GHC.IOPort

An IOPort is a synchronising variable, used for communication between concurrent threads, where one of the threads is controlled by an external state. e.g. by an I/O action that is serviced by the runtime. It can be thought of as a box, which may be empty or full.

It is mostly similar to the behavior of Control.Concurrent.MVar.MVar except writeIOPort doesn't block if the variable is full and the GC won't forcibly release the lock if it thinks there's a deadlock.

The properties of IOPorts are: * Writing to an empty IOPort will not block. * Writing to an full IOPort will not block. It might throw an exception. * Reading from an IOPort for the second time might throw an exception. * Reading from a full IOPort will not block, return the value and empty the port. * Reading from an empty IOPort will block until a write. * Reusing an IOPort (that is, reading or writing twice) is not supported and might throw an exception. Even if reads and writes are interleaved.

This type is very much GHC internal. It might be changed or removed without notice in future releases.

Create an IOPort which contains the supplied value.

Create an IOPort which is initially empty.

Atomically read the contents of the IOPort. If the IOPort is currently empty, readIOPort will wait until it is full. After a readIOPort, the IOPort is left empty.

There is one important property of readIOPort:

• Only a single threads can be blocked on an IOPort.

Put a value into an IOPort. If the IOPort is currently full, writeIOPort will throw an exception.

There is one important property of writeIOPort:

• Only a single thread can be blocked on an IOPort.