Shell2: 200x Faster, Persistent, and Multiplayer-Native Shell

Terminals have evolved from the physical TTYs of the past to today's PTY (Pseudo-TTY) approach, which enables remote control over a network.

Replit leverages PTY for its browser-based remote development environment, where the pid1 process inside the container previously handled requests. To reduce the overhead of this process and increase development speed, Replit introduced pid2, a next-generation process.

Shell2 maximizes performance through the following technical improvements:

• Eliminating string-byte conversion: Boosted performance by directly handling raw bytes without UTF-8 encoding conversion.
• Avoiding stdio: Designed so that conman passes the WebSocket file descriptor directly to pid2, instead of relaying commands through a stdio pipe.
• Preventing protocol introspection: Removed unnecessary computation by using raw byte-for-byte copying instead of unmarshaling data into structs.
• Zero-overhead principle: Optimized baseline performance by reducing unnecessary backpressure handling and complex channel/select calls.

Through these changes, Replit delivers a much faster and smoother Shell experience than before.