Other Supports from ISA

• Some processors support TestAndSet instruction.
  boolean TestAndSet(boolean *mem) {
  boolean ret = *mem;
  *mem = TRUE;
  return ret;
  }
• Acquire Lock:
  while TestAndSet(&lock) ;
• Release Lock:
  lock = false;

Support From The OS

• If OS is non-preemptive
  • System calls can be provided for
    • Acquire Lock and Release Lock.
  • Process can not be preempted while acquiring and releasing locks.
• If OS is preemptive.
  • System calls are tricky to support but not impossible.