Fix race condition in rake parse:topgems#3648
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`block.call(queue.shift) until queue.empty?` isn't thread safe. If there is one element left in the queue, two or more thread may see `queue.empty?` return `false` and call the blocking `shift` ending in a deadlock. The proper way to synchronize threads with a queue is to close the queue once no more elements need to be added. This should fix the occasional `fatal: No live threads left. Deadlock? (fatal)` failures on CI.
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block.call(queue.shift) until queue.empty?isn't thread safe.If there is one element left in the queue, two or more thread may see
queue.empty?returnfalseand call the blockingshiftending in a deadlock.The proper way to synchronize threads with a queue is to close the queue once no more elements need to be added.
This should fix the occasional
fatal: No live threads left. Deadlock? (fatal)failures on CI. e.g. https://github.com/ruby/prism/actions/runs/17697479732/job/50298732002?pr=3644#step:5:43