Anonymous pipe
Encyclopedia
In computer science
, an anonymous pipe is a simplex FIFO
communication channel that may be used for one-way interprocess communication (IPC). An implementation is often integrated into the operating system
's file IO
subsystem. Typically a parent program opens anonymous pipes, and creates a new process that inherits the other ends of the pipes, or creates several new processes and arranges them in a pipeline
.
Full-duplex (two-way) communication normally requires two anonymous pipes.
are an important part of many Unix
applications and support for them is well integrated into most Unix-like
operating systems. Pipes are created using the
, which creates a new pipe and returns a pair of file descriptor
s referring to the read and write ends of the pipe. In a Unix shell
a pipeline
is created using the "|" character and many Unix programs are designed as filters
to work with pipes.
, anonymous pipes are created and configured with API functions that are specific to the IO facility. In this case
On Microsoft Windows, reads and writes to anonymous pipes are always blocking. In other words, a read from an empty pipe will cause the calling thread to wait until at least one byte becomes available or an end-of-file
is received as a result of the write handle of the pipe being closed. Likewise, a write to a full pipe will cause the calling thread to wait until space becomes available to store the data being written. Reads may return with fewer than the number of bytes requested (also called a short read).
New processes can inherit handles to anonymous pipes in the creation process.
Computer science
Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...
, an anonymous pipe is a simplex FIFO
FIFO
FIFO is an acronym for First In, First Out, an abstraction related to ways of organizing and manipulation of data relative to time and prioritization...
communication channel that may be used for one-way interprocess communication (IPC). An implementation is often integrated into the operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
's file IO
Input/output
In computing, input/output, or I/O, refers to the communication between an information processing system , and the outside world, possibly a human, or another information processing system. Inputs are the signals or data received by the system, and outputs are the signals or data sent from it...
subsystem. Typically a parent program opens anonymous pipes, and creates a new process that inherits the other ends of the pipes, or creates several new processes and arranges them in a pipeline
Pipeline (software)
In software engineering, a pipeline consists of a chain of processing elements , arranged so that the output of each element is the input of the next. Usually some amount of buffering is provided between consecutive elements...
.
Full-duplex (two-way) communication normally requires two anonymous pipes.
Unix
PipelinesPipeline (Unix)
In Unix-like computer operating systems , a pipeline is the original software pipeline: a set of processes chained by their standard streams, so that the output of each process feeds directly as input to the next one. Each connection is implemented by an anonymous pipe...
are an important part of many Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
applications and support for them is well integrated into most Unix-like
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
operating systems. Pipes are created using the
pipe system callSystem call
In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services , creating and executing new processes, and communicating with integral kernel services...
, which creates a new pipe and returns a pair of file descriptor
File descriptor
In computer programming, a file descriptor is an abstract indicator for accessing a file. The term is generally used in POSIX operating systems...
s referring to the read and write ends of the pipe. In a Unix shell
Unix shell
A Unix shell is a command-line interpreter or shell that provides a traditional user interface for the Unix operating system and for Unix-like systems...
a pipeline
Pipeline (Unix)
In Unix-like computer operating systems , a pipeline is the original software pipeline: a set of processes chained by their standard streams, so that the output of each process feeds directly as input to the next one. Each connection is implemented by an anonymous pipe...
is created using the "|" character and many Unix programs are designed as filters
Filter (Unix)
In Unix and Unix-like operating systems, a filter is a program that gets most of its data from its standard input and writes its main results to its standard output . Unix filters are often used as elements of pipelines...
to work with pipes.
Microsoft Windows
Like many other device IO and IPC facilities in the Windows APIWindows API
The Windows API, informally WinAPI, is Microsoft's core set of application programming interfaces available in the Microsoft Windows operating systems. It was formerly called the Win32 API; however, the name "Windows API" more accurately reflects its roots in 16-bit Windows and its support on...
, anonymous pipes are created and configured with API functions that are specific to the IO facility. In this case
CreatePipe is used to create an anonymous pipe with separate handles for the read and write ends of the pipe. Read and write IO operations on the pipe are performed with the standard IO facility API functions ReadFile and WriteFile.On Microsoft Windows, reads and writes to anonymous pipes are always blocking. In other words, a read from an empty pipe will cause the calling thread to wait until at least one byte becomes available or an end-of-file
End-of-file
In computing, end of file is a condition in a computer operating system where no more data can be read from a data source...
is received as a result of the write handle of the pipe being closed. Likewise, a write to a full pipe will cause the calling thread to wait until space becomes available to store the data being written. Reads may return with fewer than the number of bytes requested (also called a short read).
New processes can inherit handles to anonymous pipes in the creation process.