ISO/IEC TR 19755:2003
(Main)Information technology — Programming languages, their environments and system software interfaces — Object finalization for programming language COBOL
Information technology — Programming languages, their environments and system software interfaces — Object finalization for programming language COBOL
ISO/IEC TR 19755:2003 specifies a feature for finalizing objects in COBOL. The specification is a Type 2 Technical Report so that implementations can be undertaken on an experimental basis. The experience gained is expected to result in an improved specification that can progress to standardization. The purpose of object finalization is to free resources that will not otherwise be freed by the normal garbage collection process. Examples include files that are open, temporary work files, database connections, TCP/IP socket interfaces and network connections.
Technologies de l'information — Langages de programmation, leurs environnements et interfaces logiciel système — Finalisation d'objet pour le langage de programmation COBOL
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TECHNICAL ISO/IEC
REPORT TR
19755
First edition
2003-12-01
Information technology — Programming
languages, their environments and
system software interfaces — Object
finalization for programming language
COBOL
Technologies de l'information — Langages de programmation, leurs
environnements et interfaces logiciel système — Finalisation d'objet
pour le langage de programmation COBOL
Reference number
ISO/IEC TR 19755:2003(E)
©
ISO/IEC 2003
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ISO/IEC TR 19755:2003(E)
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ISO/IEC TR 19755:2003(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Conformance to this Technical Report. 1
4 Terms and definitions. 1
5 Description techniques . 1
6 Changes to ISO/IEC 1989:2002 . 2
6.1 Changes to 7, Compiler directing facility . 2
6.2 Changes to 8, Language fundamentals . 2
6.3 Changes to 9, I-O, objects, and user-defined functions . 2
6.4 Changes to 10, Structured compilation group. 4
6.5 Changes to 11, Identification division . 4
6.6 Changes to 14, Procedure division . 5
6.7 Changes to 16, Standard classes. 7
Annex A (normative) Language element lists . 8
Annex B (informative) Unresolved technical issues. 9
Annex C (informative) Concepts . 10
Bibliography . 13
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ISO/IEC TR 19755:2003(E)
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are members of
ISO or IEC participate in the development of International Standards through technical committees
established by the respective organization to deal with particular fields of technical activity. ISO and IEC
technical committees collaborate in fields of mutual interest. Other international organizations, governmental
and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information
technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of the joint technical committee is to prepare International Standards. Draft International
Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as
an International Standard requires approval by at least 75 % of the national bodies casting a vote.
In exceptional circumstances, the joint technical committee may propose the publication of a Technical Report
of one of the following types:
— type 1, when the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts;
— type 2, when the subject is still under technical development or where for any other reason there is the
future but not immediate possibility of an agreement on an International Standard;
— type 3, when the joint technical committee has collected data of a different kind from that which is normally
published as an International Standard (“state of the art”, for example).
Technical Reports of types 1 and 2 are subject to review within three years of publication, to decide whether
they can be transformed into International Standards. Technical Reports of type 3 do not necessarily have to
be reviewed until the data they provide are considered to be no longer valid or useful.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.
ISO/IEC TR 19755:2003, which is a Technical Report of type 2, was prepared by Joint Technical Committee
ISO/IEC JTC 1, Information technology, Subcommittee SC 22, Programming languages, their environments
and system software interfaces, in collaboration with INCITS Technical Committee J4, Programming language
COBOL.
This document is being issued in the Technical Report (type 2) series of publications (according to the
Procedures for the technical work of ISO/IEC JTC 1) as a “prospective standard for provisional application” in
the field of object finalization in COBOL because there is an urgent need for guidance on how standards in
this field should be used to meet an identified need.
This document is not to be regarded as an “International Standard”. It is proposed for provisional application
so that information and experience of its use in practice may be gathered. Comments on the content of this
document should be sent to the ISO Central Secretariat.
A review of this Technical Report (type 2) will be carried out not later than three years after its publication with
the options of: extension for another three years; conversion into an International Standard; or withdrawal.
