Implement flushSync to flush logs when running inside of Cloud functions

pinoSeqStream.js

@@ -12,6 +12,10 @@ let LEVEL_NAMES = {
   60: 'Fatal'
 };
 
+function msleep(n) {
+  Atomics.wait(new Int32Array(new SharedArrayBuffer(4)), 0, 0, n);
+}
+
 class PinoSeqStream extends stream.Writable {
   constructor(config) {
     super();
@@ -96,6 +100,30 @@ class PinoSeqStream extends stream.Writable {
     }
   }
 
+  // When flushing logs pino doesn't actually call _final and wait for the logs to flush when using streams
+  // Instead it calls a poorly documented flushSync method that is not part of the stream.Writable interface
+  // As the name suggests the function is not async and will block the event loop until the logs are flushed
+  // Normally this wouldn't be an issue, but when running inside a Cloud function the function will often exit before the logs are flushed,
+  // so this implementation is in line with what pino recommends https://getpino.io/#/docs/asynchronous?id=aws-lambda
+  flushSync() {
+    this.flushBuffer();
+
+    let running = true;
+    this._logger
+      .flush()
+      .then(() => {
+        running = false;
+      })
+      .catch((err) => {
+        console.error(err);
+        running = false;
+      });
+
+    while (running) {
+      msleep(100);
+    }
+  }
+
   // Force the underlying logger to flush at the time of the call
   // and wait for pending writes to complete
   _final(callback) {