Ada Programming/Pragmas/Shared

Pragmas Shared __TOC__ pragma Shared (local_name); Summary Shared is an Ada 83 representation pragma equivalent to Atomic. pragma Shared (was Ada is almost ....) Robert Dewar 1996-02-17 comp.lang.ada http://groups.google.es/group/comp.lang.ada/msg/eeee3a7515837ea2 2008-05-28 pragma Atomic is QUITE different from pragma Volatile. pragma Atomic in Ada is essentially identical to pragma Shared in Ada 83. pragma Volatile in Ada is essentially identical to volatile in C, and is a feature that is not available in Ada 83. However, it can only be applied to variables, whereas Atomic can also be used with types. It was removed from the language in Ada 95 for several reasons: it was not properly defined Laurent Guerby Ada 95 Rationale January 1995 C 5 Shared Variable Control 3 Intermetrics 2008-05-28 The pragma Shared was quite weak. The semantics were only defined in terms of tasks, and not very clearly. This made it inadequate for communication with non-Ada software or hardware devices. Moreover, it could be applied only to a limited set of objects. For example, it could not be applied to a component of an array. it couldn't be applied to arrays the name Shared was confusing Annotated Ada 95 Reference Manual C.6 Shared Variable Control http://www.adaic.com/standards/95aarm/html/AA-C-6.html#I6739 2008-05-28 Pragma Atomic replaces Ada 83's pragma Shared. The name Shared was confusing, because the pragma was not used to mark variables as shared. In Ada 95 pragma Shared was replaced by pragma Atomic, Volatile, Atomic_Components, and Volatile_Components. Portability Shared is a standard pragma of Ada 83, so it must be implemented by all Ada 83 compilers. It is obsolescent in successive versions of the language, but it is equivalent to pragma Atomic and thus it is usually implemented by Ada 95 compilers for compatibility. GNAT Pro Reference Manual Implementation Defined Pragmas http://www.adacore.com/wp-content/files/auto_update/gnat-unw-docs/html/gnat_rm_2.html#SEC91 AdaCore 2008-05-28 This pragma is provided for compatibility with Ada 83. The syntax and semantics are identical to pragma Atomic. Example type Device_Status : Status_Register; Shared (Device_Status); Incorrect usage It is usually unsafe to use shared variables for tasking. Ada 83 Quality and Style Software Productivity Consortium, Inc 7 4 7 Shared Variables and Pragma Shared 07 04 2008-05-28 Do not use shared variables as a task synchronization device. Use pragma Shared only when you are forced to by run time system deficiencies. See also Wikibook Ada Programming Ada Programming/Ada 83 Ada Programming/Pragmas Ada Programming/Pragmas/Atomic Ada Programming/Pragmas/Volatile Ada Programming/Pragmas/Atomic Components Ada Programming/Pragmas/Volatile Components Ada 83 Reference Manual 9 11 Shared Variables B Predefined Language Pragmas Ada 95 Rationale C 5 Shared Variable Control 3 Ada 83 Rationale 13 2 3 Visibility Rules 13 02 Ada 83 Quality and Style Guide 6 2 4 Shared Variables 06 02 7 4 7 Shared Variables and Pragma Shared 07 04 References Shared Shared