#2 Initial version.

src/main/caches/FSContentCache.ts

@@ -1,9 +1,13 @@
 import Promise from 'bluebird';
 import {createReadStream, createWriteStream, existsSync} from 'fs';
+import {has} from 'lodash';
 import {join} from 'path';
+import {AutoReleaseSemaphore} from '../utils/Semaphore';
 import {ContentCache} from './ContentCache';
 
 export class FSContentCache implements ContentCache {
+  // FIXME implement file locks
+  private _locks: {[key: string]: AutoReleaseSemaphore} = {};
 
   constructor(private _cacheDir: string) {}
 
@@ -12,11 +16,26 @@ export class FSContentCache implements ContentCache {
   }
 
   public getItem(itemKey: string): Promise<NodeJS.ReadableStream> {
+    if (has(this._locks, itemKey)) {
+      return this._locks[itemKey].acquire(() => {
+        return Promise.resolve(createReadStream(this._getItemPath(itemKey)));
+      });
+    }
     return Promise.resolve(createReadStream(this._getItemPath(itemKey)));
   }
 
   public setItem(itemKey: string): Promise<NodeJS.WritableStream> {
-    return Promise.resolve(createWriteStream(this._getItemPath(itemKey)));
+    if (has(this._locks, itemKey)) {
+      throw new Error('How you get to this path?');
+    }
+    this._locks[itemKey] = new AutoReleaseSemaphore(1);
+    const writeStream = createWriteStream(this._getItemPath(itemKey));
+    this._locks[itemKey].acquire(() => new Promise((res) => {
+      writeStream.on('finish', () => {
+        res();
+      });
+    }));
+    return Promise.resolve(writeStream);
   }
 
   private _getItemPath(itemKey: string): string {