X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/2095c5547acacede3a192a7fd08155cfac713aeb..ac90ceb451c8d228a7de1a9a9cc3821b2cc8b09a:/cruft/doc/overview.xml diff --git a/cruft/doc/overview.xml b/cruft/doc/overview.xml deleted file mode 100644 index 2f757b3488..0000000000 --- a/cruft/doc/overview.xml +++ /dev/null @@ -1,109 +0,0 @@ - - -Overview -3 -GRAS Library - - - -OverviewOverview on the GRAS library - - - -Introduction -This document introduce the GRAS library (Grid Reality And - Simulation, or according to my english dictionary, - Generally Recognized As Safe ;). - -Here are the problems when you want to do so: - - - Communication in SG is done by passing tasks, while in - RL, you have to deal with sockets (or any wrapper to it). - - In RL, each process should provide a main() - function, and it's obviously not the case in SG. - - - - - - - Application class target - If you want to run your code both in RL and in SG, you won't be - able to use the full set of features offered by any of those two - worlds. GRAS tries to provide a suffisent set of features to develop - your application, and implement them in both worlds. - - GRAS uses the paradigm of event-driven - programming, which is an extension to the message-passing - one. Any process of a typical event-driven application declares - callback to incoming events, which can be messages from other - processes, timers or others. - - All messages have an header, specifying its type, and attached - data, represented as one or several C structures. In order to send the - data over the network in RL, a type-description mecanism is provided, and - the RL version of GRAS implements XDR functionnalities. That is to say - that the data are converted to a intermediate representation before being - sent. A possible extension would be to use CDR, where data are sent in - the native format of the sender host, and converted on the destination - host only if needed, but this is still to do. - - In order to not reimplement the wheel, GRAS use existing code, and - adapt them to make them work together. The SG version naturally use the - SimGrid toolkit, while the RL version is based over the communication - library used in NWSOnly the actual sending/receiving - features and formattypes features were taken from NWS. GRAS messaging - stuff is quite different from the NWS one, which was not easily adaptable - in SG as is.. That's why we will now present the NWS - project in order to give you a better understanding of its internals used - here. - - - - The Network Weather Service and its "portability" library - - The purpose of the NWS project is to provide any kind of usefull - information about the availability of a Grid platform. like the CPU load, - free memory and disk of all hosts, the bandwidth and latency between each - host pair, and so on. It is also able to predict the future trend of each - value by applying some statistical treatement to the measurements. - - In order to achieve this goal, the NWS system is composed of four - kind of processes: - - Sensors: those process are in charge or realizing the - actual measurement needed by the system. - - Memory servers: they store on disk the result of the experiments - conducted by the sensors for a later use. - - Forecasters: when a client application asks to, the - forecasters retrieves the measurements from the memory servers, apply - the needed statistical treatement, and then inform the client of the - predicted variations. - - NameServer: Every process in the NWS system have to - register itself to the nameserver, so that any process looks for another - element, it can find the answer by asking to the nameserver. - - - As you can see, this system is distributed by nature, and its - authors builded a specific toolbox they call the portability library. It - contains a great quantity of cool stuff to do various kind of things. The - main part is a very high level messaging library, where processes declare - callbacks to strongly typed messages sent from other processes. - - One of the limitation of this system is that even if processes can - ear to several sockets, all messages received from the different sources - are mixed together and handled by the same control loop. GRAS inherit - this limitation, but in fact, we don't think that it's really limitating, - thanks to the fact that messages are strongly typed. - - The philosophy of this library constitues the heart of GRAS, which - actually provide the same kind of features. - - - -