System.Process.CommunicationHandle.Internal

CommunicationHandle: a Handle that can be serialised,

newtype CommunicationHandle

A CommunicationHandle is an abstraction over operating-system specific internal representation of a Handle, which can be communicated through a command-line interface.

In a typical use case, the parent process creates a pipe, using e.g. createWeReadTheyWritePipe or createTheyReadWeWritePipe.

• One end of the pipe is a Handle, which can be read from/written to by the parent process.
• The other end is a CommunicationHandle, which can be inherited by a child process. A reference to the handle can be serialised (using the Show instance), and passed to the child process. It is recommended to close the parent's reference to the CommunicationHandle using closeCommunicationHandle after it has been inherited by the child process.
• The child process can deserialise the CommunicationHandle (using the Read instance), and then use openCommunicationHandleWrite or openCommunicationHandleRead in order to retrieve a Handle which it can write to/read from.

readCreateProcessWithExitCodeCommunicationHandle provides a high-level API to this functionality. See there for example code.

Since: 1.6.20.0

Constructors

CommunicationHandle Fd

Instances

Read CommunicationHandle

Defined in System.Process.CommunicationHandle.Internal

Methods

readsPrec :: Int -> ReadS CommunicationHandle

readList :: ReadS [CommunicationHandle]

readPrec :: ReadPrec CommunicationHandle

readListPrec :: ReadPrec [CommunicationHandle]

Show CommunicationHandle

Defined in System.Process.CommunicationHandle.Internal

Methods

showsPrec :: Int -> CommunicationHandle -> ShowS

show :: CommunicationHandle -> String

showList :: [CommunicationHandle] -> ShowS

Eq CommunicationHandle

Defined in System.Process.CommunicationHandle.Internal

Methods

(==) :: CommunicationHandle -> CommunicationHandle -> Bool

(/=) :: CommunicationHandle -> CommunicationHandle -> Bool

Ord CommunicationHandle

Defined in System.Process.CommunicationHandle.Internal

Methods

compare :: CommunicationHandle -> CommunicationHandle -> Ordering

(<) :: CommunicationHandle -> CommunicationHandle -> Bool

(<=) :: CommunicationHandle -> CommunicationHandle -> Bool

(>) :: CommunicationHandle -> CommunicationHandle -> Bool

(>=) :: CommunicationHandle -> CommunicationHandle -> Bool

max :: CommunicationHandle -> CommunicationHandle -> CommunicationHandle

min :: CommunicationHandle -> CommunicationHandle -> CommunicationHandle

closeCommunicationHandle :: CommunicationHandle -> IO ()

Close a CommunicationHandle.

Use this to close the CommunicationHandle in the parent process after the CommunicationHandle has been inherited by the child process.

Since: 1.6.20.0

Internal functions

useCommunicationHandle :: Bool -> CommunicationHandle -> IO Handle

Internal function used to define openCommunicationHandleRead and openCommunicationHandleWrite.

createCommunicationPipe

Arguments

:: (forall a. (a, a) -> (a, a))

id (we read, they write) or swap (they read, we write)

-> Bool

whether to pass a handle supporting asynchronous I/O to the child process (this flag only has an effect on Windows and when using WinIO)

-> IO (Handle, CommunicationHandle)

Internal helper function used to define createWeReadTheyWritePipe and createTheyReadWeWritePipe while reducing code duplication.

The returned Handle does not have any finalizers attached to it; use hClose to close it.