On Monday, 3 July 2000 at 9:28:34 -0600, Chuck Paterson wrote:

I'm not sure we're talking about the same thing, but if so I must be missing something. If I'm waiting on a mutex, I still need to reacquire it on wakeup, don't I? In that case, only the first process to be scheduled will actually get the mutex, and the others will block again.

So we get a creeping herd? If we wake more processes than we can handle, we're just going to spend time putting the rest to sleep again.

Fine, but there are exceptions. Obviously if we only ever have one thread waiting on the mutex, we don't have any basis for discussion.

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In my experience, I've seen mutexes used for long-term waits, and I don't see any a priori reason not to do so. Of course, if we make design decisions based on the assumption that all waits will be short, then we will have a reason, but it won't be a good one.

Before you say that long-term waits are evil, note that we're probably talking about different kinds of waits. Obviously anything that threatens to keep the system idle while it waits is bad, but a replacement for tsleep(), say, can justifiably wait for a long time.