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ISO/IEC TR 19755:2003(E)
Introduction
This Technical Report specifies a feature for finalizing objects in COBOL. The feature is considered to be
immature and not ready for standardization. The decision was made to publish the specification in a Type 2
Technical Report so that implementations can be undertaken on an experimental basis. The experience
gained is expected to result in an improved specification that can progress to standardization.
In order to provide as much stability as possible to implementors and users, ISO/IEC JTC 1 Subcommittee 22
intends that the syntax and semantics be changed for purposes of standardization only as necessary to
address issues arising in implementation or use of the feature for finalizing objects.
The purpose of object finalization is to free resources that will not otherwise be freed by the normal garbage
collection process. Examples include files that are open, temporary work files, database connections, TCP/IP
socket interfaces, and network connections.
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TECHNICAL REPORT ISO/IEC TR 19755:2003(E)
Information technology — Programming languages, their
environments and system software interfaces — Object
finalization for programming language COBOL
1 Scope
This Technical Report specifies the syntax and semantics for object finalization in COBOL. The purpose of
this Technical Report is to promote a high degree of portability in implementations of object finalization, even
though some elements are subject to trial before completion of a final design suitable for standardization.
This specification builds on the syntax and semantics defined in ISO/IEC 1989:2002.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO/IEC 1989:2002, Information technology — Programming languages — COBOL
3 Conformance to this Technical Report
Conformance to this Technical Report requires conformance to ISO/IEC 1989:2002 as specified in Clause 3,
Conformance to this International Standard, and the normative specifications of this Technical Report.
4 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
4.1
auto-method
A special kind of method that is invoked only by the runtime system. An auto-method has the characteristics
of a method with certain specified exceptions.
4.2
finalizer
A kind of auto-method that is invoked by the runtime system before the resources of an instance object are
reclaimed by garbage collection.
5 Description techniques
Description techniques and language fundamentals are the same as those described in ISO/IEC 1989:2002.
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ISO/IEC TR 19755:2003(E)
6 Changes to ISO/IEC 1989:2002
These changes refer to Clause and rule numbers in ISO/IEC 1989:2002.
6.1 Changes to 7, Compiler directing facility
[a] Add the following sentence to the end of general rule 1) of 7.2.17.3, General rules:
Automatic propagation of exception conditions from a finalizer is always disabled.
6.2 Changes to 8, Language fundamentals
[a] Add a new reserved word to 8.9, Reserved words:
AUTO-METHOD
[b] Add a new context-sensitive word to 8.10, Context-sensitive words:
FINALIZER AUTO-METHOD paragraph
6.3 Changes to 9, I-O, objects, and user-defined functions
[a] Replace 9.3.14.1, Life cycle for factory objects, which says:
"A factory object is created before it is first referenced by a run unit.
A factory object is destroyed after it is last referenced by a run unit."
with
"A factory object is created before it is first referenced by a run unit. The state of a created factory object
is reachable.
A factory object is destroyed after it has been placed in unreachable state."
[b] Replace 9.3.14.2, Life cycle for instance objects, which says:
"An instance object is created as the result of the NEW method being invoked on a factory object.
An instance object is destroyed either when it is determined that the object cannot take part in the
continued execution of the run unit, or when the run unit terminates, whichever occurs first.
The timing of and algorithm for the mechanism that determines whether or not an instance object can
take part in the continued execution of the run unit is implementor defined.
NOTE The process of determining whether or not an instance object can take part in continued execution and
reclaiming resources unique to the object is generally referred to as garbage collection."
with
"An instance object is created as the result of the NEW method being invoked on a factory object. The
object returned is in reachable state. An object created in the range of finalization immediately transitions
to finalizable state.
An instance object is destroyed after it has been placed in unreachable state. The resources allocated for
the object may be reclaimed when it is destroyed.
The timing of and algorithm for the reclamation of resources are implementor defined.
NOTE The process of reclaiming resources unique to the object is generally referred to as garbage collection."
