Condition variables

1
Condition variables
2

• proc notify (cvar)
• acquire (tt_lock)
• for (i 0 to N-1) do
• if (ttablei.cvar cvar
• ttablei.state WAITING)
• ttablei.state ? RUNNABLE
• release(tt_lock)

3

• proc wait(cvar, lock)
• acquire(tt_lock)
• ttableid.lock ? lock
• ttableid.cvar ? cvar
• release(tt_lock)
• yield(WAITING)
• acquire(lock)

4
Implementing condition variables

• proc wait(cvar, lock)
• yield_wait(cval,lock)
• acquire(lock)

5
Implementing condition variables

• proc yield_wait(cvar, lock)
• disable_interrupts
• acquire(tt_lock)
• release(lock)
• ttableid.lock ? lock
• ttableid.cvar ? cvar
• ttableid.sp ? SP
• ttableid.state ? WAITING
• // other yield code
• release(tt_lock)
• enable_interrupts