System.IO.Unsafe.Compat

base-compat-0.12.1: A compatibility layer for base

Safe Haskell | Safe-Inferred
Language | Haskell2010

System.IO.Unsafe.Compat

Synopsis

- module System.IO.Unsafe
- unsafeFixIO :: (a -> IO a) -> IO a
- unsafeDupablePerformIO :: IO a -> a

# Documentation

module System.IO.Unsafe

unsafeFixIO :: (a -> IO a) -> IO a #

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

unsafeDupablePerformIO :: IO a -> a #

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