Allow concurrent exports (#2181)

* Allow concurrent exports

* Bump version

Author: trask

agent/agent-tooling/src/main/java/com/microsoft/applicationinsights/agent/internal/telemetry/BatchSpanProcessor.java

@@ -232,6 +232,28 @@ private CompletableResultCode shutdown() {
     }
 
     private CompletableResultCode forceFlush() {
+      CompletableResultCode overallResult = new CompletableResultCode();
+      CompletableResultCode workerResult = forceFlushWorker();
+      workerResult.whenComplete(
+          () -> {
+            if (!workerResult.isSuccess()) {
+              overallResult.fail();
+              return;
+            }
+            CompletableResultCode exporterResult = spanExporter.flush();
+            exporterResult.whenComplete(
+                () -> {
+                  if (exporterResult.isSuccess()) {
+                    overallResult.succeed();
+                  } else {
+                    overallResult.fail();
+                  }
+                });
+          });
+      return overallResult;
+    }
+
+    private CompletableResultCode forceFlushWorker() {
       CompletableResultCode flushResult = new CompletableResultCode();
       // we set the atomic here to trigger the worker loop to do a flush of the entire queue.
       if (flushRequested.compareAndSet(null, flushResult)) {