- I want to set timeouts on various IO operations in an existing
library, ftphs. However, even if I wrap every call in `block`, it's
unclear whether ftphs has been coded to deal with asynchronous
exceptions, or whether state could be rendered inconsistent. Is there
any solution for this aside from auditing/changing ftphs?
- I can't find any documentation on which calls are (either directly or
indirectly, or parametrically) "interruptible operations" (to use the
term from the Async Exceptions paper). For instance, I experimentally
determined that hPutStrLn on a socket is *not*. Does such documentation
exist anywhere? Furthermore, is there any way to embed this information
in the type system, so that Haskellers don't produce
async-exception-unaware code? (Effectively, introducing checked interrupts?)
- The above finding of hPutStrLn (as an example) is somewhat surprising,
since the socket buffer may be full, causing the call to block
indefinitely. We can unblock that call, but unless there's a way to
atomically reinstate the block and save the result of the computation
(the unit value), this effectively makes it impossible to determine
whether the hPutStrLn returned. (Admittedly, this is a contrived
example, since whether a call to hPutStrLn returns is usually not a
useful result - but this is the first thing I tried, and I'm guessing
there are more such IO operations that actually yield useful results.)
- Are there any higher-level concurrency libraries that actually tackle
these hand-in-hand issues (safe asynchronous interruptible IO,
two-phase-commit to prevent dropping results, choice, etc.)? I tried
searching for a while, coming up with PiMonad, HAppS.Util,
MissingH.Threads.Timeout, but none of them really address these issues.
Perhaps this is just impossible in Concurrent Haskell, and one would
need to resort to the sure-fire home-rolled solution using delimited
continuations and cooperative scheduling for any serious concurrency
abstractions for systems programming.
Thanks in advance for any answers!
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