ISO: International Standard ISO/IEC 8652:1995(E), Ada Reference Manual, Intermetrics, Inc., 1995.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....the approach of providing network application support; section 8 highlights some interesting implementation details, and section 9 finally describes an additional extension to the basic network client support. 2 The Ada 95 Distributed Programming Model The Ada 95 Reference Manual Annex E [2] defines a precise model for programming distributed systems. A distributed application is viewed as a set of virtual nodes called partitions which represent the unit of distribution. Each partition can hold a collection of library units or packages and may provide an interface towards other ....

....network client partitions as such. 12 Conformance with the Ada 95 Reference Manual, Annex Diploma Thesis Jrg Kienzle 6 Conformance with the Ada 95 Reference Manual, Annex E The Ada 95 language has been completely defined and standardized by the ISO organization in the Ada 95 Reference Manual [2]. Compilers even have to be validated against this standard. This makes it very important to verify that the idea of network application support and the resulting restriction do not violate or conflict in any way with the standard. The important section of the Ada 95 Reference Manual is Annex E, ....

ISO: International Standard ISO/IEC 8652:1995(E), Ada Reference Manual, Intermetrics, Inc., 1995.

....from and to the storage device. What kind of value types they must support will not be discussed in detail here but we can consider that those operations work with stream elements, generated at a higher level by a serialization mechanism. Some object oriented programming languages, for example Ada [1] or Java [5.13] have such a mechanism as a predefined implementation for all value types. OBJECT ORIENTED STABLE STORAGE DIPLOMA THESIS OF X AVIER CARON, EPFL, 2000. PAGE 9 62 Volatile Storage Type Non Stable Storage Type Non Volatile Storage Type Open( Close( Delete( ....

....the process using the storage, a server that will be used to locate remote storages and a process running on the remote machine where the physical storage resides. All three processes communicate using the features described in the Distributed Systems Annex of the Ada 95 Reference Manual [1]. 3.1 ADA DISTRIBUTED SYSTEMS ANNEX GLADE In this section, we will first present a brief overview of the DSA and the implementation of the DSA for the GNAT compiler that we are going to use. Next, we will present the design of the storage. 3.1.1 FEATURES OF THE DSA The Annex E of the Ada 95 ....

ISO: International Standard ISO/IEC 8652:1995(E): Ada Reference Manual, Lecture Notes in Computer Science 1246, Springer Verlag, 1997; ISO, 1995.

....how the network application support has been integrated into the GLADE environment; section 9 finally describes an additional extension to the basic network client support and the last section draws some conclusions. 2 The Ada 95 Distributed Systems Model The Ada 95 Reference Manual Annex E [1] defines a precise model for programming distributed systems. A distributed application is viewed as a set of virtual nodes called partitions which represent the unit of distribution. Each partition can hold a collection of library units or packages and may provide an interface towards other ....

....The Ada Reference Manual only specifies the interface to the PCS. The distributed programming model of Ada 95 was designed with the objective to maintain the properties of a single Ada program, but allowing distributed execution with minimal additional semantic and implementation complexity ([1] E(1) 2] E.1) 3 Network Application Support A minimal network application is comprised of at least one server, typically some kind of database, and any number of identical clients accessing it (see figure 1) In most applications, the central server is running permanently, whereas the clients ....

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ISO: International Standard ISO/IEC 8652:1995(E): Ada Reference Manual, Intermetrics, Inc.

....of the PCS flexible enough to support these characteristics. The rest of this paper will detail our extension of the PCS to provide flexible and totally transparent encryption on links. 5 GARLIC GARLIC [7] is an implementation of the PCS as specified by annex E of the Ada Reference Manual [4] for the GNAT compiler. It implements and encapsulates the protocols needed to provide the semantics of remote procedure calls. Simultaneous RPCs (i.e. from different tasks) are possible, and the called node also can handle RPCs in parallel: for each RPC request, a task is started. GARLIC itself ....

ISO: International Standard ISO/IEC 8652:1995(E), Ada Reference Manual, Intermetrics, Inc., 1995.

....on RAPIDS current state. 2 The System Model A distributed application in Ada 95 is composed of a set of virtual nodes (called partitions ) that themselves are indivisible as far as distribution is concerned and that execute on various physical nodes (computers) which may be heterogeneous [ISO95, E(6) The physical nodes are connected by a network, over which they communicate with each other. A partition in Ada 95 is a collection of library units, some of which constitute its interface towards the other partitions of the application. These well defined interfaces are given by the ....

....semantic checks to ensure the integrity of the distributed application, just like for local subprogram calls. The run time support implements the message protocols underlying the RPC abstraction transparently in its Partition Communication Subsystem (PCS) The language standard strongly suggests [ISO95, E.5(24,25,28) that a partition should handle incoming RPCs concurrently, each one in its own task. 3 Given this model defined by the language standard, we examine transparent replication for fault tolerance assuming an asynchronous heterogeneous distributed system. The partitions of ....

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ISO: International Standard ISO/IEC 8652:1995(E): Ada Reference Manual, Lecture Notes in Computer Science 1246, Springer Verlag, 1997; ISO, 1995.

....only in an implementation permission clause: An implementation may allow separate copies of a partition to be configured on different processing nodes, and to provide appropriate interactions between the copies to present a consistent state of the partition to other active partitions. ISO95, E.1(12) With this statement, the standard argues in favor of a transparent solution to replication: as a distributed application is configured only after it has been programmed and compiled, it follows that the intent is that replication should be offered in a way transparent to the replicas ....

....in Ada 95 is needed. The piecewise deterministic computation model [SY85, Eln93] views an execution as a sequence of deterministic state intervals that are separated by non deterministically occurring events. This model can be applied to Ada 95 as well. The signaling model of the language [ISO95, 9.10(3 10) guarantees that all accesses to objects shared between any two tasks actually happen in some sequential order. As a result, shared objects must be protected using appropriate application level synchronization through protected objects or rendezvous 1 . A partition is considered ....

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ISO: International Standard ISO/IEC 8652:1995(E): Ada Reference Manual, Lecture Notes in Computer Science 1246, Springer Verlag, 1997; ISO, 1995.

....re execution of a request after a node failure will lead to the same sequence of state changes. For this reason we require (for the time being) that a replicated Ada partition be deterministic. Currently, this is achieved through the pragmas defined in the Real Time Annex of the Ada 95 standard [5] that provide the means to force deterministic behavior, plus the requirement that a partition that is to be replicated use no timed entry calls 2 . Under the assumption that replicated partitions are deterministic, i.e. that they are state machines in the sense of [11] both active and ....

....that the state of a replicated partition must be encapsulated in packages marked by a special pragma Replicated. While also not completely transparent to the application, such an approach fits well into the model for programming distributed applications defined in annex E of the language standard [5], where interface packages of a partition must be marked by certain pragmas. A Replicated package in a non replicated partition behaves exactly like a normal package. But if the partition is replicated in the configuration phase, the compiler can easily recognize such packages and generate ....

ISO: International Standard ISO/IEC 8652:1995(E): Ada Reference Manual, Intermetrics, Inc. 1995

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