Synchronisation

Race condition

A situation where multiple threads may manipulate data in such a way that the outcome depends on the execution order.

Critical Section

A section of code that manipulates shared data.

Mutual Exclusion

Making sure that only one thread can be executing in a critical section at once.

Deadlock

When two or more processes are waiting for something that can only be provided by one of the waiting processes.

Semaphores

• Two operations on a shared value:

  P(s)

  while (s <= 0) {}
  s--;

  V(s)

  s++;

• Don’t busy wait; give up the cpu.

Java

wait()

Give up the lock, and yield to another thread, waiting for something to call notify.

notify()

Yield to a waiting thread.

notifyAll()

Wake up all waiting threads.