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Exceptions cannot be captured by default uncaught exception handler

Description

Both core.async thread pools have a try/catch which catches and prints exceptions thrown in callbacks. This prevents application code from using the built-in mechanisms of the JVM to handle exceptions on arbitrary threads, namely Thread.setDefaultUncaughtExceptionHandler

In addition, the pool for 'thread' and 'thread-call' does not close the channel when an exception is thrown, which may lead to deadlocks.

Current Patch: 0002-ASYNC-76-propagate-exceptions-with-tests.patch

Approach: For the callback/go thread pool, do not catch exceptions at all. For the 'thread' pool, remove the 'catch' and close the channel in a 'finally'.

Background: Printing exceptions was added shortly after changing the arity to the 'put!' callback, to aid in debugging, see commit 9fcae995. Prior to this, the 'thread-call' function has always dropped exceptions silently; see commit 0b8e6171.

Duplicate of and similar to ASYNC-61, both of which request that the thread pools dispatch errors to a handler function Var which application code can alter.

An earlier issue (no JIRA ticket) occurred when tasks were submitted to the ThreadPoolExecutor with .submit, which returns a Future, instead of .execute.

Environment

None

Status

Assignee

Stuart Sierra

Reporter

Stuart Sierra

Labels

None

Approval

Ok

Patch

Code and Test

Priority

Major