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In the Solaris implementation of condition variables, a spurious wakeup may occur without the condition being assigned if the process is signaled; the wait system call aborts and returns EINTR. [2] The Linux p-thread implementation of condition variables guarantees that it will not do that. [3] [4]
// Call signal or broadcast, depending on which condition variables' // predicates (who share mutex m) have been made true or may have been made true, // and the monitor semantic type being used. for (cv_x in cvs_to_signal) {signal (cv_x); // Or: broadcast(cv_x);} // One or more threads have been woken up but will block as soon as they try ...
In computer operating systems, a process (or task) may wait for another process to complete its execution. In most systems, a parent process can create an independently executing child process . The parent process may then issue a wait system call , which suspends the execution of the parent process while the child executes.
In particular, the POSIX specification and the Linux man page signal (7) require that all system functions directly or indirectly called from a signal function are async-signal safe. [6] [7] The signal-safety(7) man page gives a list of such async-signal safe system functions (practically the system calls), otherwise it is an undefined behavior ...
In computing, a futex (short for "fast userspace mutex") is a kernel system call that programmers can use to implement basic locking, or as a building block for higher-level locking abstractions such as semaphores and POSIX mutexes or condition variables. A futex consists of a kernel-space wait queue that is attached to an atomic integer in ...
wait normally returns the exit status of the last job which terminated. It may also return 127 in the event that n specifies a non-existent job or zero if there were no jobs to wait for. Because wait needs to be aware of the job table of the current shell execution environment, it is usually implemented as a shell builtin .
In Unix and other POSIX-compatible systems, the parent process can retrieve the exit status of a child process using the wait() family of system calls defined in wait.h. [10] Of these, the waitid() [11] call retrieves the full exit status, but the older wait() and waitpid() [12] calls retrieve only the least significant 8 bits of the exit status.
When the child process terminates ("dies"), either normally by calling exit, or abnormally due to a fatal exception or signal (e.g., SIGTERM, SIGINT, SIGKILL), an exit status is returned to the operating system and a SIGCHLD signal is sent to the parent process. The exit status can then be retrieved by the parent process via the wait system call.