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'use strict';
const {
// For easy access to the nextTick state in the C++ land,
// and to avoid unnecessary calls into JS land.
tickInfo,
// Used to run V8's micro task queue.
runMicrotasks,
setTickCallback,
initializePromiseRejectCallback
} = internalBinding('task_queue');
const {
setHasRejectionToWarn,
hasRejectionToWarn,
promiseRejectHandler,
emitPromiseRejectionWarnings
} = require('internal/process/promises');
const {
getDefaultTriggerAsyncId,
newAsyncId,
initHooksExist,
destroyHooksExist,
emitInit,
emitBefore,
emitAfter,
emitDestroy,
symbols: { async_id_symbol, trigger_async_id_symbol }
} = require('internal/async_hooks');
const { ERR_INVALID_CALLBACK } = require('internal/errors').codes;
const FixedQueue = require('internal/fixed_queue');
// *Must* match Environment::TickInfo::Fields in src/env.h.
const kHasTickScheduled = 0;
function hasTickScheduled() {
return tickInfo[kHasTickScheduled] === 1;
}
function setHasTickScheduled(value) {
tickInfo[kHasTickScheduled] = value ? 1 : 0;
}
const queue = new FixedQueue();
function runNextTicks() {
if (!hasTickScheduled() && !hasRejectionToWarn())
runMicrotasks();
if (!hasTickScheduled() && !hasRejectionToWarn())
return;
internalTickCallback();
}
function internalTickCallback() {
let tock;
do {
while (tock = queue.shift()) {
const asyncId = tock[async_id_symbol];
emitBefore(asyncId, tock[trigger_async_id_symbol]);
// emitDestroy() places the async_id_symbol into an asynchronous queue
// that calls the destroy callback in the future. It's called before
// calling tock.callback so destroy will be called even if the callback
// throws an exception that is handled by 'uncaughtException' or a
// domain.
// TODO(trevnorris): This is a bit of a hack. It relies on the fact
// that nextTick() doesn't allow the event loop to proceed, but if
// any async hooks are enabled during the callback's execution then
// this tock's after hook will be called, but not its destroy hook.
if (destroyHooksExist())
emitDestroy(asyncId);
const callback = tock.callback;
if (tock.args === undefined)
callback();
else
Reflect.apply(callback, undefined, tock.args);
emitAfter(asyncId);
}
setHasTickScheduled(false);
runMicrotasks();
} while (!queue.isEmpty() || emitPromiseRejectionWarnings());
setHasRejectionToWarn(false);
}
class TickObject {
constructor(callback, args, triggerAsyncId) {
// This must be set to null first to avoid function tracking
// on the hidden class, revisit in V8 versions after 6.2
this.callback = null;
this.callback = callback;
this.args = args;
const asyncId = newAsyncId();
this[async_id_symbol] = asyncId;
this[trigger_async_id_symbol] = triggerAsyncId;
if (initHooksExist()) {
emitInit(asyncId,
'TickObject',
triggerAsyncId,
this);
}
}
}
// `nextTick()` will not enqueue any callback when the process is about to
// exit since the callback would not have a chance to be executed.
function nextTick(callback) {
if (typeof callback !== 'function')
throw new ERR_INVALID_CALLBACK();
if (process._exiting)
return;
var args;
switch (arguments.length) {
case 1: break;
case 2: args = [arguments[1]]; break;
case 3: args = [arguments[1], arguments[2]]; break;
case 4: args = [arguments[1], arguments[2], arguments[3]]; break;
default:
args = new Array(arguments.length - 1);
for (var i = 1; i < arguments.length; i++)
args[i - 1] = arguments[i];
}
if (queue.isEmpty())
setHasTickScheduled(true);
queue.push(new TickObject(callback, args, getDefaultTriggerAsyncId()));
}
// TODO(joyeecheung): make this a factory class so that node.js can
// control the side effects caused by the initializers.
exports.setup = function() {
// Initializes the per-isolate promise rejection callback which
// will call the handler being passed into this function.
initializePromiseRejectCallback(promiseRejectHandler);
// Sets the callback to be run in every tick.
setTickCallback(internalTickCallback);
return {
nextTick,
runNextTicks
};
};
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