Alter build process to rely on canaries only

With the react-sdk and js-sdk having their `npm start`s split out (as per https://github.com/matrix-org/matrix-react-sdk/pull/2175 and https://github.com/matrix-org/matrix-js-sdk/pull/742) we can trigger an initial build ourselves and start the watcher afterwards. This canary approach has a very slight speed increase over serially running all the commands as the watcher can be started as early as possible.

This all can be improved and potentially eliminated with a bit more planning, however: https://github.com/vector-im/riot-web/issues/7386

package-lock.json

@@ -384,12 +384,6 @@
       "integrity": "sha1-GdOGodntxufByF04iu28xW0zYC0=",
       "dev": true
     },
-    "async-lock": {
-      "version": "1.1.3",
-      "resolved": "https://registry.npmjs.org/async-lock/-/async-lock-1.1.3.tgz",
-      "integrity": "sha512-nxlfFLGfCJ1r7p9zhR5OuL6jYkDd9P7FqSitfLji+C1NdyhCz4+rWW3kiPiyPASHhN7VlsKEvRWWbnME9lYngw==",
-      "dev": true
-    },
     "asynckit": {
       "version": "0.4.0",
       "resolved": "https://registry.npmjs.org/asynckit/-/asynckit-0.4.0.tgz",
@@ -4180,12 +4174,14 @@
         "balanced-match": {
           "version": "1.0.0",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "brace-expansion": {
           "version": "1.1.11",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "balanced-match": "^1.0.0",
             "concat-map": "0.0.1"
@@ -4200,17 +4196,20 @@
         "code-point-at": {
           "version": "1.1.0",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "concat-map": {
           "version": "0.0.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "console-control-strings": {
           "version": "1.1.0",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "core-util-is": {
           "version": "1.0.2",
@@ -4327,7 +4326,8 @@
         "inherits": {
           "version": "2.0.3",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "ini": {
           "version": "1.3.5",
@@ -4339,6 +4339,7 @@
           "version": "1.0.0",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "number-is-nan": "^1.0.0"
           }
@@ -4353,6 +4354,7 @@
           "version": "3.0.4",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "brace-expansion": "^1.1.7"
           }
@@ -4360,7 +4362,8 @@
         "minimist": {
           "version": "0.0.8",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "minipass": {
           "version": "2.2.4",
@@ -4384,6 +4387,7 @@
           "version": "0.5.1",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "minimist": "0.0.8"
           }
@@ -4464,7 +4468,8 @@
         "number-is-nan": {
           "version": "1.0.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "object-assign": {
           "version": "4.1.1",
@@ -4597,6 +4602,7 @@
           "version": "1.0.2",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "code-point-at": "^1.0.0",
             "is-fullwidth-code-point": "^1.0.0",

package.json

@@ -81,7 +81,6 @@
     "url": "^0.11.0"
   },
   "devDependencies": {
-    "async-lock": "^1.1.3",
     "autoprefixer": "^6.6.0",
     "babel-cli": "^6.5.2",
     "babel-core": "^6.14.0",

scripts/block-on-sdk-build.js

@@ -1,19 +1,12 @@
 const path = require('path');
 const chokidar = require('chokidar');
-const AsyncLock = require('async-lock');
 
 
-// This script sits and waits for a build of an underlying SDK (js or react)
+// This script waits for a signal that an underlying SDK (js or react) has finished
-// to complete before exiting. This is done by cooperating with build-watch-sdk.js
+// enough of the build process to be safe to rely on. In riot-web's case, this means
-// by waiting for it's signal to start watching for file changes, then watching
+// that the underlying SDK has finished an initial build and is getting ready to watch
-// the SDK's build output for a storm of file changes to stop. Both the js-sdk
+// for changes. This is done through use of a canary file that is deleted when it is
-// and react-sdk compile each file one by one, so by waiting for file changes to
+// safe to continue (see build-watch-sdk.js for why we listen for a delete event).
-// stop we know it is safe to continue and therefore exit this script. We give
-// some leeway to the SDK's build process to handle larger/more complex files
-// through use of a reset-on-touch countdown timer. When a file change occurs,
-// we reset the countdown to WAIT_TIME and let it count down. If the count down
-// completes, we consider ourselves having left the file system update storm and
-// therefore can consider a build of the SDK to be fully completed.
 
 // Why do we block in the first place? Because if riot-web starts it's initial
 // build (via webpack-dev-server) and the react-sdk or js-sdk are halfway through
@@ -26,21 +19,12 @@ const AsyncLock = require('async-lock');
 // build which riot-web is waiting for. When complete, riot-web starts building as
 // per normal.
 
