(copied from an e-mail, just so that I don't have to re-type the

entire explanation ;-) )

Our Abaqus friends just pointed out another bug to me.  We have the
"-x" option to orterun to export environment variables to
newly-started processes.  However, it doesn't work if the environment
variable is already set in the target environment.  For example:

         mpirun -x LD_LIBRARY_PATH -np 2 a.out

The app context correctly contains LD_LIBRARY_PATH and its value, and
that app context correctly propagates out to the orted and is present
when we fork/exec a.out.  However, if LD_LIBRARY_PATH is already set
in the newly-started process' environment, the fork pls won't override
it with the value from the app context.

It really only has to do with the ordering of arguments in
ompi_environ_merge() -- when merging to env arrays together, we
"prefer" one set to the other if there are duplicate names.  I think
that if the user wants to override variables (even variables like
LD_LIBRARY_PATH), we should let them -- it's necessary for some
applications (like in Abaqus' case).  If they screw it up, it's their
fault (e.g., setting some LD_LIBRARY_PATH that won't work).

That being said, we should *not* allow them to override specific MCA
parameters that are necessary for startup -- that's easy to accomplish
by setting up that stuff *after* we merge in the context app
environment.

Also note that I am *only* speaking about the fork pls here -- so this
only applies to started ORTE job processes, not the orted.

So an easy re-order to do the following:

   env_copy = merge(environ and context->app)
   ompi_setenv(...MCA params necessary for startup..., env_copy)
   execve(..., env_copy)

does what we want.

This commit was SVN r5878.

src/mca/pls/fork/pls_fork_module.c

@@ -144,7 +144,7 @@ static int orte_pls_fork_proc(
     if(pid == 0) {
         char* param;
         char* uri;
-        char **new_env, **environ_copy;
+        char **environ_copy;
 
 #if 0
         /* for gperf - setup a new directory for each executable */
@@ -164,8 +164,13 @@ static int orte_pls_fork_proc(
         }
 #endif
 
-        /* setup base environment */
-        environ_copy = ompi_argv_copy(environ);
+        /* setup base environment: copy the current environ and merge
+           in the app context environ */
+        if (NULL != context->env) {
+            environ_copy = ompi_environ_merge(environ, context->env);
+        } else {
+            environ_copy = ompi_argv_copy(environ);
+        }
         param = mca_base_param_environ_variable("rmgr","bootproxy","jobid");
         ompi_unsetenv(param, &environ_copy);
 
@@ -190,7 +195,7 @@ static int orte_pls_fork_proc(
         ompi_setenv(param, uri, true, &environ_copy);
         free(param);
         free(uri);
-                                                                                                    
+
         /* setup gpr contact info */
         if(NULL != orte_process_info.gpr_replica_uri) {
             uri = strdup(orte_process_info.gpr_replica_uri);
@@ -209,10 +214,6 @@ static int orte_pls_fork_proc(
         /* setup stdout/stderr */
         orte_iof_base_setup_child(&opts);
 
-        /* execute application */
-        new_env = ompi_environ_merge(context->env, environ_copy);
-        ompi_argv_free(environ_copy);
-
         if (context->argv == NULL) {
             context->argv = malloc(sizeof(char*)*2);
             context->argv[0] = strdup(context->app);
@@ -242,7 +243,7 @@ static int orte_pls_fork_proc(
 
         /* Exec the new executable */
 
-        execve(context->app, context->argv, new_env);
+        execve(context->app, context->argv, environ_copy);
         ompi_output(0, "orte_pls_fork: %s - %s\n", context->app, 
             ompi_argv_join(context->argv, ' '));
         ompi_output(0, "orte_pls_fork: execv failed with errno=%d\n", errno);