--- /dev/null
+"use strict";
+
+// rawAsap provides everything we need except exception management.
+var rawAsap = require("./raw");
+// RawTasks are recycled to reduce GC churn.
+var freeTasks = [];
+// We queue errors to ensure they are thrown in right order (FIFO).
+// Array-as-queue is good enough here, since we are just dealing with exceptions.
+var pendingErrors = [];
+var requestErrorThrow = rawAsap.makeRequestCallFromTimer(throwFirstError);
+
+function throwFirstError() {
+ if (pendingErrors.length) {
+ throw pendingErrors.shift();
+ }
+}
+
+/**
+ * Calls a task as soon as possible after returning, in its own event, with priority
+ * over other events like animation, reflow, and repaint. An error thrown from an
+ * event will not interrupt, nor even substantially slow down the processing of
+ * other events, but will be rather postponed to a lower priority event.
+ * @param {{call}} task A callable object, typically a function that takes no
+ * arguments.
+ */
+module.exports = asap;
+function asap(task) {
+ var rawTask;
+ if (freeTasks.length) {
+ rawTask = freeTasks.pop();
+ } else {
+ rawTask = new RawTask();
+ }
+ rawTask.task = task;
+ rawAsap(rawTask);
+}
+
+// We wrap tasks with recyclable task objects. A task object implements
+// `call`, just like a function.
+function RawTask() {
+ this.task = null;
+}
+
+// The sole purpose of wrapping the task is to catch the exception and recycle
+// the task object after its single use.
+RawTask.prototype.call = function () {
+ try {
+ this.task.call();
+ } catch (error) {
+ if (asap.onerror) {
+ // This hook exists purely for testing purposes.
+ // Its name will be periodically randomized to break any code that
+ // depends on its existence.
+ asap.onerror(error);
+ } else {
+ // In a web browser, exceptions are not fatal. However, to avoid
+ // slowing down the queue of pending tasks, we rethrow the error in a
+ // lower priority turn.
+ pendingErrors.push(error);
+ requestErrorThrow();
+ }
+ } finally {
+ this.task = null;
+ freeTasks[freeTasks.length] = this;
+ }
+};
Code Review / simantics / district.git / blobdiff