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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 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 ...
sleep until the operating system kernel determines that there are no readers left using the old structure, for example, in the Linux kernel, by using synchronize_rcu(), once awakened by the kernel, deallocate the old structure. So the structure is read concurrently with a thread copying in order to do an update, hence the name "read-copy update ...
Linux also supports mandatory locking through the special -o mand parameter for file system mounting , but this is rarely used. Some Unix-like operating systems prevent attempts to open the executable file of a running program for writing; this is a third form of locking, separate from those provided by fcntl and flock .
inotify (inode notify) is a Linux kernel subsystem created by John McCutchan, which monitors changes to the filesystem, and reports those changes to applications.It can be used to automatically update directory views, reload configuration files, log changes, backup, synchronize, and upload.
In computer science and software engineering, busy-waiting, busy-looping or spinning is a technique in which a process repeatedly checks to see if a condition is true, such as whether keyboard input or a lock is available. Spinning can also be used to generate an arbitrary time delay, a technique that was necessary on systems that lacked a ...
But such an approach, called synchronous I/O or blocking I/O, would block the progress of a program while the communication is in progress, leaving system resources idle. When a program makes many I/O operations (such as a program mainly or largely dependent on user input ), this means that the processor can spend almost all of its time idle ...
Inside the loop, the server process is put to sleep while waiting to accept a client connection. [4] Upon accepting a client connection, the server then executes a read system call that will block wait. The client connects to the server's socket via the server's address. The client process then writes a message for the server process to read.