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ck_epoch: Reload epoch value on scan failure.

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ck_pring
Samy Al Bahra 13 years ago
parent 7821be8a60
commit 1c4183cf44
1 changed files with 10 additions and 9 deletions
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19
src/ck_epoch.c
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@ -93,10 +93,11 @@
* critical sections started at e_g - 1 must have been completed. If * critical sections started at e_g - 1 must have been completed. If
* any epoch read-side critical sections at e_g - 1 were still active, * any epoch read-side critical sections at e_g - 1 were still active,
* then we would never increment to e_g + 1 (active != 0 ^ e != e_g). * then we would never increment to e_g + 1 (active != 0 ^ e != e_g).
* Additionally, e_g may still have hazardous references to objects logically * Additionally, e_g may still have hazardous references to objects
* deleted at e_g - 1 which means objects logically deleted at e_g - 1 cannot * logically deleted at e_g - 1 which means objects logically deleted
* be deleted at e_g + 1 (since it is valid for active threads to be at e_g or * at e_g - 1 cannot be deleted at e_g + 1 unless all threads have
* e_g + 1 and threads at e_g still require safe memory accesses). * observed e_g + 1 (since it is valid for active threads to be at e_g
* and threads at e_g still require safe memory accesses).
* *
* However, at e_g + 2, all active threads must be either at e_g + 1 or * However, at e_g + 2, all active threads must be either at e_g + 1 or
* e_g + 2. Though e_g + 2 may share hazardous references with e_g + 1, * e_g + 2. Though e_g + 2 may share hazardous references with e_g + 1,
@ -106,12 +107,10 @@
* *
* To summarize these important points, * To summarize these important points,
* 1) Active threads will always have a value of e_g or e_g - 1. * 1) Active threads will always have a value of e_g or e_g - 1.
* 2) Items that are logically deleted at e_g or e_g - 1 cannot be * 2) Items that are logically deleted e_g or e_g - 1 cannot be
* physically deleted. * physically deleted.
* 3) Objects logically deleted at e_g - 1 can be physically destroyed * 3) Objects logically deleted at e_g - 1 can be physically destroyed
* at e_g + 2. In other words, for any current value of the global epoch * at e_g + 2 or at e_g + 1 if no threads are at e_g.
* counter e_g, objects logically deleted at e_g can be physically
* deleted at e_g + 3.
* *
* Last but not least, if we are at e_g + 2, then no active thread is at * Last but not least, if we are at e_g + 2, then no active thread is at
* e_g which means it is safe to apply modulo-3 arithmetic to e_g value * e_g which means it is safe to apply modulo-3 arithmetic to e_g value
@ -302,8 +301,10 @@ ck_epoch_barrier(struct ck_epoch *global, struct ck_epoch_record *record)
* Determine whether all threads have observed the current epoch. * Determine whether all threads have observed the current epoch.
* We can get away without a fence here. * We can get away without a fence here.
*/ */
while (cr = ck_epoch_scan(global, cr, delta, &active), cr != NULL) while (cr = ck_epoch_scan(global, cr, delta, &active), cr != NULL) {
ck_pr_stall(); ck_pr_stall();
delta = ck_pr_load_uint(&global->epoch);
}
/* /*
* If we have observed all threads as inactive, then we assume * If we have observed all threads as inactive, then we assume

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