Locks and semaphores in Memo

Memo Prog Tech

• Shared records
• Unordered queues
• Locks and semaphores
• Readers/Writers
  • readers preferred
  • writers preferred
  • taking turns
• Send/Receive
• Ordered Queues
• Barriers
• Job jars / self scheduling
• Implementation
• References

Locks. Naturally, an explicit lock can simply be represented by an empty memo in a folder.

FOLDER_NAME lock;

MEMO q;

...

memo_write(lock,"",0);

...

q = memo_get(lock);

... /* perform critical section */

memo_replace(q);

Semaphores. The simplest implementation of a counting semaphore is identical to a lock, except that to initialize the semaphore, a process places as many empty memos in the semaphore's folder as are required by the initial count.

This page last updated 09/30/97