Style & Polish.

git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@2656 d4fa192b-c00b-0410-8231-f00ffab90ce4

bin/varnishd/cache_pool.c

@@ -28,7 +28,18 @@
  *
  * $Id$
  *
- * XXX: automatic thread-pool size adaptation.
+ * We maintain a number of worker thread pools, to spread lock contention.
+ *
+ * Pools can be added on the fly, as a means to mitigate lock contention,
+ * but can only be removed again by a restart. (XXX: we could fix that)
+ *
+ * Two threads herd the pools, one eliminates idle threads and aggregates
+ * statistics for all the pools, the other thread creates new threads
+ * on demand, subject to various numerical constraints.
+ *
+ * The algorithm for when to create threads needs to be reactive enough
+ * to handle startup spikes, but sufficiently attenuated to not cause
+ * thread pileups.  This remains subject for improvement.
  */
 
 #include "config.h"
@@ -188,24 +199,6 @@ WRK_Sendfile(struct worker *w, int fd, off_t off, unsigned len)
 
 /*--------------------------------------------------------------------*/
 
-static void
-wrk_do_cnt_sess(struct worker *w, void *priv)
-{
-	struct sess *sess;
-
-	CAST_OBJ_NOTNULL(sess, priv, SESS_MAGIC);
-	sess->wrk = w;
-	CHECK_OBJ_ORNULL(w->nobj, OBJECT_MAGIC);
-	CHECK_OBJ_ORNULL(w->nobjhead, OBJHEAD_MAGIC);
-	w->used = NAN;
-	CNT_Session(sess);
-	assert(!isnan(w->used));
-	CHECK_OBJ_ORNULL(w->nobj, OBJECT_MAGIC);
-	CHECK_OBJ_ORNULL(w->nobjhead, OBJHEAD_MAGIC);
-}
-
-/*--------------------------------------------------------------------*/
-
 static void *
 wrk_thread(void *priv)
 {
@@ -269,7 +262,11 @@ wrk_thread(void *priv)
 	return (NULL);
 }
 
-/*--------------------------------------------------------------------*/
+/*--------------------------------------------------------------------
+ * Queue a workrequest if possible.
+ *
+ * Return zero if the request was queued, negative if it wasn't.
+ */
 
 int
 WRK_Queue(struct workreq *wrq)
@@ -302,8 +299,7 @@ WRK_Queue(struct workreq *wrq)
 		return (0);
 	}
 
-	/* If we have too much in the overflow already, refuse */
-
+	/* If we have too much in the overflow already, refuse. */
 	if (qp->nqueue > ovfl_max) {
 		qp->ndrop++;
 		UNLOCK(&qp->mtx);
@@ -320,6 +316,24 @@ WRK_Queue(struct workreq *wrq)
 
 /*--------------------------------------------------------------------*/
 
+static void
+wrk_do_cnt_sess(struct worker *w, void *priv)
+{
+	struct sess *sess;
+
+	CAST_OBJ_NOTNULL(sess, priv, SESS_MAGIC);
+	sess->wrk = w;
+	CHECK_OBJ_ORNULL(w->nobj, OBJECT_MAGIC);
+	CHECK_OBJ_ORNULL(w->nobjhead, OBJHEAD_MAGIC);
+	w->used = NAN;
+	CNT_Session(sess);
+	assert(!isnan(w->used));
+	CHECK_OBJ_ORNULL(w->nobj, OBJECT_MAGIC);
+	CHECK_OBJ_ORNULL(w->nobjhead, OBJHEAD_MAGIC);
+}
+
+/*--------------------------------------------------------------------*/
+
 void
 WRK_QueueSession(struct sess *sp)
 {
@@ -346,7 +360,9 @@ WRK_QueueSession(struct sess *sp)
 	SES_Delete(sp);
 }
 
-/*--------------------------------------------------------------------*/
+/*--------------------------------------------------------------------
+ * Add (more) thread pools
+ */
 
 static void
 wrk_addpools(const unsigned pools)
@@ -466,7 +482,7 @@ wrk_herdtimer_thread(void *priv)
 }
 
 /*--------------------------------------------------------------------
- * Create more threads, if necessay & possible
+ * Create another thread, if necessary & possible
  */
 
 static void
@@ -540,6 +556,7 @@ WRK_Init(void)
 	AZ(pthread_mutex_init(&herder_mtx, NULL));
 
 	AZ(pthread_create(&tp, NULL, wrk_herdtimer_thread, NULL));
+	AZ(pthread_detach(tp));
 	AZ(pthread_create(&tp, NULL, wrk_herder_thread, NULL));
 	AZ(pthread_detach(tp));
 }