Merge pull request #4345 from chu11/issue4343_future_wait_for_errno

libflux: return better errno in future wait path

Author: mergify[bot]

doc/man3/flux_future_get.rst

@@ -129,6 +129,9 @@ ETIMEDOUT
    A timeout passed to ``flux_future_wait_for()`` expired before the future
    was fulfilled.
 
+EDEADLOCK
+   ``flux_future_wait_for()`` would likely deadlock due to an
+   improperly initialized future.
 
 RESOURCES
 =========

doc/test/spell.en.pws

@@ -626,3 +626,4 @@ num
 gc
 tgz
 tmpfiles
+EDEADLOCK

src/common/libflux/future.c

@@ -481,11 +481,17 @@ int flux_future_wait_for (flux_future_t *f, double timeout)
         f->now->running = false;
     }
     if (!future_is_ready (f)) {
-        /* Typically this error should be "impossible", but can occur
-         * if the future does not get initialized properly to use the
-         * now reactor.
+        /* This block of code is reached b/c flux_reactor_run() on the
+         * "now" reactor returned >= 0 AND the future was
+         * not fulfilled, e.g.
+         * - no init callback was registered when future was created
+         * - the init callback didn't register any watchers
+         * - the registered watchers stopped themselves or called
+         *   flux_reactor_stop() without fulfilling the future.
+         * Return EDEADLOCK indicating that the future cannot be
+         * fulfilled.
          */
-        errno = EINVAL;
+        errno = EDEADLOCK;
         return -1;
     }
     return 0;

src/common/libflux/test/future.c

@@ -122,8 +122,8 @@ void test_simple (void)
     ok (!flux_future_is_ready (f),
         "flux_future_is_ready returns false");
     errno = 0;
-    ok (flux_future_wait_for (f, -1.0) < 0 && errno == EINVAL,
-        "flux_future_wait_for fails with EINVAL with timeout < 0");
+    ok (flux_future_wait_for (f, -1.0) < 0 && errno == EDEADLOCK,
+        "flux_future_wait_for fails with EDEADLOCK with timeout < 0");
     ok (!flux_future_is_ready (f),
         "flux_future_is_ready returns false");
     errno = 0;

src/common/libkvs/test/kvs_checkpoint.c

@@ -50,13 +50,13 @@ void errors (void)
 
     errno = 0;
     ok (kvs_checkpoint_lookup_get_rootref (f, &rootref) < 0
-        && errno == EINVAL,
+        && errno == EDEADLOCK,
         "kvs_checkpoint_lookup_get_rootref fails on unfulfilled future");
 
     errno = 0;
     double timestamp;
     ok (kvs_checkpoint_lookup_get_timestamp (f, &timestamp) < 0
-        && errno == EINVAL,
+        && errno == EDEADLOCK,
         "kvs_checkpoint_lookup_get_timestamp fails on unfulfilled future");
 
     flux_future_destroy (f);