TimeHandlers Interface

The TimeHandlers interface handles emulation tasks related to timing. These include timeouts, the softclock, mapped time, and performance measurement.

• Timeouts: The timeout mechanism makes use of the SPIN alarm facility. The SPIN alarm facility runs a procedure after a given amount of time. For timeouts, the procedure passed to the alarm interface kicks a timeout semaphore. The code setting the timeout then waits on that semaphore. After the appropriate wait, the alarm goes off, the semaphore is kicked, and the waiting thread continues.
• Softclock: The OSF/1 server softclock is built using the Mach message interface. Since SPIN does not provide the Mach message interface, special system calls are provided to emulate the softclock. The softclock is primarily based on timeouts. A thread drops into the kernel with a timeout value. It will either be restarted by the timeout mechanism, or it will be "poked" by another server thread.
• Mapped Time: The OSF/1 server accesses the current time through a global mapped time variable. The mapped time variable is constructed by using device_map() to map the time device into a kernel memory location and then vm_map() to map that kernel memory location into the server. SPIN supports neither of these mapping features. Hence, a server-created thread periodically accesses the current time through the SAL time interface and writes it to the server address space.
• Measurement: Finally, the TimeHandlers interface provides some basic procedures to time activity in the Mach/OSF/1 emulation modules.

The TimeHandlers interface is TimeHandlers.i3.