The do ... while loop in our wait code could spin while waiting
because the event object wasn't reset until there were no longer any
events waiting to be woken up. We also want to reset the event object
if the count of events to wake up reaches zero.
Found by Chris Davis. Fixes bug 3053358.
The interface from the user's POV is similar to the locking
implementation: either provide a structure full of function
pointers, or just call evthread_use_*_threads() and everything will
be okay.
The internal interface is meant to vaguely resemble pthread_cond_*,
which Windows people will better recognize as *ConditionVariable*.
Previously we were using InitializeCriticalSection, which creates a
lock that blocks immediately on contention and waits to be
rescheduled. This is inefficient; it's better to wait for a little
while before telling the US to reschedule us, in case the lock becomes
available again really soon (since most locks mostly do).
Good pthreads implementations do this automatically. On Windows,
though, we need to call this magic function, and we need to pick the
spin count ourselves.
Previously, there was no good way to request different kinds of lock
(say, read/write vs writeonly or recursive vs nonrecursive), or for a
lock function to signal failure (which would be important for a
trylock mode).
This patch revises the lock API to be a bit more useful. The older
lock calls are still supported for now.
We also add a debugging mode to catch common errors in using the
locking APIs.
a) this is 2009
b) niels and nick have been comaintainers for a while
c) saying "all rights reserved" when you then go on to explicitly
disclaim some rights is sheer cargo-cultism.
svn:r1065
