We had long-ago added a new loop type to libevent: EVLOOP_ONELOOP.

After talking with Brian, we're pretty sure that this is only because
really, really old libevent didn't allow bitwise or-ing of the other
loop types, because what we really need is (EVLOOP_ONCE |
EVLOOP_NONBLOCK).  And that's what EVLOOP_ONELOOP did (i.e., we
changed the logic of libevent's event.c to let ONELOOP do both ONCE
and NONBLOCK things).

In the new libevent version, we didn't implement EVLOOP_ONELOOP
properly.  As a result, and we got hangs in the SM BTL add_procs
function.  Note that the SM BTL wasn't to blame -- it was purely a
side-effect of bad ONELOOP integration (i.e., if you got past the SM
BTL add_procs, you may well have hung somewhere else).

This commit removes all ONELOOP customizations from event.c and
returns it to (almost) its original state from the libevent 2.0.7-rc
distribution.  Everwhere in the code base where we used ONELOOP, we
now use (ONCE | NONBLOCK).

This commit was SVN r23957.

ompi/runtime/ompi_mpi_finalize.c

@@ -144,7 +144,7 @@ int ompi_mpi_finalize(void)
     ompi_mpi_finalized = true;
 
 #if OMPI_ENABLE_PROGRESS_THREADS == 0
-    opal_progress_set_event_flag(OPAL_EVLOOP_ONELOOP);
+    opal_progress_set_event_flag(OPAL_EVLOOP_ONCE | OPAL_EVLOOP_NONBLOCK);
 #endif
 
     /* Redo ORTE calling opal_progress_event_users_increment() during

opal/mca/event/base/README.openmpi

@@ -66,16 +66,3 @@ m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])])
 
    This isn't critical, but it makes the compiler output MUCH
    prettier (and consistent with OMPI).
-
-7. Edit two files to add a new evloop option that OMPI uses
-   and doesn't exist in libevent:
-
-   libevent/event.c: change event_base_loop in two places by
-   adding EVLOOP_ONELOOP to the conditional:
-
-       if (!base->event_count_active && (flags & (EVLOOP_ONCE|EVLOOP_ONELOOP)))
-       .....
-       } else if (flags & (EVLOOP_NONBLOCK|EVLOOP_ONELOOP))
-
-   libevent/include/event2/event.h:
-       #define EVLOOP_ONELOOP 0x05

opal/mca/event/event.h

@@ -56,10 +56,6 @@ typedef unsigned short u_short;
 
 #define OPAL_EVLOOP_ONCE     0x01    /**< Block at most once. */
 #define OPAL_EVLOOP_NONBLOCK 0x02    /**< Do not block. */
-    /* run once through the loop, but do have the default timeout.
-     * Need to be both something special *AND* OPAL_EVLOOP_ONCE
-     */
-#define OPAL_EVLOOP_ONELOOP  0x05
 
 /* selected module will fill this typedef in with their
  * own definition of ev_struct

opal/mca/event/libevent207/libevent/event.c

@@ -1557,9 +1557,9 @@ event_base_loop(struct event_base *base, int flags)
 
 		if (N_ACTIVE_CALLBACKS(base)) {
 			event_process_active(base);
-			if (!base->event_count_active && (flags & (EVLOOP_ONCE|EVLOOP_ONELOOP)))
+			if (!base->event_count_active && (flags & EVLOOP_ONCE))
 				done = 1;
-                } else if (flags & (EVLOOP_NONBLOCK|EVLOOP_ONELOOP))
+                } else if (flags & EVLOOP_NONBLOCK)
 			done = 1;
 	}
 	event_debug(("%s: asked to terminate loop.", __func__));

opal/mca/event/libevent207/libevent/include/event2/event.h

@@ -308,9 +308,6 @@ int event_base_set(struct event_base *, struct event *);
 /*@{*/
 #define EVLOOP_ONCE	0x01	/**< Block at most once. */
 #define EVLOOP_NONBLOCK	0x02	/**< Do not block. */
-    /* run once through the loop, but do have the default timeout.
-     *        Need to be both something special *AND* EVLOOP_ONCE */
-#define EVLOOP_ONELOOP     0x05
 /*@}*/
 
 /**

opal/runtime/opal_progress.c

@@ -37,7 +37,7 @@
 /* 
  * default parameters 
  */
-static int opal_progress_event_flag = OPAL_EVLOOP_ONELOOP;
+static int opal_progress_event_flag = OPAL_EVLOOP_ONCE | OPAL_EVLOOP_NONBLOCK;
 volatile int32_t opal_progress_thread_count = 0;
 int opal_progress_spin_count = 10000;