idea: Joining multiple threads safely

[shirok]

Recent fix in pmap brought attention to this issue.

It is a common pattern that you start multiple worker threads, and later join them all. If one of thread-join! throws an error and we don't handle it, the remaining threads are left unjonied.

So the good way is to always catch exceptions and record them from thread-join! while iterating the list of worker threads, and once all are joined, handle the recorded exceptions. We can make that pattarn an API, say, thread-join-all!.

There are several possibilities regarding how to handle the caught exceptions.

• thread-join-all! returns a list of results, and replace the thrown condition in place of the result.
• Reraise any one of them after all threads are joined.
• Reraise a compond condition of all of caught exceptions.
• Call a callback.