On 1 Apr '08, at 4:53 PM, Martin Redington wrote:
You'd kind of hope that NSTask would clean up in its dealloc method, but apparently not.
But you're not (and shouldn't be) calling -dealloc, you're calling - release. My guess is that the NSTask retains itself while the process is running, so as not to leave anything dangling, then releases itself when it exits. If you don't wait for the task to exit, but start lots of others as fast as you can, you're probably piling up lots of tasks at once. Collect about 84, and suddenly you can't start any more.
Jim - any particular reason why you'd not use NSTask?I guess I'm paying the fork/exec overhead, and some interprocess piping and (a very small bit of) extra I/O for each NSTask.
It's vastly slower to do this by forking a process.NSTask can be annoying to deal with (I've had trouble getting it to cooperate, and you're running into problems too.) It's more code than simply calling CommonDigest, and it's less clear to the reader what's going on.
I will actually be caching a lot of the output, so I expect the numbers to be much smaller on subsequent scans, although even once off, 3,000 spawns does seem a bit gratuitous. Performance was much better than I expected though - about 12 minutes for the md5 phase.
That's 0.25 seconds per file. I think you can do better than that, unless the files are really big.
Also, you're aware that MD5 shouldn't be used for anything security- related anymore? Last I heard it's pretty close to being fully broken. SHA-1 is a lot more secure, and has a larger output which itself makes collisions less likely.
—Jens
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