Critical Sections

• A region of code

• Must only be executed by one thread at a time

• Usually when accessing a shared resource

  • Shared data, network connection, hardware device

• The thread "enters" the critical section

  • It starts executing the code in the critical section

• The thread "leaves" the critical section

  • It has executed all the code in the critical section

Single track Railway

• The track can only be used by one train at a time
• When a train approaches this section of track:
  • If there is another train in the section, wait
  • Proceed only when there is no other train

Locking Protocol

• One thread can enter the critical section

  • All the other threads are "locked out"
  • Only this thread can execute the code in the critical section

• The thread leaves the critical section

  • One of the other threads can now enter it