Mailing List Archive

commit 9c0abf0c8065c2dab42410475346e7dff2156bc7
Author: AlveElde <alve_elde@hotmail.com>
Date: Fri Mar 22 11:21:46 2024 +0100

expire: Introduce EXP_Reduce()

This commit introduces EXP_Reduce(), a function to reduce object timers.
The goal is to provide a function better suited to soft-purging objects,
as EXP_Rearm() has some non-obvious disadvantages when used or this
purpose.

When EXP_Rearm() is used to soft-purge an object by setting its TTL to
0, the expiry is effectively reset to the start of the objects grace
period. This happens because the object TTL includes a time delta
between object insertion time (oc->t_origin) and now. The result is that
a soft-purge extends the lifetime of an already stale object, and
repeated soft-purges can keep the object away from expiry indefinitely.

The EXP_Reduce() function is better suited for soft-purging, as it only
updates an objects TTL if it would reduce the objects lifetime. The
function also has facilities for reducing grace and keep.

diff --git a/bin/varnishd/cache/cache_expire.c b/bin/varnishd/cache/cache_expire.c
index fb823e3cc..eb862bf49 100644
--- a/bin/varnishd/cache/cache_expire.c
+++ b/bin/varnishd/cache/cache_expire.c
@@ -219,6 +219,28 @@ EXP_Insert(struct worker *wrk, struct objcore *oc)
}
}

+/*--------------------------------------------------------------------
+ * Reduce object timers
+ */
+
+void
+EXP_Reduce(struct objcore *oc, vtim_real now,
+ vtim_dur ttl, vtim_dur grace, vtim_dur keep)
+{
+
+ CHECK_OBJ_NOTNULL(oc, OBJCORE_MAGIC);
+ assert(oc->refcnt > 0);
+
+ if (!isnan(ttl) && now + ttl - oc->t_origin >= oc->ttl)
+ ttl = NAN;
+ if (!isnan(grace) && grace >= oc->grace)
+ grace = NAN;
+ if (!isnan(keep) && keep >= oc->keep)
+ keep = NAN;
+
+ EXP_Rearm(oc, now, ttl, grace, keep);
+}
+
/*--------------------------------------------------------------------
* We have changed one or more of the object timers, tell the exp_thread
*
diff --git a/bin/varnishd/cache/cache_varnishd.h b/bin/varnishd/cache/cache_varnishd.h
index d759f95e7..61d3145c9 100644
--- a/bin/varnishd/cache/cache_varnishd.h
+++ b/bin/varnishd/cache/cache_varnishd.h
@@ -240,6 +240,8 @@ void EXP_Remove(struct objcore *, const struct objcore *);
/* cache_exp.c */
void EXP_Rearm(struct objcore *oc, vtim_real now,
vtim_dur ttl, vtim_dur grace, vtim_dur keep);
+void EXP_Reduce(struct objcore *oc, vtim_real now,
+ vtim_dur ttl, vtim_dur grace, vtim_dur keep);

/* From cache_main.c */
void BAN_Init(void);
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