Documentation

A slightly faster version of fixIO that may not be safe to use with multiple threads. The unsafety arises when used like this:

 unsafeFixIO $ \r -> do
    forkIO (print r)
    return (...)

In this case, the child thread will receive a NonTermination exception instead of waiting for the value of r to be computed.

Since: base-4.5.0.0

This version of unsafePerformIO is more efficient because it omits the check that the IO is only being performed by a single thread. Hence, when you use unsafeDupablePerformIO, there is a possibility that the IO action may be performed multiple times (on a multiprocessor), and you should therefore ensure that it gives the same results each time. It may even happen that one of the duplicated IO actions is only run partially, and then interrupted in the middle without an exception being raised. Therefore, functions like bracket cannot be used safely within unsafeDupablePerformIO.

Since: base-4.4.0.0