coherence meaning in computer architecture

Synchronization takes more time than computation, especially in distributed computing. One of the challenges for exascale algorithm design is to minimize or reduce synchronization. This frequent polling robs processing time from other processes.

busy waiting, which occurs when a process frequently polls to determine if it has access to a critical section.

This violation of priority rules can happen under certain circumstances and may lead to serious consequences in real-time systems

priority inversion, which occurs when a high-priority process is in the critical section, and it is interrupted by a medium-priority process.

starvation, which occurs when a process is waiting to enter the critical section, but other processes monopolize the critical section, and the first process is forced to wait indefinitely.

In this case, the processes just keep waiting and execute no further

deadlock, which occurs when many processes are waiting for a shared resource (critical section) which is being held by some other process.

Other than mutual exclusion, synchronization also deals with the following:

In the same way, an ATM will not provide any service until it receives a correct PIN. Similarly, one cannot check e-mails before validating the appropriate credentials (for example, user name and password). For example, one cannot board a plane before buying a ticket. If it is assigned to Process 1, the other process (Process 2) needs to wait until Process 1 frees that resource (as shown in Figure 2).įigure 2: A process accessing a shared resource if available, based on some synchronization technique.Īnother synchronization requirement which needs to be considered is the order in which particular processes or threads should be executed. Hence, when Process 1 and 2 both try to access that resource, it should be assigned to only one process at a time. Synchronization should be used here to avoid any conflicts for accessing this shared resource. All three of them are concurrently executing, and they need to share a common resource (critical section) as shown in Figure 1. If proper synchronization techniques are not applied, it may cause a race condition where the values of variables may be unpredictable and vary depending on the timings of context switches of the processes or threads.įor example, suppose that there are three processes, namely 1, 2, and 3. When one thread starts executing the critical section (serialized segment of the program) the other thread should wait until the first thread finishes. Processes' access to critical section is controlled by using synchronization techniques. Thread synchronization is defined as a mechanism which ensures that two or more concurrent processes or threads do not simultaneously execute some particular program segment known as critical section. Requirements Figure 1: Three processes accessing a shared resource ( critical section) simultaneously. Producer-Consumer: In a producer-consumer relationship, the consumer process is dependent on the producer process until the necessary data has been produced.Įxclusive use resources: When multiple processes are dependent on a resource and they need to access it at the same time, the operating system needs to ensure that only one processor accesses it at a given point in time. Thus, parallel programming requires synchronization as all the parallel processes wait for several other processes to occur. Then, they are joined again and leave the system. After being serviced, each sub-job waits until all other sub-jobs are done processing. Mentioned below are some of the main needs for synchronization:įorks and Joins: When a job arrives at a fork point, it is split into N sub-jobs which are then serviced by n tasks. The need for synchronization does not arise merely in multi-processor systems but for any kind of concurrent processes even in single processor systems. In computer science, synchronization is the task of coordinating multiple of processes to join up or handshake at a certain point, in order to reach an agreement or commit to a certain sequence of action. JSTOR ( November 2014) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed.įind sources: 'Synchronization' computer science – news Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.

Coherence meaning in computer architecture