On 2008 Nov 10, at 16:29, Jason Dusek wrote:
I've put together a simple test case for a rather annoying problem. I've got a program that drives other programs. For example, it can drive `cat`:
:; Simple cat a-file
When the file is a little bit greater than 135060 bytes, this program fails to produce any output at all -- I need to use ^C to get my console back.
If you are feeding it input and collecting output, you need to forkIO one or both. In particular, the sequence feed input read output waitForProcess will deadlock if at any point the input or output pipe fills: one side will be blocked on write() waiting for the other side to read() from the pipe, while the read() side is blocked waiting for write() on the other pipe, which won't be read() because that's the first side. (There are other variants of this, but that's the general form: processes blocked each waiting for the other side to do something.)
If I remove the `hClose`, the example program just hangs, no matter the size of the input.
That's another symptom of it, yes, made worse because the pipe close is now implicit and the other side won't stop read()ing until the pipe is close()d by the first side.
simple exe bytes args = do (i, o, e, p) <- runInteractiveProcess exe args Nothing Nothing hPut i bytes s <- hGetContents o hClose i return s
Yep, that's your problem. forkIO the hPut. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH