S3: cancel the meta request before release the native handler (#764)

src/main/java/software/amazon/awssdk/crt/s3/S3MetaRequest.java

@@ -38,6 +38,13 @@ protected boolean canReleaseReferencesImmediately() {
     @Override
     protected void releaseNativeHandle() {
         if (!isNull()) {
+            /**
+             * Cancel the meta request before drop the refcount.
+             * The meta request is not referenced by Java any longer, everything from native to Java will be ignored.
+             * Cancelling the meta request instead of letting it keep flowing.
+             * Note: If the meta request has not finished yet, it will be finished with `AWS_ERROR_S3_CANCELED`.
+             **/
+            s3MetaRequestCancel(getNativeHandle());
             s3MetaRequestDestroy(getNativeHandle());
         }
     }

src/test/java/software/amazon/awssdk/crt/test/S3ExpressCredentialsProviderHandlerSample.java

@@ -67,8 +67,10 @@ public void onFinished(S3FinishedResponseContext context) {
                 .withMetaRequestType(MetaRequestType.DEFAULT).withHttpRequest(httpRequest)
                 .withResponseHandler(responseHandler).withSigningConfig(config);
 
-        try (S3MetaRequest metaRequest = client.makeMetaRequest(metaRequestOptions)) {
-        }
+        S3MetaRequest metaRequest = client.makeMetaRequest(metaRequestOptions);
+        future.whenComplete((r,t) -> {
+            metaRequest.close();
+        });
         return future;
 
     }