Blocking System Calls in KRoC/Linux

This paper describes an extension to Kent Retargetable occam Compiler (KRoC), which enables the execution of a blocking call, without blocking the occam-kernel. This allows a process to make a blocking system call (eg, read, write), without blocking processes running in parallel with it. Blocking calls are implemented using Linux clones which communicate using shared memory, and synchronise using kernel level semaphores. The usefulness of this is apparent in server applications with a need to handle multiple clients simultaneously. An implementation of an occam web-server is described in section 5, which uses standard TCP sockets via an occam socket library. The web-server comes with the ability to execute CGI scripts as well as dispensing static pages, which demonstrates some level of OS process management from within occam. However, this mechanism is not limited to blocking in the Linux kernel. On multi- processor machines, the clones are quite free to be scheduled on different processors, allowing computationally heavy processing to be performed aside the occam world, but still with a reasonable level of interaction with it. Using them in this way provides a coarse-grained level of parallelism from within the fine-grained occam world.