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ISO/IEC TR 19755:2003(E)
[c] Insert 9.3.14.3, Object finalization, and 9.3.14.4, State transitions of objects, after 9.3.14.2, Life cycle for
instance objects:
9.3.14.3 Object finalization
An auto-method, finalizer, of an object is invoked by the runtime system before the object is destroyed and the
resources of an instance object are reclaimed. The execution of finalizers on an object is called finalization of
the object. The range of execution of finalization includes all statements executed from the invocation of a
finalizer auto-method until its termination.
NOTE This may include the execution of statements in runtime elements outside the finalizer auto-method.
If more than one finalizer is defined in a class inheritance hierarchy of an object, each finalizer shall be
invoked after all finalizers that are defined in subclasses within that hierarchy have been invoked. There may
be more than one possible order of invocation. The order in which the finalizers are invoked is undefined,
except that no finalizer of a given class is invoked until finalizers of all its subclasses have completed. Each
finalizer associated with an object shall be invoked at most once for that object. During execution of a finalizer,
no other finalizers shall be invoked.
The finalization of an object is completed when control is returned to the runtime system after all associated
finalizers have been executed on the object. During finalization of an object, no other objects shall be under
finalization. The order of finalization among the objects is undefined.
During execution of the run unit, the timing of finalizer invocation is undefined.
NOTE Finalizer invocations may cause side effects within the COBOL run unit.
9.3.14.4 State transitions of objects
The object life cycle consists of four states: reachable, finalizable, finalized, and unreachable. The state
transitions occur in the following order:
1) Reachable
An object is reachable when it has been created in the reachable state and has not yet been determined
as finalizable. Reachable objects may be referenced during the finalization of finalizable objects.
2) Finalizable
An object is finalizable when it is determined that it can no longer participate in the continued execution of
the run unit outside of finalization. The timing of and algorithm for recognizing finalizable objects is
implementor-defined and may be affected by invoking the InvokeFinalizers method defined in the
standard class BASE. If no finalizer is associated with an object in this state, the state of the object
transitions to the finalized state. If one or more finalizers are associated with an object in this state, the
finalizers are invoked by the runtime system on the object. Finalizable objects may be referenced during
the finalization of other finalizable objects.
3) Finalized
All finalizers associated with the object have been invoked and completed. One or more finalizable
objects reference this object directly or indirectly through one or more finalized objects. Finalized objects
may be referenced during the finalization of finalizable objects.
4) Unreachable
The object has been finalized and no other finalizable object references this object directly or indirectly.
This state indicates that the object may be destroyed and its resources reclaimed by garbage collection.
The implementor shall define the time at which an object in unreachable state is destroyed.
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ISO/IEC TR 19755:2003(E)
NOTE An object reference to a finalizable object or a finalized object is not allowed to be implicitly or explicitly
assigned to a data item defined in a runtime element that is not part of finalization. Therefore, neither finalizable
objects nor finalized objects can become reachable again.
The state transitions that occur at the time a run unit is terminating are described in 14.5.10, Run unit
termination, and 14.5.11, Abnormal run unit termination.
6.4 Changes to 10, Structured compilation group
[a] Add a new auto-method format to 10.5.1, General format:
where auto-method-definition is:
[ IDENTIFICATION DIVISION. ]
AUTO-METHOD. FINALIZER.
[ options-paragraph ]
[ environment-division ]
[ data-division ]
[ procedure-division ]
END AUTO-METHOD.
[b] Add the new end marker END AUTO-METHOD to the end markers specified in 10.6.1, End markers,
General format.
6.5 Changes to 11, Identification division
[a] Add the new auto-method-paragraph to 11.1.1, General format.
[b] Add the following auto-method-paragraph specification to 11, Identification division:
11.6a AUTO-METHOD paragraph
The AUTO-METHOD paragraph indicates that this identification division is introducing an auto-method
definition.
11.6a.1 General format
Format 1 (finalizer):
AUTO-METHOD. FINALIZER.
11.6a.2 Syntax rules
1) The finalizer auto-method may be specified only in the object definition of a class definition.
2) The finalizer auto-method may be specified only once in a class definition.
11.6a.3 General rules
1) An auto-method has
...
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