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import { makeRequestCall, makeRequestCallFromTimer } from './makeRequestCall.mjs';
export class AsapQueue {
// Use the fastest means possible to execute a task in its own turn, with
// priority over other events including IO, animation, reflow, and redraw
// events in browsers.
//
// An exception thrown by a task will permanently interrupt the processing of
// subsequent tasks. The higher level `asap` function ensures that if an
// exception is thrown by a task, that the task queue will continue flushing as
// soon as possible, but if you use `rawAsap` directly, you are responsible to
// either ensure that no exceptions are thrown from your task, or to manually
// call `rawAsap.requestFlush` if an exception is thrown.
enqueueTask(task) {
const { queue: q , requestFlush } = this;
if (!q.length) {
requestFlush();
this.flushing = true;
}
// Equivalent to push, but avoids a function call.
q[q.length] = task;
}
constructor(){
this.queue = [];
// 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.
this.pendingErrors = [];
// Once a flush has been requested, no further calls to `requestFlush` are
// necessary until the next `flush` completes.
// @ts-ignore
this.flushing = false;
// The position of the next task to execute in the task queue. This is
// preserved between calls to `flush` so that it can be resumed if
// a task throws an exception.
this.index = 0;
// If a task schedules additional tasks recursively, the task queue can grow
// unbounded. To prevent memory exhaustion, the task queue will periodically
// truncate already-completed tasks.
this.capacity = 1024;
// The flush function processes all tasks that have been scheduled with
// `rawAsap` unless and until one of those tasks throws an exception.
// If a task throws an exception, `flush` ensures that its state will remain
// consistent and will resume where it left off when called again.
// However, `flush` does not make any arrangements to be called again if an
// exception is thrown.
this.flush = ()=>{
const { queue: q } = this;
while(this.index < q.length){
const currentIndex = this.index;
// Advance the index before calling the task. This ensures that we will
// begin flushing on the next task the task throws an error.
this.index++;
q[currentIndex].call();
// Prevent leaking memory for long chains of recursive calls to `asap`.
// If we call `asap` within tasks scheduled by `asap`, the queue will
// grow, but to avoid an O(n) walk for every task we execute, we don't
// shift tasks off the queue after they have been executed.
// Instead, we periodically shift 1024 tasks off the queue.
if (this.index > this.capacity) {
// Manually shift all values starting at the index back to the
// beginning of the queue.
for(let scan = 0, newLength = q.length - this.index; scan < newLength; scan++){
q[scan] = q[scan + this.index];
}
q.length -= this.index;
this.index = 0;
}
}
q.length = 0;
this.index = 0;
this.flushing = false;
};
// 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.
this.registerPendingError = (err)=>{
this.pendingErrors.push(err);
this.requestErrorThrow();
};
// `requestFlush` requests that the high priority event queue be flushed as
// soon as possible.
// This is useful to prevent an error thrown in a task from stalling the event
// queue if the exception handled by Node.js’s
// `process.on("uncaughtException")` or by a domain.
// `requestFlush` is implemented using a strategy based on data collected from
// every available SauceLabs Selenium web driver worker at time of writing.
// https://docs.google.com/spreadsheets/d/1mG-5UYGup5qxGdEMWkhP6BWCz053NUb2E1QoUTU16uA/edit#gid=783724593
this.requestFlush = makeRequestCall(this.flush);
this.requestErrorThrow = makeRequestCallFromTimer(()=>{
// Throw first error
if (this.pendingErrors.length) {
throw this.pendingErrors.shift();
}
});
}
} // The message channel technique was discovered by Malte Ubl and was the
// original foundation for this library.
// http://www.nonblocking.io/2011/06/windownexttick.html
// Safari 6.0.5 (at least) intermittently fails to create message ports on a
// page's first load. Thankfully, this version of Safari supports
// MutationObservers, so we don't need to fall back in that case.
// function makeRequestCallFromMessageChannel(callback) {
// var channel = new MessageChannel();
// channel.port1.onmessage = callback;
// return function requestCall() {
// channel.port2.postMessage(0);
// };
// }
// For reasons explained above, we are also unable to use `setImmediate`
// under any circumstances.
// Even if we were, there is another bug in Internet Explorer 10.
// It is not sufficient to assign `setImmediate` to `requestFlush` because
// `setImmediate` must be called *by name* and therefore must be wrapped in a
// closure.
// Never forget.
// function makeRequestCallFromSetImmediate(callback) {
// return function requestCall() {
// setImmediate(callback);
// };
// }
// Safari 6.0 has a problem where timers will get lost while the user is
// scrolling. This problem does not impact ASAP because Safari 6.0 supports
// mutation observers, so that implementation is used instead.
// However, if we ever elect to use timers in Safari, the prevalent work-around
// is to add a scroll event listener that calls for a flush.
// `setTimeout` does not call the passed callback if the delay is less than
// approximately 7 in web workers in Firefox 8 through 18, and sometimes not
// even then.
// This is for `asap.js` only.
// Its name will be periodically randomized to break any code that depends on
// // its existence.
// rawAsap.makeRequestCallFromTimer = makeRequestCallFromTimer
// ASAP was originally a nextTick shim included in Q. This was factored out
// into this ASAP package. It was later adapted to RSVP which made further
// amendments. These decisions, particularly to marginalize MessageChannel and
// to capture the MutationObserver implementation in a closure, were integrated
// back into ASAP proper.
// https://github.com/tildeio/rsvp.js/blob/cddf7232546a9cf858524b75cde6f9edf72620a7/lib/rsvp/asap.js
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