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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]
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 most types of monitors, these other threads may signal the condition variable c to indicate that assertion P c is true in the current state. Thus there are three main operations on condition variables: wait c, m, where c is a condition variable and m is a mutex (lock) associated with the monitor.
In ALGOL 68, the Linux kernel, [11] and in some English textbooks, the V and P operations are called, respectively, up and down. In software engineering practice, they are often called signal and wait, [12] release and acquire [12] (standard Java library), [13] or post and pend. Some texts call them vacate and procure to match the original ...
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.
Signals are received in signal handlers, small, limited pieces of code that run while the rest of the task is suspended; if a signal is received and handled while the task is blocking in select(), select will return early with EINTR; if a signal is received while the task is CPU bound, the task will be suspended between instructions until the ...
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.
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.