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Ada Tasking Error


a name for an exception. The name of an exception can only be used in raise statements, exception handlers, and renaming declarations. exception_declaration ::= identifier_list : exception;

Ada Constraint_error

An exception declaration with several identifiers is equivalent to a sequence of ada storage error single exception declarations, as explained in section 3.2. Each single exception declaration declares a name for a

Exception Handling In Ada

different exception. In particular, if a generic unit includes an exception declaration, the exception declarations implicitly generated by different instantiations of the generic unit refer to distinct exceptions (but ada exception handling example all have the same identifier). The particular exception denoted by an exception name is determined at compilation time and is the same regardless of how many times the exception declaration is elaborated. Hence, if an exception declaration occurs in a recursive subprogram, the exception name denotes the same exception for all invocations of the recursive subprogram. The following ada task terminate exceptions are predefined in the language; they are raised when the situations described are detected. CONSTRAINT_ERROR This exception is raised in any of the following situations: upon an attempt to violate a range constraint, an index constraint, or a discriminant constraint; upon an attempt to use a record component that does not exist for the current discriminant values; and upon an attempt to use a selected component, an indexed component, a slice, or an attribute, of an object designated by an access value, if the object does not exist because the access value is null. NUMERIC_ERROR This exception is raised by the execution of a predefined numeric operation that cannot deliver a correct result (within the declared accuracy for real types); this includes the case where an implementation uses a predefined numeric operation for the execution, evaluation, or elaboration of some construct. The rules given in section 4.5.7 define the cases in which an implementation is not required to raise this exception when such an error situation arises; see also section 11.6. PR

1.3 Guards 2 Protected types 3 Entry families 4 Termination 5 Timeout 6 Conditional entry calls 7 Requeue statements 8 Scheduling 9 Interfaces 10 See also 10.1 Wikibook 10.2 Ada Reference Manual 10.2.1 Ada 95 10.2.2 Ada 2005 11 Ada Quality and Style Guide Tasks[edit]

Ada Task Priority

A task unit is a program unit that is obeyed concurrently with the rest of ada task tutorial an Ada program. The corresponding activity, a new locus of control, is called a task in Ada terminology, and is similar to

Ada Task Type

a thread, for example in Java Threads. The execution of the main program is also a task, the anonymous environment task. A task unit has both a declaration and a body, which is mandatory. A task body may http://archive.adaic.com/standards/83lrm/html/lrm-11-01.html be compiled separately as a subunit, but a task may not be a library unit, nor may it be generic. Every task depends on a master, which is the immediately surrounding declarative region - a block, a subprogram, another task, or a package. The execution of a master does not complete until all its dependent tasks have terminated. The environment task is the master of all other tasks; it terminates only when all other tasks have https://en.wikibooks.org/wiki/Ada_Programming/Tasking terminated. Task units are similar to packages in that a task declaration defines entities exported from the task, whereas its body contains local declarations and statements of the task. A single task is declared as follows: task Single is declarations of exported identifiers end Single; ... task body Single is local declarations and statements end Single; A task declaration can be simplified, if nothing is exported, thus: task No_Exports; Ex. 1 procedure Housekeeping is task Check_CPU; task Backup_Disk; task body Check_CPU is ... end Check_CPU; task body Backup_Disk is ... end Backup_Disk; -- the two tasks are automatically created and begin execution begin -- Housekeeping null; -- Housekeeping waits here for them to terminate end Housekeeping; It is possible to declare task types, thus allowing task units to be created dynamically, and incorporated in data structures: task type T is ... end T; ... Task_1, Task_2 : T; ... task body T is ... end T; Task types are limited, i.e. they are restricted in the same way as limited private types, so assignment and comparison are not allowed. Rendezvous[edit] The only entities that a task may export are entries. An entry looks much like a procedure. It has an identifier and may have in, out or in out parameters. Ada supports communication from task to task by means of the entry call. Information passe

something else. This capability must be available in a computer program also, since a computer program is often used to simulate something in real life. This http://perso.telecom-paristech.fr/~pautet/Ada95/chap28.htm chapter will give examples of impatient programs, those that refuse to simply wait forever for a certain job to be done. THE BASIC PROGRAM OUTLINE Example program ------> e_c28_p1.ada Examine the file named e_c28_p1.ada http://dl.acm.org/citation.cfm?id=892751 for the program that will serve as the outline for the selective rendezvous even though it does not contain one. The program consists of four tasks, one each to describe Bill's day and John's ada task day, and one each to describe eating a meal at a restaurant and at a fast food Burger Boy (hopefully not an actual restaurant). In this program, all of the delay times have been defined in terms of a constant named HOURS which actually causes a delay of one second per hour to speed up program execution to a reasonable level. Eating a meal at the restaurant requires ada tasking error half an hour to be served and another half hour to consume the meal, whereas the Burger Boy requires only one tenth of an hour to be served and another tenth to consume the meal. The task named Bills_Day has him eating three meals only one hour apart, and the task named Johns_Day has him eating two meals in rapid succession then waiting four hours until he eats supper. Another interesting point is the fact that both eat every meal at the restaurant with no concern for how long they have to wait to be seated and eat. It is of no concern either to the Ada program at hand or the analysis of the problem, that one of the tasks is never called, because this is perfectly legal. Finally, both the restaurant and the Burger Boy can only serve one customer at a time, since this is the way the tasks were programmed. They can however, each serve a different customer at the same time. EATING MEALS IS VERY SLOW You will notice, by inspecting the delays, that John waits 0.4 hours and gets to the restaurant first, then takes a total of one hour to eat. Bill waits one hou

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