Epoch Boundaries

All runnables in an epoch must complete before any runnable in the next epoch can begin. This is implemented via an additional, STM generated client called the framesync client. The framesync client waits on leaf node runnables to signal completion, and then sends a signal to root node runnables to begin executing in the next epoch. Given a schedule overrun, the STM runtime can operate in 2 modes: a frameskip mode and a free-running mode.

• Frameskip Mode In this mode, the framesync client will block the start of the next epoch until the next multiple of the epoch length. For example, if the epoch length is 100ms, and the last runnable in an epoch completes at t=350ms, the next epoch will start at t=400ms. If the epoch length is 100ms and the last runnable in an epoch completes at t=90ms, the next epoch will start at t=100ms.
• No-Frameskip-on-Overrun Mode In this mode, the next epoch will start as soon as all runnables in the previous epoch have finished, if the previous epoch over-ran its scheduled length.