MPMs unix: bind the bucket number of each child to its slot number

We need not remember each child's bucket number in SHM for restarts, for the
lifetime of the httpd main process the bucket number can be bound to the slot
number such that: bucket = slot % num_buckets.

This both simplifies the logic and helps children maintenance per bucket in
threaded MPMs, where previously perform_idle_server_maintenance() could create
or kill children processes for the buckets it was not in charge of.

diff --git a/include/scoreboard.h b/include/scoreboard.h
index 57cf3df..b714a8c 100644
--- a/include/scoreboard.h
+++ b/include/scoreboard.h
@@ -143,7 +143,9 @@ struct process_score {
     apr_uint32_t lingering_close;   /* async connections in lingering close */
     apr_uint32_t keep_alive;        /* async connections in keep alive */
     apr_uint32_t suspended;         /* connections suspended by some module */
-    int bucket;             /* Listener bucket used by this child */
+    int bucket;  /* Listener bucket used by this child; this field is DEPRECATED
+                  * and no longer updated by the MPMs (i.e. always zero).
+                  */
 };
 
 /* Scoreboard is now in 'local' memory, since it isn't updated once created,
diff --git a/server/mpm/event/event.c b/server/mpm/event/event.c
index ffe8a23..048ae61 100644
--- a/server/mpm/event/event.c
+++ b/server/mpm/event/event.c
@@ -2695,7 +2695,6 @@ static int make_child(server_rec * s, int slot, int bucket)
 
     ap_scoreboard_image->parent[slot].quiescing = 0;
     ap_scoreboard_image->parent[slot].not_accepting = 0;
-    ap_scoreboard_image->parent[slot].bucket = bucket;
     event_note_child_started(slot, pid);
     active_daemons++;
     retained->total_daemons++;
@@ -2734,6 +2733,7 @@ static void perform_idle_server_maintenance(int child_bucket, int num_buckets)
          * that threads_per_child is always > 0 */
         int status = SERVER_DEAD;
         int child_threads_active = 0;
+        int bucket = i % num_buckets;
 
         if (i >= retained->max_daemons_limit &&
             free_length == retained->idle_spawn_rate[child_bucket]) {
@@ -2757,7 +2757,7 @@ static void perform_idle_server_maintenance(int child_bucket, int num_buckets)
                  */
                 if (status <= SERVER_READY && !ps->quiescing && !ps->not_accepting
                     && ps->generation == retained->mpm->my_generation
-                    && ps->bucket == child_bucket)
+                    && bucket == child_bucket)
                 {
                     ++idle_thread_count;
                 }
@@ -2768,7 +2768,9 @@ static void perform_idle_server_maintenance(int child_bucket, int num_buckets)
             last_non_dead = i;
         }
         active_thread_count += child_threads_active;
-        if (!ps->pid && free_length < retained->idle_spawn_rate[child_bucket])
+        if (!ps->pid
+                && bucket == child_bucket
+                && free_length < retained->idle_spawn_rate[child_bucket])
             free_slots[free_length++] = i;
         else if (child_threads_active == threads_per_child)
             had_healthy_child = 1;
@@ -2951,13 +2953,14 @@ static void server_main_loop(int remaining_children_to_start, int num_buckets)
                 retained->total_daemons--;
                 if (processed_status == APEXIT_CHILDSICK) {
                     /* resource shortage, minimize the fork rate */
-                    retained->idle_spawn_rate[ps->bucket] = 1;
+                    retained->idle_spawn_rate[child_slot % num_buckets] = 1;
                 }
                 else if (remaining_children_to_start) {
                     /* we're still doing a 1-for-1 replacement of dead
                      * children with new children
                      */
-                    make_child(ap_server_conf, child_slot, ps->bucket);
+                    make_child(ap_server_conf, child_slot,
+                               child_slot % num_buckets);
                     --remaining_children_to_start;
                 }
             }
diff --git a/server/mpm/prefork/prefork.c b/server/mpm/prefork/prefork.c
index 8efda72..7c00625 100644
--- a/server/mpm/prefork/prefork.c
+++ b/server/mpm/prefork/prefork.c
@@ -637,8 +637,9 @@ static void child_main(int child_num_arg, int child_bucket)
 }
 
 
-static int make_child(server_rec *s, int slot, int bucket)
+static int make_child(server_rec *s, int slot)
 {
+    int bucket = slot % retained->mpm->num_buckets;
     int pid;
 
     if (slot + 1 > retained->max_daemons_limit) {
@@ -716,7 +717,6 @@ static int make_child(server_rec *s, int slot, int bucket)
         child_main(slot, bucket);
     }
 
