.h>
Solaris
cc - mt [ flag... ] file...[ library... ]
#include <sched.h>
#include <thread.h>
DESCRIPTION
POSIX and Solaris threads each have their own implementation
of the threads library. The libpthread library is associ-
ated with POSIX; the libthread library is associated with
Solaris. Both implementations are interoperable, their func-
tionality similar, and can be used within the same applica-
tion. Only POSIX threads are guaranteed to be fully portable
to other POSIX-compliant environments. POSIX and Solaris
threads require different source, include files and linking
libraries. See SYNOPSIS.
Similarities
Most of the functions in the libpthread and libthread,
libraries have a counterpart in the other corresponding
library. POSIX function names, with the exception of the
semaphore names, have a "pthread" prefix. Function names for
similar POSIX and Solaris have similar endings. Typically,
similar POSIX and Solaris functions have the same number and
use of arguments.
Differences
POSIX pthreads and Solaris threads differ in the following
ways:
o POSIX threads are more portable.
o POSIX threads establish characteristics for each
thread according to configurable attribute objects.
o POSIX pthreads implement thread cancellation.
o POSIX pthreads enforce scheduling algorithms.
o POSIX pthreads allow for clean-up handlers for fork(2)
calls.
o Solaris threads can be suspended and continued.
o Solaris threads implement an optimized mutex and
interprocess robust mutex locks.
o Solaris threads implement daemon threads, for whose
demise the process does not wait.
Function Comparison
The following table compares the POSIX pthreads and Solaris
threads functions. When a comparable interface is not avail-
able either in POSIX pthreads or Solaris threads, a hyphen
(-) appears in the column.
Functions Related to Creation
POSIX (libpthread) Solaris (libthread)
pthread_create() thr_create()
pthread_attr_init() -
pthread_attr_setdetachstate() -
pthread_attr_getdetachstate() -
pthread_attr_setinheritsched() -
pthread_attr_getinheritsched() -
pthread_attr_setschedparam() -
pthread_attr_getschedparam() -
pthread_attr_setschedpolicy() -
pthread_attr_getschedpolicy() -
pthread_attr_setscope() -
pthread_attr_getscope() -
pthread_attr_setstackaddr() -
pthread_attr_getstackaddr() -
pthread_attr_setstacksize() -
pthread_attr_getstacksize() -
pthread_attr_getguardsize() -
pthread_attr_setguardsize() -
pthread_attr_destroy() -
- thr_min_stack()
Functions Related to Exit
POSIX (libpthread) Solaris (libthread)
pthread_exit() thr_exit()
pthread_join() thr_join()
pthread_detach() -
Functions Related to Thread Specific Data
POSIX (libpthread) Solaris (libthread)
pthread_key_create() thr_keycreate()
pthread_setspecific() thr_setspecific()
pthread_getspecific() thr_getspecific()
pthread_key_delete() -
Functions Related to Signals
POSIX (libpthread) Solaris (libthread)
pthread_sigmask() thr_sigsetmask()
pthread_kill() thr_kill()
Functions Related to IDs
POSIX (libpthread) Solaris (libthread)
pthread_self() thr_self()
pthread_equal() -
- thr_main()
Functions Related to Scheduling
POSIX (libpthread) Solaris (libthread)
- thr_yield()
- thr_suspend()
- thr_continue()
pthread_setconcurrency() thr_setconcurrency()
pthread_getconcurrency() thr_getconcurrency()
pthread_setschedparam() thr_setprio()
pthread_getschedparam() thr_getprio()
Functions Related to Cancellation
POSIX (libpthread) Solaris (libthread)
pthread_cancel() -
pthread_setcancelstate() -
pthread_setcanceltype() -
pthread_testcancel() -
pthread_cleanup_pop() -
pthread_cleanup_push() -
Functions Related to Mutexes
POSIX (libpthread) Solaris (libthread)
pthread_mutex_init() mutex_init()
pthread_mutexattr_init() -
pthread_mutexattr_setpshared() -
pthread_mutexattr_getpshared() -
pthread_mutexattr_setprotocol() -
pthread_mutexattr_getprotocol() -
pthread_mutexattr_setprioceiling() -
pthread_mutexattr_getprioceiling() -
pthread_mutexattr_settype() -
pthread_mutexattr_gettype() -
pthread_mutexattr_destroy() -
pthread_mutex_setprioceiling() -
pthread_mutex_getprioceiling() -
pthread_mutex_lock() mutex_lock()
pthread_mutex_trylock() mutex_trylock()
pthread_mutex_unlock() mutex_unlock()
pthread_mutex_destroy() mutex_destroy()
Functions Related to Condition Variables
POSIX (libpthread) Solaris (libthread)
pthread_cond_init() cond_init()
pthread_condattr_init() -
pthread_condattr_setpshared() -
pthread_condattr_getpshared() -
pthread_condattr_destroy() -
pthread_cond_wait() cond_wait()
pthread_cond_timedwait() cond_timedwait()
pthread_cond_signal() cond_signal()
pthread_cond_broadcast() cond_broadcast()
pthread_cond_destroy() cond_destroy()
Functions Related to Reader/Writer Locking
POSIX (libpthread) Solaris (libthread)
pthread_rwlock_init() rwlock_init()
pthread_rwlock_rdlock() rw_rdlock()
pthread_rwlock_tryrdlock() rw_tryrdlock()
pthread_rwlock_wrlock() rw_wrlock()
pthread_rwlock_trywrlock() rw_trywrlock()
pthread_rwlock_unlock() rw_unlock()
pthread_rwlock_destroy() rwlock_destroy()
pthread_rwlockattr_init() -
pthread_rwlockattr_destroy() -
pthread_rwlockattr_getpshared() -
pthread_rwlockattr_setpshared() -
Functions Related to Semaphores
POSIX (libpthread) Solaris (libthread)
sem_init() sema_init()
sem_open() -
sem_close() -
sem_wait() sema_wait()
sem_trywait() sema_trywait()
sem_post() sema_post()
sem_getvalue() -
sem_unlink() -
sem_destroy() sema_destroy()
Functions Related to fork() Clean Up
POSIX (libpthread) Solaris (libthread)
pthread_atfork() -
Functions Related to Limits
POSIX (libpthread) Solaris (libthread)
pthread_once() -
Functions Related to Debugging
POSIX (libpthread) Solaris (libthread)
- thr_stksegment()
LOCKING
Synchronization
POSIX (libpthread) Solaris (libthread) Multi-
threaded behavior is asynchronous, and therefore, optimized
for concurrent and parallel processing. As threads, always
from within the same process and sometimes from multiple
processes, share global data with each other, they are not
guaranteed exclusive
access to the shared data at any point in time. Securing
mutually exclusive access to shared data requires synchron-
ization among the threads. Both POSIX and Solaris implement
four synchronization mechanisms: mutexes, condition vari-
ables, reader/writer locking (optimized frequent-read
occasional-write mutex), and semaphores.
