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Sistemi operativi - Syscall pthread_cond_wait Appunti scolastici Premium

Appunti di sistemi operativi per l'esame dei professori Cotroneo e Natella. gli argomenti trattati sono i seguenti: System call pthread_cond_wait: name, sypnosis, description, return value, errors, examples, application usage, future directions, see also, derivation.

Esame di Sistemi operativi docente Prof. D. Cotroneo

Anteprima

ESTRATTO DOCUMENTO

pthread_cond_wait http://www.opengroup.org/onlinepubs/007908799/xsh/pthread_cond_t...

The Single UNIX ® Specification, Version 2

Copyright © 1997 The Open Group

NAME

pthread_cond_wait, pthread_cond_timedwait - wait on a condition

SYNOPSIS

#include <pthread.h>

int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);

int pthread_cond_timedwait(pthread_cond_t *cond,

pthread_mutex_t *mutex, const struct timespec *abstime);

DESCRIPTION

The pthread_cond_wait() and pthread_cond_timedwait() functions are used to block on a

condition variable. They are called with mutex locked by the calling thread or undefined

behaviour will result.

These functions atomically release mutex and cause the calling thread to block on the

condition variable cond; atomically here means "atomically with respect to access by another

thread to the mutex and then the condition variable". That is, if another thread is able to

acquire the mutex after the about-to-block thread has released it, then a subsequent call to

pthread_cond_signal() or pthread_cond_broadcast() in that thread behaves as if it were

issued after the about-to-block thread has blocked.

Upon successful return, the mutex has been locked and is owned by the calling thread.

When using condition variables there is always a boolean predicate involving shared variables

associated with each condition wait that is true if the thread should proceed. Spurious

wakeups from the pthread_cond_wait() or pthread_cond_timedwait() functions may occur.

Since the return from pthread_cond_wait() or pthread_cond_timedwait() does not imply

anything about the value of this predicate, the predicate should be re-evaluated upon such

return.

The effect of using more than one mutex for concurrent pthread_cond_wait() or

pthread_cond_timedwait() operations on the same condition variable is undefined; that is, a

condition variable becomes bound to a unique mutex when a thread waits on the condition

variable, and this (dynamic) binding ends when the wait returns.

A condition wait (whether timed or not) is a cancellation point. When the cancelability enable

state of a thread is set to PTHREAD_CANCEL_DEFERRED, a side effect of acting upon a

cancellation request while in a condition wait is that the mutex is (in effect) re-acquired

before calling the first cancellation cleanup handler. The effect is as if the thread were

unblocked, allowed to execute up to the point of returning from the call to

pthread_cond_wait() or pthread_cond_timedwait(), but at that point notices the cancellation

request and instead of returning to the caller of pthread_cond_wait() or

pthread_cond_timedwait(), starts the thread cancellation activities, which includes calling

cancellation cleanup handlers.

A thread that has been unblocked because it has been canceled while blocked in a call to

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DETTAGLI
Corso di laurea: Corso di laurea in ingegneria informatica
SSD:
A.A.: 2013-2014

I contenuti di questa pagina costituiscono rielaborazioni personali del Publisher N. A. di informazioni apprese con la frequenza delle lezioni di Sistemi operativi e studio autonomo di eventuali libri di riferimento in preparazione dell'esame finale o della tesi. Non devono intendersi come materiale ufficiale dell'università Napoli Federico II - Unina o del prof Cotroneo Domenico.

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