Tomasz Kojm wrote:There _are_ current issues with thread-based clamd (and thread-based software in general, as everything (memory, fd's etc)is shared between threads:
The current CVS code contains a new directive: UseProcesses that will cause clamd to use processes instead of threads. Initial version but seems to work ;) It should be really useful for clamav-milter users.
What are the advantages of processes vs. threads in this case? Doesn't the creation of processes use more ressources?
Thanks for clarification.
- Marc
- some users (especially milter users) report clamd "freezing", effectively stopping mail queueing
- resource cleanup in clamd is not optimal (especially on internal failures, where fd's are not closed and some memory is not free()'d)
Cons:
- On some architectures, fork()/exec() are a lot slower than pthread_create() (Solaris comes to mind)
- lightly increased resource usage on "modern" systems where forked processes share memory until one process writes to it (copy-on-write), and greatly incresed resource usage where such feature is not provided
Pros:
- Every clamd subprocess can directly exit() on failure; all resources are automatically free()d and fd's are closed.
- No need for mutexes to keep track of writes to memory areas shared by all threads (think of 3rd party libraries that may be not thread save, even in some small areas only)
- one mad-running thread can't take the hole process down
I think it's a great leap toward real production quality for clamd. A big Thank You to Tomasz for making that feature available in the main trunk (for those who didn't know: a patch for that did already exist, but it was either "run CVS versin with threads", or "run patched version with fork/exec" AFAIR).
Again, Thanks!
Thomas
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