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Editorial Team
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Asked: 2026-05-12T12:25:12+00:00

All UIWebViews share a single web thread. When one of them is init -ed,

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All UIWebViews share a single web thread.

When one of them is init-ed, removed from superview etc., they will attempt to lock the web thread from the main thread in a blocking fashion, thus temporarily freezing the run loop of the main thread.

If the web thread is busy, e.g. while doing a long synchronous XMLHttpRequest, this may block the main thread for a long time.

Is there a way to avoid this?

If I could modify UIWebView, I’d just make the lock attempt non-blocking, but obviously that’s not the case, so I’m looking for other clever ideas.

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1 Answer

  1. Editorial Team

    The long and short of it is: avoid doing anything that blocks the web thread for a significant amount of time (window.alert, window.prompt, XMLHttpRequest.open('GET', url, false), possibly others)

    Also, avoid calling methods that lock the web thread and then immediately doing something that takes a long time as the web thread is only unlocked once control is returned to the run loop. (Example: call -[UITextView setText:] then read a file synchronously on the main thread)

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