element-web/scripts/block-on-sdk-build.js
Travis Ralston 2b037ee146 Prevent races by blocking on SDK builds
If we don't block on SDK builds, then the riot-web build fails due to half-built dependencies. This needs to be done at two levels: the js-sdk because it is used by both the react-sdk and riot-web, and at the react-sdk because riot-web needs it. This means our build process is synchronous for js -> react -> riot, at least for the initial build. 

This does increase the startup time, particularly because the file watch timer is at 5 seconds. The timer is used to detect a storm of file changes in the underlying SDKs and give the build process some room to compile larger files if needed. 

The file watcher is accompanied by a "canary signal file" to prevent the build-blocking script from unblocking too early. Both the js and react SDKs build when `npm install` is run, so we ensure that we only listen for the `npm start` build for each SDK.

This is all done at the riot level instead of at the individual SDK levels (where we could use a canary file to signal up the stack) because:
* babel (used by the js-sdk) doesn't really provide an "end up build" signal
* webpack is a bit of a nightmare to get it to behave at times
* this blocking approach is really only applicable to riot-web, although may be useful to some other projects.

Hopefully that all makes sense.
2018-09-24 17:12:42 -06:00

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JavaScript

const path = require('path');
const chokidar = require('chokidar');
const AsyncLock = require('async-lock');
const WAIT_TIME = 5000; // ms
function waitForCanary(canaryName) {
return new Promise((resolve, reject) => {
const filename = path.resolve(path.join(".tmp", canaryName));
// See triggerCanarySignal in build-watch-sdk.js for why we watch for `unlink`
const watcher = chokidar.watch(filename).on('unlink', (path) => {
console.log("[block-on-build] Received signal to start watching for builds");
watcher.close();
resolve();
});
});
}
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");
process.exit(1);
}
console.log("[block-on-build] Waiting for SDK: " + sdkName);
waitOnSdkBuild(sdkName).then(() => {
console.log("[block-on-build] Unblocked");
process.exit(0);
});