Function ck_epoch_synchronize_wait

freebsd/contrib/ck/src/ck_epoch.c:424–526

* This function must not be called with-in read section. */

 * This function must not be called with-in read section.
 */
void
ck_epoch_synchronize_wait(struct ck_epoch *global,
    ck_epoch_wait_cb_t *cb, void *ct)
{
	struct ck_epoch_record *cr;
	unsigned int delta, epoch, goal, i;
	bool active;

	ck_pr_fence_memory();

	/*
	 * The observation of the global epoch must be ordered with respect to
	 * all prior operations. The re-ordering of loads is permitted given
	 * monoticity of global epoch counter.
	 *
	 * If UINT_MAX concurrent mutations were to occur then it is possible
	 * to encounter an ABA-issue. If this is a concern, consider tuning
	 * write-side concurrency.
	 */
	delta = epoch = ck_pr_load_uint(&global->epoch);
	goal = epoch + CK_EPOCH_GRACE;

	for (i = 0, cr = NULL; i < CK_EPOCH_GRACE - 1; cr = NULL, i++) {
		bool r;

		/*
		 * Determine whether all threads have observed the current
		 * epoch with respect to the updates on invocation.
		 */
		while (cr = ck_epoch_scan(global, cr, delta, &active),
		    cr != NULL) {
			unsigned int e_d;

			ck_pr_stall();

			/*
			 * Another writer may have already observed a grace
			 * period.
			 */
			e_d = ck_pr_load_uint(&global->epoch);
			if (e_d == delta) {
				epoch_block(global, cr, cb, ct);
				continue;
			}

			/*
			 * If the epoch has been updated, we may have already
			 * met our goal.
			 */
			delta = e_d;
			if ((goal > epoch) & (delta >= goal))
				goto leave;

			epoch_block(global, cr, cb, ct);

			/*
			 * If the epoch has been updated, then a grace period
			 * requires that all threads are observed idle at the