Synchronizing multiple threads diminishes their concurrency.
The coarser the grain of synchronization, that is, the
larger the block of code that is locked, the lesser the con-
currency.
MT fork()
If a POSIX threads program calls fork(2), it implicitly
calls fork1(2), which replicates only the calling thread.
Should there be any outstanding mutexes throughout the pro-
cess, the application should call pthread_atfork(3THR), to
wait for and acquire those mutexes, prior to calling fork().
SCHEDULING
POSIX
Scheduling allocation size per thread is greater than one.
POSIX supports the following three scheduling policies:
SCHED_OTHER
Timesharing (TS) scheduling policy. It is based on the
timesharing scheduling class.
SCHED_FIFO
First-In-First-Out (FIFO) scheduling policy. Threads
scheduled to this policy, if not pre-empted by a
higher priority, will proceed until completion.
Threads whose contention scope is system
(PTHREAD_SCOPE_SYSTEM) are in real-time (RT)
scheduling class. The calling process must have a
effective user ID of 0. SCHED_FIFO for threads whose
contention scope's process (PTHREAD_SCOPE_PROCESS) is
based on the TS scheduling class.
SCHED_RR
Round-Robin scheduling policy. Threads scheduled to
this policy, if not pre-empted by a higher priority,
will execute for a time period determined by the sys-
tem. Threads whose contention scope is system
(PTHREAD_SCOPE_SYSTEM) are in real-time (RT) schedul-
ing class and the calling process must have a effec-
tive user ID of 0. SCHED_RR for threads whose conten-
tion scope is process (PTHREAD_SCOPE_PROCESS) is based
on the TS scheduling class.
Solaris
Only scheduling policy supported is SCHED_OTHER, which is
timesharing, based on the TS scheduling class.
ALTERNATE IMPLEMENTATION
The standard threads implementation is a two-level model in
which user-level threads are multiplexed over possibly fewer
lightweight processes, or LWPs. An LWP is the fundamental
unit of execution that is dispatched to a processor by the
operating system.
The system provides an alternate threads implementation, a
one-level model, in which user-level threads are associated
one-to-one with LWPs. This implementation is simpler than
the standard implementation and may be beneficial to some
multithreaded applications. It provides exactly the same
interfaces, both for POSIX threads and Solaris threads, as
the standard implementation.
To link with the alternate implementation, use the following
runpath (-R) options when linking the program:
POSIX
cc -mt ... -lpthread ... -R /usr/lib/lwp (32-bit)
cc -mt ... -lpthread ... -R /usr/lib/lwp/64 (64-bit)
Solaris
cc -mt ... -R /usr/lib/lwp (32-bit)
cc -mt ... -R /usr/lib/lwp/64 (64-bit)
For multithreaded programs that have been previously linked
with the standard threads library, the environment variables
LD_LIBRARY_PATH and LD_LIBRARY_PATH_64 can be set as follows
to bind the program at runtime to the alternate threads
library:
LD_LIBRARY_PATH=/usr/lib/lwp
LD_LIBRARY_PATH_64=/usr/lib/lwp/64
Note that if an LD_LIBRARY_PATH environment variable is in
effect for a secure process, then only the trusted direc-
tories specified by this variable will be used to augment
the runtime linker's search rules.
The runtime linker may also be instructed to use this lib-
thread by establishing an alternative object cache; see
crle(1) with the -a option.
When using the alternate one-level threads implementation,
be aware that it may create more LWPs than the standard
implementation using unbound threads. LWPs consume operat-
ing system memory in contrast to threads, which consume only
user-level memory. Thus a multithreaded application linked
against this library that creates thousands of threads would
create an equal number of LWPs and might run the system out
of resources required to support the application.
ERRORS
In a multi-threaded application, linked with libpthread or
libthread, EINTR may be returned whenever another thread
calls fork(2), which calls fork1(2) instead.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| MT-Level | MT-Safe, Fork 1-Safe |
|_____________________________|_____________________________|
FILES
POSIX
/usr/include/pthread.h /lib/libpthread.* /lib/libposix4.*
Solaris
/usr/include/thread.h /usr/include/sched.h /lib/libthread.*
SEE ALSO
crle(1), fork(2), pthread_atfork(3THR),
pthread_create(3THR), attributes(5), standards(5)
Linker and Libraries Guide
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