Head-of-Line Blocking¶

When multiple independent streams share an ordered channel, a stall in one stream blocks all subsequent streams, even those unrelated to the stall; eliminating this requires either independent channels or application-level multiplexing with independent stream handling.

Tension Addressed¶

Simplicity vs. Performance

Recognizable As¶

Single-threaded bottlenecks, queue-based processing delays, ordered delivery blocking, HTTP/1.1 pipelining problems

Canonical Sources¶

Belshe et al., RFC 7540 HTTP/2 (2015); Iyengar & Thomson, RFC 9000 QUIC (2021)

Transfers To¶

Concurrent programming (thread pools), message queues (partition strategies), database transactions (lock contention), UI rendering (main thread blocking)