[PATCH 1/2] define PMIX_Ring behavior in singleton mode

contribs/pmi2/pmi2_api.c

@@ -656,6 +656,15 @@ int PMIX_Ring(const char value[], int *rank, int *ranks, char left[], char right
 
     PMI2U_printf("[BEGIN PMI2_Ring]");
 
+    /* for singleton mode, set rank and ranks, copy input to output buffers */
+    if (PMI2_initialized == SINGLETON_INIT_BUT_NO_PM) {
+        *rank  = 0;
+        *ranks = 1;
+        MPIU_Strncpy(left,  value, maxvalue);
+        MPIU_Strncpy(right, value, maxvalue);
+        goto fn_exit_singleton;
+    }
+
     /* send message: cmd=ring_in, count=1, left=value, right=value */
     pmi2_errno = PMIi_WriteSimpleCommandStr(PMI2_fd, &cmd, RING_CMD,
 	RING_COUNT_KEY,   "1",
@@ -689,6 +698,7 @@ int PMIX_Ring(const char value[], int *rank, int *ranks, char left[], char right
 fn_exit:
     free(cmd.command);
     freepairs(cmd.pairs, cmd.nPairs);
+fn_exit_singleton:
     PMI2U_printf("[END PMI2_Ring]");
     return pmi2_errno;
 fn_fail:

contribs/pmi2/slurm/pmi2.h

@@ -426,8 +426,8 @@ int PMI2_Job_Disconnect(const char jobid[]);
  
   Output Parameters:
   + rank  - returns caller's rank within ring
-  - ranks - returns number of procs within ring
-  - left  - buffer to receive value provided by (rank - 1) % ranks
+  . ranks - returns number of procs within ring
+  . left  - buffer to receive value provided by (rank - 1) % ranks
   - right - buffer to receive value provided by (rank + 1) % ranks
  
   Return values:
@@ -440,6 +440,14 @@ int PMI2_Job_Disconnect(const char jobid[]);
   function, but a process may return before all processes have called
   the function.
 
+  The rank of a process within the ring may not be the same as its
+  rank returned by PMI2_Init.
+
+  For a process group consisting of a single process, this function
+  returns rank=0, ranks=1, and the input string in the value buffer
+  shall be copied to the left and right output buffers.  This same
+  behavior holds when the function is called in singleton mode.
+
 @*/
 #define HAVE_PMIX_RING 1 /* so one can conditionally compile with this funciton */
 int PMIX_Ring(const char value[], int *rank, int *ranks, char left[], char right[], int maxvalue);