-    ap_scoreboard_image->parent[slot].bucket = bucket;
     prefork_note_child_started(slot, pid);
 
     return 0;
@@ -732,7 +732,7 @@ static void startup_children(int number_to_start)
         if (ap_scoreboard_image->servers[i][0].status != SERVER_DEAD) {
             continue;
         }
-        if (make_child(ap_server_conf, i, i % retained->mpm->num_buckets) < 0) {
+        if (make_child(ap_server_conf, i) < 0) {
             break;
         }
         --number_to_start;
@@ -741,8 +741,6 @@ static void startup_children(int number_to_start)
 
 static void perform_idle_server_maintenance(apr_pool_t *p)
 {
-    static int bucket_make_child_record = -1;
-    static int bucket_kill_child_record = -1;
     int i;
     int idle_count;
     worker_score *ws;
@@ -789,6 +787,7 @@ static void perform_idle_server_maintenance(apr_pool_t *p)
     }
     retained->max_daemons_limit = last_non_dead + 1;
     if (idle_count > ap_daemons_max_free) {
+        static int bucket_kill_child_record = -1;
         /* kill off one child... we use the pod because that'll cause it to
          * shut down gracefully, in case it happened to pick up a request
          * while we were counting
@@ -819,10 +818,7 @@ static void perform_idle_server_maintenance(apr_pool_t *p)
                     idle_count, total_non_dead);
             }
             for (i = 0; i < free_length; ++i) {
-                bucket_make_child_record++;
-                bucket_make_child_record %= retained->mpm->num_buckets;
-                make_child(ap_server_conf, free_slots[i],
-                           bucket_make_child_record);
+                make_child(ap_server_conf, free_slots[i]);
             }
             /* the next time around we want to spawn twice as many if this
              * wasn't good enough, but not if we've just done a graceful
@@ -867,7 +863,7 @@ static int prefork_run(apr_pool_t *_pconf, apr_pool_t *plog, server_rec *s)
 
     if (one_process) {
         AP_MONCONTROL(1);
-        make_child(ap_server_conf, 0, 0);
+        make_child(ap_server_conf, 0);
         /* NOTREACHED */
         ap_assert(0);
         return !OK;
@@ -976,8 +972,7 @@ static int prefork_run(apr_pool_t *_pconf, apr_pool_t *plog, server_rec *s)
                     /* we're still doing a 1-for-1 replacement of dead
                      * children with new children
                      */
-                    make_child(ap_server_conf, child_slot,
-                               ap_get_scoreboard_process(child_slot)->bucket);
+                    make_child(ap_server_conf, child_slot);
                     --remaining_children_to_start;
                 }
 #if APR_HAS_OTHER_CHILD
diff --git a/server/mpm/worker/worker.c b/server/mpm/worker/worker.c
index 8012fe2..a927942 100644
--- a/server/mpm/worker/worker.c
+++ b/server/mpm/worker/worker.c
@@ -1339,7 +1339,6 @@ static int make_child(server_rec *s, int slot, int bucket)
         worker_note_child_lost_slot(slot, pid);
     }
     ap_scoreboard_image->parent[slot].quiescing = 0;
-    ap_scoreboard_image->parent[slot].bucket = bucket;
     worker_note_child_started(slot, pid);
     return 0;
 }
@@ -1388,6 +1387,7 @@ static void perform_idle_server_maintenance(int child_bucket, int num_buckets)
         int any_dead_threads = 0;
         int all_dead_threads = 1;
         int child_threads_active = 0;
+        int bucket = i % num_buckets;
 
         if (i >= retained->max_daemons_limit &&
             totally_free_length == retained->idle_spawn_rate[child_bucket]) {
@@ -1420,7 +1420,7 @@ static void perform_idle_server_maintenance(int child_bucket, int num_buckets)
                 if (status <= SERVER_READY &&
                         !ps->quiescing &&
                         ps->generation == retained->mpm->my_generation &&
-                        ps->bucket == child_bucket) {
+                        bucket == child_bucket) {
                     ++idle_thread_count;
                 }
                 if (status >= SERVER_READY && status < SERVER_GRACEFUL) {
@@ -1430,6 +1430,7 @@ static void perform_idle_server_maintenance(int child_bucket, int num_buckets)
         }
         active_thread_count += child_threads_active;
         if (any_dead_threads
+                && bucket == child_bucket
                 && totally_free_length < retained->idle_spawn_rate[child_bucket]
                 && free_length < MAX_SPAWN_RATE / num_buckets
                 && (!ps->pid               /* no process in the slot */
@@ -1615,14 +1616,15 @@ static void server_main_loop(int remaining_children_to_start, int num_buckets)
                 ps->quiescing = 0;
                 if (processed_status == APEXIT_CHILDSICK) {
                     /* resource shortage, minimize the fork rate */
-                    retained->idle_spawn_rate[ps->bucket] = 1;
+                    retained->idle_spawn_rate[child_slot % num_buckets] = 1;
                 }
                 else if (remaining_children_to_start
                     && child_slot < ap_daemons_limit) {
                     /* we're still doing a 1-for-1 replacement of dead
                      * children with new children
                      */
-                    make_child(ap_server_conf, child_slot, ps->bucket);
+                    make_child(ap_server_conf, child_slot,
+                               child_slot % num_buckets);
                     --remaining_children_to_start;
                 }
             }
-- 
2.19.1

