Optimize the lifecycle of async requests #765
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Async HTTP request work by emitting a "Progress" object to a callback. This object has a "done" flag which, when `true`, indicates that all data has been emitting and no future "Progress" objects will be sent. Callers like XHR buffer the response and wait for "done = true" to then process the request. The HTTP client relies on two important object pools: the connection and the state (with all the buffers for reading/writing). In its current implementation, the async flow does not release these pooled objects until the final callback has returned. At best, this is inefficient: we're keeping the connection and state objects checked out for longer than they have to be. At worse, it can lead to a deadlock. If the calling code issues a new request when done == true, we'll eventually run out of state objects in the pool. This commit now releases the state objects before emit the final "done" Progress message. For this to work, this final message will always have null data and an empty header object.
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Async HTTP request work by emitting a "Progress" object to a callback. This object has a "done" flag which, when
true, indicates that all data has been emitting and no future "Progress" objects will be sent.Callers like XHR buffer the response and wait for "done = true" to then process the request.
The HTTP client relies on two important object pools: the connection and the state (with all the buffers for reading/writing).
In its current implementation, the async flow does not release these pooled objects until the final callback has returned. At best, this is inefficient: we're keeping the connection and state objects checked out for longer than they have to be. At worse, it can lead to a deadlock. If the calling code issues a new request when done == true, we'll eventually run out of state objects in the pool.
This commit now releases the state objects before emit the final "done" Progress message. For this to work, this final message will always have null data and an empty header object.