Messages in this thread |  | | | Date | Mon, 29 Jan 2001 18:26:33 +0100 | | From | Andi Kleen <> |
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On Mon, Jan 29, 2001 at 11:01:31AM -0600, Timur Tabi wrote: > What makes it more frustrating is that some people on this list talk as if > things things are common knowledge. I've been following this mailing list for > months, and until today I had no idea sleep_on was bad. All the documentation > I've read to date freely uses sleep_on in the sample code. In fact, I still
When Linux documentation uses sleep_on it is probably broken and should be fixed. Unix (not linux) documentation uses sleep_on commonly, but Unix has different wait queue semantics and it is usually safe there. You're probably reading the wrong documentation, e.g. Rusty's kernel hacking HOWTO describes it correctly (and a lot of the other rules)
> don't even know WHY it's bad. Not only that, but what am I supposed to use > instead?
You can miss wakeups. The standard pattern is:
get locks
add_wait_queue(&waitqueue, &wait); for (;;) { if (condition you're waiting for is true) break; unlock any non sleeping locks you need for condition __set_task_state(current, TASK_UNINTERRUPTIBLE); schedule(); __set_task_state(current, TASK_RUNNING); reaquire locks } remove_wait_queue(&waitqueue, &wait); When you want to handle signals you can check for them before or after the condition check. Also use TASK_INTERRUPTIBLE in this case.
When you need a timeout use schedule_timeout().
For some cases you can also use the wait_event_* macros which encapsulate that for you, assuming condition can be tested/used lockless.
An alternative is to use a semaphore, although that behaves a bit differently under load.
> This is what I find most frustrating about Linux. If I were a Windows driver > programmer, I could walk into any bookstore and pick up any of a dozen books > that explains everything, leaving no room for doubt.
Just why are Windows drivers so buggy then?
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