DB_THREAD support in Berkeley DB/glibc

[David Edelsohn]

>>>>> Geoff Keating writes:

Geoff> We don't need 'isync', 'sync' will do just fine, and is faster.  We
Geoff> are only concerned here with memory coherency.  In fact, 'isync' does
Geoff> not imply 'sync' in a multiprocessor implementation; 'sync' does an
Geoff> extra broadcast on the bus.  The PowerPC User's Manual says

Geoff> The sync instruction can be used to ensure that the result of all
Geoff> stores into a data structure, performed in a "critical section" of a
Geoff> program, are seen by other processors before the data structure is
Geoff> seen as unlocked.

Geoff> We probably want 'sync' before and after, although it's probable the
Geoff> 'after' is unnecessary.

	"sync" is not faster; sync is a full context synchronization
instruction.  As I had mentioned to David, the necessity of a sync *after*
the store depends on the semantics of this programming model.  Maybe in
this context one should sync before acquiring the lock and then sync after
releasing the lock.

David

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