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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; An exception declaration with several identifiers ada constraint_error is equivalent to a sequence of single exception declarations, as explained in ada storage error section 3.2. Each single exception declaration declares a name for a different exception. In particular, if a generic unit

Exception Handling In Ada

includes an exception declaration, the exception declarations implicitly generated by different instantiations of the generic unit refer to distinct exceptions (but all have the same identifier). The particular exception denoted by an

Ada Exception Handling Example

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 exceptions are predefined in the language; they are raised when the situations described are detected. CONSTRAINT_ERROR This ada task terminate 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. PROGRAM_ERROR This exception is raised upon an attempt to call a subprogram, to activate a task, or to elaborate a generic instantiation, if the body of the corresponding unit has not yet been elaborate

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

Ada Task Priority

Guide Tasks[edit] A task unit is a program unit that is obeyed concurrently with the ada task tutorial rest of an Ada program. The corresponding activity, a new locus of control, is called a task in Ada terminology, and is ada task type similar to 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 http://archive.adaic.com/standards/83lrm/html/lrm-11-01.html task body may 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 https://en.wikibooks.org/wiki/Ada_Programming/Tasking all other tasks have 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 tas

chapter is to instruct you on the use of exceptions, and by the time you complete it, you will have the ability to use exceptions to develop a program http://perso.telecom-paristech.fr/~pautet/Ada95/chap17.htm with its own error handling ability. WHY DO WE NEED EXCEPTIONS? The original charter for the development of Ada included the ability to operate in a real-time environment. You already understand, if you have much http://dl.acm.org/citation.cfm?id=892751 programming experience, that if it is possible for an error to surface, it will eventually surface. Many programming languages simply terminate operation if a "fatal error" is detected, but this could be a disaster if ada task the program was controlling a real-time system upon which human lives or safety depended. A 747 in final approach to the airport, or a system used in a hospital operating room would be two examples of systems that simply could not be terminated abruptly because a bad data point was somehow accumulated. The careful application of Ada exceptions will allow the software to gracefully recover from such a situation rather than ada tasking error aborting operation completely. OUR FIRST EXCEPTION Example program ------> e_c17_p1.ada Examine the program named e_c17_p1.ada for our first example program with an exception handler. Ignore lines 18 and 19 for the moment and you will have a program that is not at all unusual, and should pose no problem for you to understand. The program does have a carefully introduced error however, because when we reach a value of 4 for Index in line 14, we will be attempting to divide by zero. Dividing by zero is not allowed in any programming language, because the answer is infinite and therefore undefined. The Ada runtime system will, by definition, cause the exception named Constraint_Error to be raised, which is the Ada way of saying that a divide by zero was attempted. This signals the system to do something about it. (Actually, there are many other ways to get the Constraint_Error exception raised but we will worry about them later.) The Ada system will search, in a very definite way, for any instructions we have given about this error, and if it finds none, will terminate operation of the program after issuing a message concerning the error. If we have given instructions about what to do with the error, it will exec

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