Processes Synchronisation

Process Synchronization!
• Background!
• The Critical-Section Problem!
• Synchronisation Hardware!
• Semaphores!
• Classical Problems of Synchronization!
• Critical Regions!
• Monitors!
• Synchronization in Solaris 2!
• Atomic Transactions!


Background!
• Concurrent access to shared data may result in data inconsistency.!
• Maintaining data consistency requires mechanisms to ensure the orderly execution of cooperating processes.!
• Shared-memory solution to bounded-buffer problem (Chapter 4) allows at most n – 1 items in buffer at the same time. A solution, where all N buffers are used is not simple.!
– Suppose that we modify the producer-consumer code by adding a variable counter, initialized to 0 and incremented each time a new item is added to the buffer

The Critical-Section Problem!
• n processes all competing to use some shared data!
• Each process has a code segment, called critical section, in which the shared data is accessed.!
• Problem – ensure that when one process is executing in its critical section, no other process is allowed to execute in its critical section.!