Re: Wait free LW_SHARED acquisition - v0.9

On Wed, Oct 8, 2014 at 9:35 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> 2) Implement the wait free LW_SHARED algorithm.

+ * too high for workloads/locks that were locked in shared mode very

s/locked/taken/?

+ * frequently. Often we were spinning in the (obviously exlusive) spinlock,

exclusive.

+ * acquiration for locks that aren't exclusively locked.

acquisition.

+ * For exlusive lock acquisition we use an atomic compare-and-exchange on the

exclusive.

+ * lockcount variable swapping in EXCLUSIVE_LOCK/1<<31-1/0x7FFFFFFF if and only

Add comma after variable. Find some way of describing the special
value (maybe "a sentinel value, EXCLUSIVE_LOCK") just once, instead of
three times.

+ * if the current value of lockcount is 0. If the swap was not successfull, we

successful.

+ * by 1 again. If so, we have to wait for the exlusive locker to release the

exclusive.

+ * The attentive reader probably might have noticed that naively doing the

"probably might" is redundant. Delete probably.

+ * notice that we have to wait. Unfortunately until we have finished queuing,

until -> by the time

+ * Phase 2: Add us too the waitqueue of the lock

too -> to. And maybe us -> ourselves.

+ * get queued in Phase 2 and we can wake them up if neccessary or they will

necessary.

+ * When acquiring shared locks it's possible that we disturb an exclusive
+ * waiter. If that's a problem for the specific user, pass in a valid pointer
+ * for 'potentially_spurious'. Its value will be set to true if we possibly
+ * did so. The caller then has to handle that scenario.

"disturb" is not clear enough.

+ /* yipeyyahee */

Although this will be clear to individuals with a good command of
English, I suggest avoiding such usages.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company