From 68372808ae4966722b789d681226c422d98e8695 Mon Sep 17 00:00:00 2001
From: Jon Hammerskov <jon@hammerskov.dk>
Date: Tue, 1 Nov 2022 11:03:26 +0100
Subject: [PATCH] fix(core): atomic writes of nxdeps.json

When writing nxdeps.json prevent parallel processes from seing half-written files
and prevent half written files to be left in case of process crash tob

The issue marked as closed by this has not been reproducible, so
this fix was done based only on reading the issue description and
code inspection.

It may be that the problem is caused by something else, but even
if this PR turns out not to solve the problem it introduces very
little complexity, and should be completely safe, and with some
likelyhood will solve or at least improve the issue

If the problem persists this change will log some info about
the error that occurred but will proceed without saving the cache

ISSUES CLOSED: #9146
---
 .../nx/src/project-graph/nx-deps-cache.ts     | 43 ++++++++++++++++---
 1 file changed, 37 insertions(+), 6 deletions(-)

diff --git a/packages/nx/src/project-graph/nx-deps-cache.ts b/packages/nx/src/project-graph/nx-deps-cache.ts
index 6191782158775..985147afed085 100644
--- a/packages/nx/src/project-graph/nx-deps-cache.ts
+++ b/packages/nx/src/project-graph/nx-deps-cache.ts
@@ -1,9 +1,8 @@
 import { existsSync } from 'fs';
-import { ensureDirSync } from 'fs-extra';
+import { ensureDirSync, renameSync } from 'fs-extra';
 import { join } from 'path';
 import { performance } from 'perf_hooks';
-import { projectGraphCacheDirectory } from '../utils/cache-directory';
-import { directoryExists, fileExists } from '../utils/fileutils';
+import { NxJsonConfiguration } from '../config/nx-json';
 import {
   FileData,
   ProjectFileMap,
@@ -12,9 +11,14 @@ import {
   ProjectGraphExternalNode,
   ProjectGraphNode,
 } from '../config/project-graph';
-import { readJsonFile, writeJsonFile } from '../utils/fileutils';
-import { NxJsonConfiguration } from '../config/nx-json';
 import { ProjectsConfigurations } from '../config/workspace-json-project-json';
+import { projectGraphCacheDirectory } from '../utils/cache-directory';
+import {
+  directoryExists,
+  fileExists,
+  readJsonFile,
+  writeJsonFile,
+} from '../utils/fileutils';
 
 export interface ProjectGraphCache {
   version: string;
@@ -106,7 +110,34 @@ export function createCache(
 
 export function writeCache(cache: ProjectGraphCache): void {
   performance.mark('write cache:start');
-  writeJsonFile(nxDepsPath, cache);
+  let retry = 1;
+  let done = false;
+  do {
+    // write first to a unique temporary filename and then do a
+    // rename of the file to the correct filename
+    // this is to avoid any problems with half-written files
+    // in case of crash and/or partially written files due
+    // to multiple parallel processes reading and writing this file
+    const unique = (Math.random().toString(16) + '0000000').slice(2, 10);
+    const tmpDepsPath = `${nxDepsPath}~${unique}`;
+
+    try {
+      writeJsonFile(tmpDepsPath, cache);
+      renameSync(tmpDepsPath, nxDepsPath);
+      done = true;
+    } catch (err: any) {
+      if (err instanceof Error) {
+        console.log(
+          `ERROR (${retry}) when writing \n${err.message}\n${err.stack}`
+        );
+      } else {
+        console.log(
+          `ERROR  (${retry}) unknonw error when writing ${nxDepsPath}`
+        );
+      }
+      ++retry;
+    }
+  } while (!done && retry < 5);
   performance.mark('write cache:end');
   performance.measure('write cache', 'write cache:start', 'write cache:end');
 }