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:
“If you have a message you want to send to hell, give it to me; I’ll carry it!”
—Administration in the State of Sout, U.S. public relief program (1935-1943)
“We all end up living secret lives. We create what we are willing to admire and admiring what we shouldn’t confess to the secret of our own sin, our own insufficiency, our own sadness. We all end up taking our secrets into the world and handing them over to strangers, only to realize it’s often too late to claim them back. The very nature of time passing is sad beyond words. Memories mean they’re gone.”
—Alexander Theroux (b. 1940)
“Many a kiss, both odd and even;
Many a glance, too, has been sent
From out the eye, love’s firmament;
Many a jest told of the keys betraying
This night, and locks picked; yet we’re not a-Maying!”
—Robert Herrick (1591–1674)