Bugfix: fix race conditions

utils/sync.ts

@@ -1,12 +1,68 @@
 import fs from "fs";
 import path from "path";
+import os from "os";
 import util from "util";
+import crypto from "crypto";
 import { exec } from "child_process";
 import { SyncFoldersSyncFnParams } from "../types";
 import grabDirNames from "./grab-dir-names";
+import { fldFileToStr } from "./grab-folders-files-string-paths";
+import delay from "./delay";
 
 const execPromise = util.promisify(exec);
 
+const LOCK_STALE_MS = 5 * 60 * 1000;
+const LOCK_RETRY_MS = 100;
+
+function lockPathFor(dirPath: string) {
+    const hash = crypto
+        .createHash("sha1")
+        .update(path.resolve(dirPath))
+        .digest("hex")
+        .slice(0, 16);
+
+    return path.join(os.tmpdir(), `turbosync-${hash}.lock`);
+}
+
+async function acquireLock(lockPath: string) {
+    while (true) {
+        try {
+            const fd = fs.openSync(lockPath, "wx");
+            fs.writeFileSync(fd, String(process.pid));
+            fs.closeSync(fd);
+            return;
+        } catch (error: any) {
+            if (error.code !== "EEXIST") throw error;
+
+            try {
+                const { mtimeMs } = fs.statSync(lockPath);
+                if (Date.now() - mtimeMs > LOCK_STALE_MS) {
+                    fs.unlinkSync(lockPath);
+                    continue;
+                }
+            } catch {
+                continue;
+            }
+
+            await delay(LOCK_RETRY_MS);
+        }
+    }
+}
+
+async function acquireLocks(lockPaths: string[]) {
+    for (const lockPath of lockPaths) {
+        await acquireLock(lockPath);
+    }
+}
+
+function releaseLocks(lockPaths: string[]) {
+    for (const lockPath of lockPaths) {
+        try {
+            fs.unlinkSync(lockPath);
+        } catch {}
+    }
+}
+
 export default async function sync({
     options,
     dirs,
@@ -94,11 +150,22 @@ export default async function sync({
         allCommandsArr.push(cmdArray);
     }
 
-    await Promise.all(
-        allCommandsArr.map((cmdArr) => {
-            return execPromise(cmdArr.join(" "));
-        })
-    );
+    const lockPaths = [dirPath, ...dstDirs.map((dr) => fldFileToStr(dr))]
+        .filter((pth): pth is string => Boolean(pth))
+        .map((pth) => lockPathFor(pth))
+        .sort();
+
+    await acquireLocks(lockPaths);
+
+    try {
+        await Promise.all(
+            allCommandsArr.map((cmdArr) => {
+                return execPromise(cmdArr.join(" "));
+            })
+        );
+    } finally {
+        releaseLocks(lockPaths);
+    }
 
     console.log(`${dirPath} Folder Sync Complete. Exiting ...`);
 }