On Wed, 4 Aug 2010 17:06:59 +0300 Antti Kantee <po...@cs.hut.fi> wrote: > Never realized file descriptors and threads were so tricky ;)
I'm just finishing writing multi-threaded logging subsystem for one of my projects. I think I faced a similar issue with threads and shared file descriptors. Threads can log data to the same file, or different files on the filesystem. They can log data to one file, or many different files simultaneously. I implemented a new type, which is basically a structure that contains mutex, file descriptor, file path string and reference counter. Any thread doing I/O on a particular descriptor has to lock its mutex. Since, logging data can remain in buffers, waiting to be flushed, threads increment descriptors' reference counters, when they flush buffers they decrement those counters. This ensures that descriptors are not freed from memory, until reference counter drops to 0. If the value of the descriptor == -1, thread holding the lock calls open() with the file path as the first argument. My code uses a hash table to lookup descriptors, however I don't use the value of an open file descriptor (which can change between multiple open()/close() calls), but the address of the structure that describes a particular file descriptor.