-// Why the canary to begin watching? Because we can't reliably determine that the
-// build triggered by `npm install` in each SDK is actually the process we need to
-// be watching for. To work around this, build-watch-sdk.js does the `npm install`
-// and follows through with a canary to signal to this script that it should start
-// watching for changes produced by that SDK's `npm start` (run immediately after
-// the canary is sent).
-
-
-const WAIT_TIME = 5000; // ms
 
 function waitForCanary(canaryName) {
     return new Promise((resolve, reject) => {
-        const filename = path.resolve(path.join(".tmp", canaryName));
+        const filename = path.resolve(path.join(".tmp", canaryName + ".canary"));
 
-        // See triggerCanarySignal in build-watch-sdk.js for why we watch for `unlink`
+        // See build-watch-sdk.js for why we listen for 'unlink' specifically.
         const watcher = chokidar.watch(filename).on('unlink', (path) => {
             console.log("[block-on-build] Received signal to start watching for builds");
             watcher.close();
@@ -49,31 +33,6 @@ function waitForCanary(canaryName) {
     });
 }
 
-function waitOnSdkBuild(sdkName) {
-    // First we wait for a local canary file to be changed
-    return waitForCanary(sdkName).then(() => new Promise((resolve, reject) => {
-        const buildDirectory = path.dirname(require.resolve(`matrix-${sdkName}-sdk`));
-        const lock = new AsyncLock();
-        let timerId = null;
-
-        const watcher = chokidar.watch(buildDirectory).on('all', (event, path) => {
-            lock.acquire("timer", (done) => {
-                if (timerId !== null) {
-                    //console.log("Resetting countdown");
-                    clearTimeout(timerId);
-                }
-                //console.log(`Waiting ${WAIT_TIME}ms for another file update...`);
-                timerId = setTimeout(() => {
-                    console.log("[block-on-build] No updates - unblocking");
-                    watcher.close();
-                    resolve();
-                }, WAIT_TIME);
-                done();
-            }, null, null);
-        });
-    }));
-}
-
 const sdkName = process.argv[2];
 if (!sdkName) {
     console.error("[block-on-build] No SDK name provided");
@@ -81,7 +40,7 @@ if (!sdkName) {
 }
 
 console.log("[block-on-build] Waiting for SDK: " + sdkName);
-waitOnSdkBuild(sdkName).then(() => {
+waitForCanary(sdkName).then(() => {
     console.log("[block-on-build] Unblocked");
     process.exit(0);
 });

scripts/build-watch-sdk.js

@@ -16,7 +16,15 @@ if (!sdkName) {
 }
 
 const sdkPath = path.dirname(require.resolve(`matrix-${sdkName}-sdk/package.json`));
-console.log(sdkPath);
+
+// Note: we intentionally create then delete the canary file to work
+// around a file watching problem where if the file exists on startup it
+// may fire a "created" event for the file. By having the behaviour be "do
+// something on delete" we avoid accidentally firing the signal too early.
+// We also need to ensure the create and delete events are not too close
+// together, otherwise the filesystem may not fire the watcher. Therefore
+// we create the canary as early as possible and delete it as late as possible.
+prepareCanarySignal(sdkName);
 
 // We only want to build the SDK if it looks like it was `npm link`ed
 if (fs.existsSync(path.join(sdkPath, '.git'))) {
@@ -37,25 +45,37 @@ if (fs.existsSync(path.join(sdkPath, '.git'))) {
         });
     }
 
-    // Send a signal so that the various blocks can unblock. See the top of
+    // Prepare an initial build of the SDK
-    // block-on-sdk-build.js for more information on how this is used.
+    child_process.execSync("npm run start:init", {
-    console.log("Sending signal that other processes may unblock");
-    triggerCanarySignal(sdkName);
-
-    // Actually start the watcher process for the sdk. This is what block-on-sdk-build.js
-    // is going to monitor.
-    console.log("Performing task: " + task);
-    child_process.execSync(`npm ${task === "build" ? "run build" : "start"}`, {
         env: process.env,
         cwd: sdkPath,
     });
-}
+
+    // Send a signal to unblock the build for other processes. Used by block-on-sdk-build.js
+    console.log("Sending signal that other processes may unblock");
+    triggerCanarySignal(sdkName);
+
+    // Actually start the watcher process for the SDK (without an initial build)
+    console.log("Performing task: " + task);
+    const watchTask = sdkName === 'js' ? "start:watch" : "start:all";
+    const buildTask = "build";
+    child_process.execSync(`npm run ${task === "build" ? buildTask : watchTask}`, {
+        env: process.env,
+        cwd: sdkPath,
+    });
+} else triggerCanarySignal(sdkName);
 
 function triggerCanarySignal(sdkName) {
-    const tmpPath = path.resolve(".tmp");
+    fs.unlinkSync(getCanaryPath(sdkName));
+}
+
+function prepareCanarySignal(sdkName) {
+    const canaryPath = getCanaryPath(sdkName);
+    const canaryDir = path.dirname(canaryPath);
 
     try {
-        fs.mkdirSync(tmpPath);
+        console.log("Creating canary temp path...");
+        fs.mkdirSync(canaryDir);
     } catch (e) {
         if (e.code !== 'EEXIST') {
             console.error(e);
@@ -63,12 +83,17 @@ function triggerCanarySignal(sdkName) {
         }
     }
 
-    // Note: we intentionally create then delete the file to work around
+    try {
-    // a file watching problem where if the file exists on startup it may
+        console.log("Creating canary file: " + canaryPath);
-    // fire a "created" event for the file. By having the behaviour be "do
-    // something on delete" we avoid accidentally firing the signal too
-    // early.
-    const canaryPath = path.join(tmpPath, sdkName);
         fs.closeSync(fs.openSync(canaryPath, 'w'));
-    fs.unlinkSync(canaryPath);
+    } catch (e) {
+        if (e.code !== 'EEXIST') {
+            console.error(e);
+            throw "Failed to create canary file";
+        }
+    }
+}
+
+function getCanaryPath(sdkName) {
+    return path.join(path.resolve(".tmp"), sdkName + ".canary");
 }