feat(compartment-mapper): One concurrent read

endojs · Jul 26, 2023 · 29048a2 · 29048a2
1 parent cf668e2
commit 29048a2
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Showing 2 changed files with 19 additions and 4 deletions.
diff --git a/packages/compartment-mapper/src/node-powers.js b/packages/compartment-mapper/src/node-powers.js
@@ -40,15 +40,26 @@ const makeReadPowersSloppy = ({ fs, url = undefined, crypto = undefined }) => {
   const pathToFileURL =
     url === undefined ? fakePathToFileURL : url.pathToFileURL;
 
+  let readMutex = Promise.resolve(undefined);
+
   /**
    * @param {string} location
    */
   const read = async location => {
+    const promise = readMutex;
+    let release = Function.prototype;
+    readMutex = new Promise(resolve => {
+      release = resolve;
+    });
+    await promise;
+
+    const path = fileURLToPath(location);
     try {
-      const path = fileURLToPath(location);
+      // We await here to ensure that we release the mutex only after
+      // completing the read.
       return await fs.promises.readFile(path);
-    } catch (error) {
-      throw Error(error.message);
+    } finally {
+      release(undefined);
     }
   };
 

diff --git a/packages/compartment-mapper/test/scaffold.js b/packages/compartment-mapper/test/scaffold.js
@@ -15,7 +15,11 @@ import {
 } from '../index.js';
 import { makeReadPowers } from '../src/node-powers.js';
 
-export const readPowers = makeReadPowers({ fs, crypto, url });
+export const readPowers = makeReadPowers({
+  fs,
+  crypto,
+  url,
+});
 
 export const sanitizePaths = (text = '', tolerateLineChange = false) => {
   if (tolerateLineChange) {