threads(5) (man pages section 5: Standards, Environments, and Macros)

man pages section 5: Standards, Environments, and Macros

threads(5)

Name

threads, pthreads– POSIX pthreads and Solaris threads concepts

Synopsis

POSIX

cc –mt [ flag... ] file... [ -lrt 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 within libc(3LIB). Both implementations are interoperable, their functionality similar, and can be used within the same application. 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 POSIX and Solaris threading functions have counterparts with each other. POSIX function names, with the exception of the semaphore names, have a “pthread” prefix. Function names for similar POSIX and Solaris functions 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:

POSIX threads are more portable.
POSIX threads establish characteristics for each thread according to configurable attribute objects.
POSIX pthreads implement thread cancellation.
POSIX pthreads enforce scheduling algorithms.
POSIX pthreads allow for clean-up handlers for fork(2) calls.
Solaris threads can be suspended and continued.
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 available either in POSIX pthreads or Solaris threads, a hyphen (–) appears in the column.

Functions Related to Creation

`POSIX`	`Solaris`
`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`	`Solaris`
`pthread_exit()`	`thr_exit()`
`pthread_join()`	`thr_join()`
`pthread_detach()`	`–`

Functions Related to Thread Specific Data

`POSIX`	`Solaris`
`pthread_key_create()`	`thr_keycreate()`
`pthread_setspecific()`	`thr_setspecific()`
`pthread_getspecific()`	`thr_getspecific()`
`pthread_key_delete()`	`–`

Functions Related to Signals

`POSIX`	`Solaris`
`pthread_sigmask()`	`thr_sigsetmask()`
`pthread_kill()`	`thr_kill()`

Functions Related to IDs

`POSIX`	`Solaris`
`pthread_self()`	`thr_self()`
`pthread_equal()`	`–`
`–`	`thr_main()`

Functions Related to Scheduling

`POSIX`	`Solaris`
`–`	`thr_yield()`
`–`	`thr_suspend()`
`–`	`thr_continue()`
`pthread_setconcurrency()`	`thr_setconcurrency()`
`pthread_getconcurrency()`	`thr_getconcurrency()`
`pthread_setschedparam()`	`thr_setprio()`
`pthread_setschedprio()`	`thr_setprio()`
`pthread_getschedparam()`	`thr_getprio()`

Functions Related to Cancellation

`POSIX`	`Solaris`
`pthread_cancel()`	`–`
`pthread_setcancelstate()`	`–`
`pthread_setcanceltype()`	`–`
`pthread_testcancel()`	`–`
`pthread_cleanup_pop()`	`–`
`pthread_cleanup_push()`	`–`

Functions Related to Mutexes

`POSIX`	`Solaris`
`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_setrobust()`	`–`
`pthread_mutexattr_getrobust()`	`–`
`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`	`Solaris`
`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`	`Solaris`
`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`	`Solaris`
`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`	`Solaris`
`pthread_atfork()`	`–`

Functions Related to Limits

`POSIX`	`Solaris`
`pthread_once()`	`–`

Functions Related to Debugging

`POSIX`	`Solaris`
`–`	`thr_stksegment()`

Locking

Synchronization

Multithreaded 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 synchronization among the threads. Both POSIX and Solaris implement four synchronization mechanisms: mutexes, condition variables, 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 concurrency.

MT `fork()`

If a threads program calls fork(2), it implicitly calls fork1(2), which replicates only the calling thread. Should there be any outstanding mutexes throughout the process, the application should call pthread_atfork(3C) to wait for and acquire those mutexes prior to calling fork().

SCHEDULING

POSIX Threads

Solaris supports the following three POSIX scheduling policies:

SCHED_OTHER: Traditional Timesharing scheduling policy. It is based on the timesharing (TS) scheduling class.
SCHED_FIFO: First-In-First-Out scheduling policy. Threads scheduled to this policy, if not preempted by a higher priority, will proceed until completion. Such threads are in real-time (RT) scheduling class. The calling process must have a effective user ID of 0.
SCHED_RR: Round-Robin scheduling policy. Threads scheduled to this policy, if not preempted by a higher priority, will execute for a time period determined by the system. Such threads are in real-time (RT) scheduling class and the calling process must have a effective user ID of 0.

In addition to the POSIX-specified scheduling policies above, Solaris also supports these scheduling policies:

SCHED_IA: Threads are scheduled according to the Inter-Active Class (IA) policy as described in priocntl(2).
SCHED_FSS: Threads are scheduled according to the Fair-Share Class (FSS) policy as described in priocntl(2).
SCHED_FX: Threads are scheduled according to the Fixed-Priority Class (FX) policy as described in priocntl(2).

Solaris Threads

Only scheduling policy supported is SCHED_OTHER, which is timesharing, based on the TS scheduling class.

Errors

In a multithreaded application, EINTR can be returned from blocking system calls when another thread calls forkall(2).

Usage

`-mt` compiler option

The -mt compiler option compiles and links for multithreaded code. It compiles source files with -D_REENTRANT and augments the set of support libraries properly.

Attributes

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
MT-Level	MT-Safe, Fork 1-Safe