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DocumentationHSLReferenceClassHH\Lib\Async\BasePoll

HH\Lib\Async\BasePoll

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This is available as Async\BasePoll in the www repository.

Asynchronous equivalent of mechanisms such as epoll(), poll() and select()

Read the warnings here first, then see the Poll and KeyedPoll instantiable subclasses.

Transforms a set of Awaitables to an asynchronous iterator that produces results of these Awaitables as soon as they are ready. The order of results is not guaranteed in any way. New Awaitables can be added to the Poll while it is being iterated.

This mechanism has two primary use cases:

  1. Speculatively issuing non-CPU-intensive requests to different backends with very high processing latency, waiting for the first satisfying result and ignoring all remaining requests.

    Example: cross-DC memcache requests

  2. Processing relatively small number of high level results in the order of completion and flushing the output to the user.

    Example: pagelets, multiple GraphQL queries, streamable GraphQL queries

===== WARNING ===== WARNING ===== WARNING ===== WARNING ===== WARNING =====

This is a very heavy-weight mechanism with non-trivial CPU cost. NEVER use this in the following situations:

  1. Waiting for the first available result and ignoring the rest of work, unless the processing latency is extremely high (10ms or more) and the CPU cost of ignored work is negligible. Note: the ignored work will still be computed and will delay your processing anyway if it's CPU costly.

  2. Reordering huge amount of intermediary results. This is currently known to be CPU-intensive.

===== WARNING ===== WARNING ===== WARNING ===== WARNING ===== WARNING =====

Interface Synopsis

namespace HH\Lib\Async;

abstract class BasePoll {...}

Public Methods

Protected Methods