[jira] [Commented] (TINKERPOP-2569) Reconnect to server if Java driver fails to initialize

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/TINKERPOP-2569?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17424186#comment-17424186 ] 

ASF GitHub Bot commented on TINKERPOP-2569:
-------------------------------------------

xiazcy commented on a change in pull request #1476:
URL: https://github.com/apache/tinkerpop/pull/1476#discussion_r721719083



##########
File path: gremlin-driver/src/main/java/org/apache/tinkerpop/gremlin/driver/Client.java
##########
@@ -526,18 +527,24 @@ protected void initializeImplementation() {
 
             try {
                 CompletableFuture.allOf(cluster.allHosts().stream()
-                        .map(host -> CompletableFuture.runAsync(() -> initializeConnectionSetupForHost.accept(host), hostExecutor))
-                        .toArray(CompletableFuture[]::new))
+                                .map(host -> CompletableFuture.runAsync(() -> initializeConnectionSetupForHost.accept(host), hostExecutor))
+                                .toArray(CompletableFuture[]::new))
                         .join();
             } catch (CompletionException ex) {
-                Throwable cause;
-                Throwable result = ex;
-                if (null != (cause = ex.getCause())) {
-                    result = cause;
-                }
+                logger.error("", (ex.getCause() == null) ? ex : ex.getCause());
+            }
 
-                logger.error("", result);
-            } finally {
+            // throw an error if there is no host available after initializing connection pool.
+            if (cluster.availableHosts().isEmpty()) {
+                throw new NoHostAvailableException();

Review comment:
       I've missed this, thanks! I've put it back in the finally clause.




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> Reconnect to server if Java driver fails to initialize
> ------------------------------------------------------
>
>                 Key: TINKERPOP-2569
>                 URL: https://issues.apache.org/jira/browse/TINKERPOP-2569
>             Project: TinkerPop
>          Issue Type: Bug
>          Components: driver
>    Affects Versions: 3.4.11
>            Reporter: Stephen Mallette
>            Priority: Minor
>
> As reported here on SO: https://stackoverflow.com/questions/67586427/how-to-recover-with-a-retry-from-gremlin-nohostavailableexception
> If the host is unavailable at {{Client}} initialization then the host is not put in a state where reconnect is possible. Essentially, this test for {{GremlinServerIntegrateTest}} should pass:
> {code}
> @Test
>     public void shouldFailOnInitiallyDeadHost() throws Exception {
>         // start test with no server
>         this.stopServer();
>         final Cluster cluster = TestClientFactory.build().create();
>         final Client client = cluster.connect();
>         try {
>             // try to re-issue a request now that the server is down
>             client.submit("g").all().get(3000, TimeUnit.MILLISECONDS);
>             fail("Should throw an exception.");
>         } catch (RuntimeException re) {
>             // Client would have no active connections to the host, hence it would encounter a timeout
>             // trying to find an alive connection to the host.
>             assertThat(re.getCause(), instanceOf(NoHostAvailableException.class));
>             //
>             // should recover when the server comes back
>             //
>             // restart server
>             this.startServer();
>             // try a bunch of times to reconnect. on slower systems this may simply take longer...looking at you travis
>             for (int ix = 1; ix < 11; ix++) {
>                 // the retry interval is 1 second, wait a bit longer
>                 TimeUnit.SECONDS.sleep(5);
>                 try {
>                     final List<Result> results = client.submit("1+1").all().get(3000, TimeUnit.MILLISECONDS);
>                     assertEquals(1, results.size());
>                     assertEquals(2, results.get(0).getInt());
>                 } catch (Exception ex) {
>                     if (ix == 10)
>                         fail("Should have eventually succeeded");
>                 }
>             }
>         } finally {
>             cluster.close();
>         }
>     }
> {code}
> Note that there is a similar test that first allows a connect to a host and then kills it and then restarts it again called {{shouldFailOnDeadHost()}} which demonstrates that reconnection works in that situation.
> I thought it might be an easy to fix to simply call {{considerHostUnavailable()}} in the {{ConnectionPool}} constructor in the event of a {{CompletionException}} which should kickstart the reconnect process. The reconnects started firing but they all failed for some reason. I didn't have time to investigate further than than. 
> Currently the only workaround is to recreate the `Client` if this sort of situation occurs.



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