Harden JarCacheSupport

src/main/java/hudson/remoting/JarCacheSupport.java

@@ -85,8 +85,11 @@
         public void run() {
             try {
                 URL url = retrieve(channel, sum1, sum2);
-                inprogress.remove(key);
-                promise.complete(url);
+                if (inprogress.remove(key, promise)) {
+                    promise.complete(url);
+                } else {
+                    promise.completeExceptionally(new IllegalStateException("Download is (unexpectedly) no longer in progress"));
+                }
             } catch (ChannelClosedException | RequestAbortedException e) {
                 // the connection was killed while we were still resolving the file
                 bailout(e);
@@ -101,7 +104,7 @@
                     bailout(e);
                 } else {
                     // in other general failures, we aren't retrying
                     // TODO: or should we?
                     promise.completeExceptionally(e);
                     LOGGER.log(Level.WARNING, String.format("Failed to resolve a jar %016x%016x", sum1, sum2), e);
                 }
@@ -112,7 +115,7 @@
          * Report a failure of the retrieval and allows another thread to retry.
          */
         private void bailout(Throwable e) {
-            inprogress.remove(key);     // this lets another thread to retry later
+            inprogress.remove(key, promise);     // this lets another thread to retry later
             promise.completeExceptionally(e);             // then tell those who are waiting that we aborted
         }
     }