On 7/5/07, Donald Bruce Stewart
Yep. The current impl is:
mmapFile :: FilePath -> IO ByteString mmapFile f = mmap f >>= \(fp,l) -> return $! PS fp 0 l
mmap :: FilePath -> IO (ForeignPtr Word8, Int) mmap = do ... p <- mmap l fd fp <- newForeignPtr p unmap -- attach unmap finaliser return fp
Which, if I read it correctly is not safe in a concurrent/multitasking environment, since it wraps the underlying mmapped region. In many programs, I'm sure this won't be a problem. Unfortunately, the system I'm working on is multi-threaded, and we definitely want to update regions. Perhaps I'll have to bite the bullet and implement the Mapping thing I described. The really unfortunate thing is that I'd really like to be able to do it within the STM monad, with rollback, etc - escaping to the IO monad is annoying. FWIW, the technique I use to handle this kind of situation may be of general interest. Consider a cache of structures reconstituted from an external file. If a requested item is not in the cache, then we throw an exception which is caught in a wrapper function which is in the IO monad, read the requested structure, stick it in the cache, then rerun the transaction. There are a few details you have to get right, including making sure none of the items you require to complete the operation get evicted by another thread, but it works very nicely. T. -- Dr Thomas Conway drtomc@gmail.com Silence is the perfectest herald of joy: I were but little happy, if I could say how much.