interruptible file open

Motivation

When working with FIFOs, it's sometimes desirable to using a blocking open, so that it will wait until a writer appears. base offers this in GHC.IO.Handle.FD.openFileBlocking. However, that call is not interruptible. I've made a very simple single-threaded program which is intended to blocking-open a FIFO repeatedly as its main loop, and which should shut down on ctrl+c, but in order to get this I had to hack up my own special open and read calls where the open call is marked interruptible.

Proposal

Unless it's a bad idea, set the c_safe_open foreign call to interruptible and make it deal properly with asynchronous exceptions. Otherwise, offer a new way to get an interruptible blocking open.

Status

The proposal has been implemented for Posix systems but not for Windows.