Message Passing and Locks
Message passing can be used as a way of controlling access to resources in a concurrent or asynchronous system. One of the main alternatives is mutual exclusion or locking. Examples of resources include shared memory, a disk file or region thereof, a database table or set of rows.
In locking, a resource is essentially shared, and processes wishing to access it (or a sector of it) must first obtain a lock. Once the lock is acquired, other processes are blocked out, ensuring that corruption from simultaneous writes does not occur. After the process with the lock is finished with the resource, the lock is then released.
With the message-passing solution, it is assumed that the resource is not exposed, and all changes to it are made by an associated process, so that the resource is encapsulated. Processes wishing to access the resource send a request message to the handler. If the resource (or subsection) is available, the handler makes the requested change as an atomic event, that is conflicting requests are not acted on until the first request has been completed. If the resource is not available, the request is generally queued. The sending programme may or may not wait until the request has been completed.
Read more about this topic: Message Passing
Famous quotes containing the words message, passing and/or locks:
“Gossip, then, is content, a message about people; rumor is a process. It takes a bit of gossip and reshapes it, modifies it in some way, and passes it along from individual to individual in different ways.”
—Jack Levin (b. 1941)
“The little toy dog is covered with dust,
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And the little toy soldier is red with rust,
And the musket moulds in his hands.
Time was when the little toy dog was new,
And the soldier was passing fair;
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Kissed them and put them there.”
—Eugene Field (1850–1895)
“Nodding, its great head rattling like a gourd,
And locks like seaweed strung on the stinking stone,
The nightmare stumbles past,”
—Robert Penn Warren (1905–1989)