Runtime Clients

Runtime Clients

A user can partition their application into multiple STM clients. Every STM client resides in a separate OS process and links to the shared library libstm runtime.so. Clients register resources and runnables with the libstm runtime.so, which creates a mapping between runnable/resource names and their process local addresses - function pointers for runnables and resource pointers (ex. CUDA streams) for resources. After the registration phase, clients then yield to libstm runtime.so by calling stmEnterScheduler(). This function enters an infinite loop that schedules a process runnables via the previously registered function pointers periodically until termination. To exit, clients can either pre-specify a maximum number of hyperepoch frames to execute as a parameter to stm master, or they can call stmExitScheduler() from within the application. For example, the application’s SIGINT or SIGTERM handler might call stmExitScheduler() to gracefully exit from the blocking stmEnterScheduler() call. STM clients follow the following initialization sequence:

• An external entity (the init system) starts the STM Master and all clients. STM does not require that the master and clients be started in any order.
• The STM Master will load and verify the schedule that was passed to it as a command line argument.
• Each client will initialize and register with the STM master. They each follow the following process:
  • Once the client enters its main function, it performs any private initialization (e.g. allocating memory and loading configuration files.)
  • The client initializes its STM client by calling stmClientInit().
  • The client registers each of its runnables with STM by calling stmRegisterCpuRunnable(), stmRegisterCudaSubmitter(), and stmRegisterVpuSubmitter().
  • If the client created references to hardware resources that STM interacts with (e.g., CUDAstreams) it registers those resources with STM by calling stmRegisterCudaResource() and stmRegisterVpuResource().
  • Finally, the client calls stmEnterScheduler(). This hands over control to STM. After this call, the client may not allocate memory or new resources. This call will not return until the system is shut down.
• STM begins executing runnables according to the schedule.