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Fast reader/writer locksFast reader/writer locksPosted Jan 30, 2003 5:16 UTC (Thu) by cpeterso (guest, #305)In reply to: Fast reader/writer locks by rickfdd Parent article: Fast reader/writer locks
I think there would be a race condition if the reader just looked for even/odd sequence number changes. If the sequence number was increments TWICE (by one or multiple writers), then the reader might not recognize the data change event.
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Fast reader/writer locks Posted Jan 30, 2003 13:43 UTC (Thu) by bastiaan (guest, #5170) [Link] I guess what Rick means is that if you use one sequence the reader will know a concurrent write is in progress if the sequence is odd, in which case it can retry without first copying the data. In code:
do {
while((seq = fr_read_seq(&some_lock)) & 1);
/* copy data */
} while (seq != fr_read_seq(&some_lock));
However, since the concurrent write is very unlikely to happen, this extra test may be not worthwhile. But I still don't see why Stephen uses two sequences instead of one.
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