---
name: VPP Comms Library (VCL)
maintainer: Florin Coras <fcoras@cisco.com>
features:
  - Abstracts vpp host stack sessions to integer session handles
  - Exposes its own async communication functions, i.e., epoll, select, poll
  - Supports multi-worker applications
  - Sessions cannot be shared between multiple threads/processes
  - VCL Locked Sessions (VLS):
      - Ensure through locking that only one thread accesses a session at a
        time
      - Detects and registers forked processes as new VCL workers. It does not
        register threads as new workers.
  - LD_PRELOAD shim (LDP):
      - Intercepts syscalls and injects them into VLS.
      - Applications that are supported work with VCL and implicitly with VPP's
        host stack without any code change
      - It does not support all syscalls and syscall options
description: "VCL simplifies app interaction with session layer by exposing
              APIs that are similar to but not POSIX-compliant."
state: production
properties: [API, CLI, MULTITHREAD]