Attempted to yield to AsyncThrowingStream in terminated state

taylorswift · December 3, 2023, 9:58pm

i’ve encountered a crash in a NIOHTTP2 application; unfortunately the stack dump is pretty thin.

Thread 2 "NIO-ELT-0-#1" crashed:
[inlined] [system] 0x000055bf2287b0d4 Swift runtime failure: precondition failure in UnidocServer at /swift/swift-unidoc/<compiler-generated>
                   0x000055bf2287b0d4 NIOHTTP2AsyncSequence.Continuation.yield(any:) + 372 in UnidocServer at checkouts/swift-nio-http2/Sources/NIOHTTP2/HTTP2CommonInboundStreamMultiplexer.swift:513:21

it looks like it is failing this precondition:

github.com

apple/swift-nio-http2/blob/1.29.0/Sources/NIOHTTP2/HTTP2CommonInboundStreamMultiplexer.swift#L513


      
          ///
          /// It takes channels as as `Any` type to allow wrapping by the stream initializer.
          func yield(any: Any) {
              let yieldResult = self.continuation.yield(any as! Output)
                  switch yieldResult {
                  case .enqueued:
                      break // success, nothing to do
                  case .dropped:
                      preconditionFailure("Attempted to yield when AsyncThrowingStream is over capacity. This shouldn't be possible for an unbounded stream.")
                  case .terminated:
                      preconditionFailure("Attempted to yield to AsyncThrowingStream in terminated state.")
                  default:
                      preconditionFailure("Attempt to yield to AsyncThrowingStream failed for unhandled reason.")
                  }
          }
          
          /// `finish` marks the continuation as finished.
          func finish() {
              self.continuation.finish()
          }

what are some of the reasons i could be encountering this precondition failure, through “normal” use of NIOHTTP2?

lukasa · December 4, 2023, 2:30pm

At first blush this looks like a bug in the cancellation code. I'll see if I can draw up a quick reproducer.

lukasa · December 4, 2023, 2:41pm

Yeah, that's it, I have an easy repro. Will ask one of the team to take a quick look.

taylorswift · February 28, 2024, 5:38pm

if anyone’s arriving here from search, the fix should have shipped in swift-nio-http2 1.30.0