TMVars

A TMVar is a synchronising variable, used for communication between concurrent threads. It can be thought of as a box, which may be empty or full.

Create a TMVar which contains the supplied value.

Create a TMVar which is initially empty.

IO version of newTMVar . This is useful for creating top-level TMVar s using unsafePerformIO , because using atomically inside unsafePerformIO isn't possible.

IO version of newEmptyTMVar . This is useful for creating top-level TMVar s using unsafePerformIO , because using atomically inside unsafePerformIO isn't possible.

Return the contents of the TMVar . If the TMVar is currently empty, the transaction will retry . After a takeTMVar , the TMVar is left empty.

Put a value into a TMVar . If the TMVar is currently full, putTMVar will retry .

This is a combination of takeTMVar and putTMVar ; ie. it takes the value from the TMVar , puts it back, and also returns it.

A version of readTMVar which does not retry. Instead it returns Nothing if no value is available.

Since: 2.3

Swap the contents of a TMVar for a new value.

A version of takeTMVar that does not retry . The tryTakeTMVar function returns Nothing if the TMVar was empty, or Just a if the TMVar was full with contents a . After tryTakeTMVar , the TMVar is left empty.

A version of putTMVar that does not retry . The tryPutTMVar function attempts to put the value a into the TMVar , returning True if it was successful, or False otherwise.

Check whether a given TMVar is empty.

Make a Weak pointer to a TMVar , using the second argument as a finalizer to run when the TMVar is garbage-collected.

Since: 2.4.4