The above mentioned methods don't handle exceptions correctly in the lambda functions run in the threadpool. The exceptions are swallowed by the threadpool and the RPC ends up blocking forever since the future is never satisfied. For enqueueRecv we should have a try-catch block around it and return MessageType::Exception. For enqueuSend, we can pass the future into the lambda, have a try-catch block, catch an exception and mark the future completed with MessageType::Exception.

cc @ezyang @gchanan @zou3519 @jerryzh168 @pietern @mrshenli @pritamdamania87 @zhaojuanmao @satgera @gqchen @aazzolini @rohan-varma @xush6528