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101 lines
4.0 KiB
101 lines
4.0 KiB
"use strict"; |
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var domain; // The domain module is executed on demand |
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var hasSetImmediate = typeof setImmediate === "function"; |
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// Use the fastest means possible to execute a task in its own turn, with |
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// priority over other events including network IO events in Node.js. |
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// |
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// An exception thrown by a task will permanently interrupt the processing of |
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// subsequent tasks. The higher level `asap` function ensures that if an |
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// exception is thrown by a task, that the task queue will continue flushing as |
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// soon as possible, but if you use `rawAsap` directly, you are responsible to |
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// either ensure that no exceptions are thrown from your task, or to manually |
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// call `rawAsap.requestFlush` if an exception is thrown. |
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module.exports = rawAsap; |
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function rawAsap(task) { |
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if (!queue.length) { |
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requestFlush(); |
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flushing = true; |
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} |
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// Avoids a function call |
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queue[queue.length] = task; |
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} |
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var queue = []; |
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// Once a flush has been requested, no further calls to `requestFlush` are |
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// necessary until the next `flush` completes. |
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var flushing = false; |
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// The position of the next task to execute in the task queue. This is |
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// preserved between calls to `flush` so that it can be resumed if |
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// a task throws an exception. |
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var index = 0; |
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// If a task schedules additional tasks recursively, the task queue can grow |
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// unbounded. To prevent memory excaustion, the task queue will periodically |
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// truncate already-completed tasks. |
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var capacity = 1024; |
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// The flush function processes all tasks that have been scheduled with |
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// `rawAsap` unless and until one of those tasks throws an exception. |
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// If a task throws an exception, `flush` ensures that its state will remain |
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// consistent and will resume where it left off when called again. |
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// However, `flush` does not make any arrangements to be called again if an |
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// exception is thrown. |
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function flush() { |
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while (index < queue.length) { |
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var currentIndex = index; |
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// Advance the index before calling the task. This ensures that we will |
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// begin flushing on the next task the task throws an error. |
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index = index + 1; |
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queue[currentIndex].call(); |
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// Prevent leaking memory for long chains of recursive calls to `asap`. |
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// If we call `asap` within tasks scheduled by `asap`, the queue will |
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// grow, but to avoid an O(n) walk for every task we execute, we don't |
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// shift tasks off the queue after they have been executed. |
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// Instead, we periodically shift 1024 tasks off the queue. |
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if (index > capacity) { |
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// Manually shift all values starting at the index back to the |
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// beginning of the queue. |
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for (var scan = 0, newLength = queue.length - index; scan < newLength; scan++) { |
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queue[scan] = queue[scan + index]; |
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} |
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queue.length -= index; |
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index = 0; |
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} |
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} |
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queue.length = 0; |
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index = 0; |
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flushing = false; |
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} |
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rawAsap.requestFlush = requestFlush; |
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function requestFlush() { |
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// Ensure flushing is not bound to any domain. |
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// It is not sufficient to exit the domain, because domains exist on a stack. |
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// To execute code outside of any domain, the following dance is necessary. |
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var parentDomain = process.domain; |
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if (parentDomain) { |
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if (!domain) { |
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// Lazy execute the domain module. |
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// Only employed if the user elects to use domains. |
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domain = require("domain"); |
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} |
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domain.active = process.domain = null; |
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} |
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// `setImmediate` is slower that `process.nextTick`, but `process.nextTick` |
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// cannot handle recursion. |
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// `requestFlush` will only be called recursively from `asap.js`, to resume |
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// flushing after an error is thrown into a domain. |
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// Conveniently, `setImmediate` was introduced in the same version |
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// `process.nextTick` started throwing recursion errors. |
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if (flushing && hasSetImmediate) { |
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setImmediate(flush); |
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} else { |
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process.nextTick(flush); |
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} |
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if (parentDomain) { |
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domain.active = process.domain = parentDomain; |
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} |
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}
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