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First, B gets the access to the section. Once B finishes writing the value, A gets the access to the critical section, and variable x can be read. By carefully controlling which variables are modified inside and outside the critical section, concurrent access to the shared variable are prevented.
The process attempts to enter the critical section. Critical Section The process is allowed to access the shared resource in this section. Exit The process leaves the critical section and makes the shared resource available to other processes. If a process wishes to enter the critical section, it must first execute the trying section and wait ...
Suppose we have a shared memory area (critical section) with the basic constraints detailed above. It is possible to protect the shared data behind a mutual exclusion mutex, in which case no two threads can access the data at the same time.
Processes' access to critical section is controlled by using synchronization techniques. When one thread starts executing the critical section (serialized segment of the program) the other thread should wait until the first thread finishes.
Some systems also implement mandatory locks, where attempting unauthorized access to a locked resource will force an exception in the entity attempting to make the access. The simplest type of lock is a binary semaphore. It provides exclusive access to the locked data. Other schemes also provide shared access for reading data.
The algorithm uses two variables: flag and turn.A flag[n] value of true indicates that the process n wants to enter the critical section.Entrance to the critical section is granted for process P0 if P1 does not want to enter its critical section or if P1 has given priority to P0 by setting turn to 0.
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The critical section is that part of code that requires exclusive access to resources and may only be executed by one thread at a time. In the bakery analogy, it is when the customer trades with the baker that others must wait. When a thread wants to enter the critical section, it has to check whether now is its turn to do so.