Proxy process.on("exit") to avoid MaxListenersExceededWarning

This fixes #30, working around node's MaxListenersExceededWarning by creating a "proxy" event emitter to forward `exit` events.

This is a more concise alternative to #34.

src/index.ts

@@ -3,6 +3,7 @@ import fs from "fs";
 import os from "os";
 import path from "path";
 import { Readable, ReadableOptions, Writable, WritableOptions } from "stream";
+import { EventEmitter } from "events";
 
 export class ReadAfterDestroyedError extends Error {}
 export class ReadAfterReleasedError extends Error {}
@@ -12,6 +13,12 @@ export interface ReadStreamOptions {
   encoding?: ReadableOptions["encoding"];
 }
 
+// Work around node's MaxListenersExceededWarning for highly concurrent
+// workloads by creating a "proxy" event emitter. See:
+// https://github.com/mike-marcacci/fs-capacitor/issues/30
+const processExitProxy = new EventEmitter() as EventEmitter;
+process.addListener("exit", () => processExitProxy.emit("exit"));
+
 export class ReadStream extends Readable {
   private _pos: number = 0;
   private _writeStream: WriteStream;
@@ -117,7 +124,7 @@ export class WriteStream extends Writable {
         }
 
         // Cleanup when the process exits or is killed.
-        process.addListener("exit", this._cleanupSync);
+        processExitProxy.addListener("exit", this._cleanupSync);
 
         this._fd = fd;
         this.emit("ready");
@@ -126,7 +133,7 @@ export class WriteStream extends Writable {
   }
 
   _cleanupSync = (): void => {
-    process.removeListener("exit", this._cleanupSync);
+    processExitProxy.removeListener("exit", this._cleanupSync);
 
     if (typeof this._fd === "number")
       try {
@@ -208,7 +215,7 @@ export class WriteStream extends Writable {
 
         // We avoid removing this until now in case an exit occurs while
         // asyncronously cleaning up.
-        process.removeListener("exit", this._cleanupSync);
+        processExitProxy.removeListener("exit", this._cleanupSync);
         callback(unlinkError || closeError || error);
       });
     });