7.6.1 Completion and Finalization
This subclause defines completion and leaving of the execution of constructs and entities. A master is the execution of a construct that includes finalization of local objects after it is complete (and after waiting for any local tasks -- see 9.3), but before leaving. Other constructs and entities are left immediately upon completion.
The execution of a construct or entity is complete when the end of that execution has been reached, or when a transfer of control (see 5.1) causes it to be abandoned. Completion due to reaching the end of execution, or due to the transfer of control of an exit_, return_, goto_, or requeue_statement or of the selection of a terminate_alternative is normal completion. Completion is abnormal otherwise -- when control is transferred out of a construct due to abort or the raising of an exception.
After execution of a construct or entity is complete, it is left, meaning that execution continues with the next action, as defined for the execution that is taking place. Leaving an execution happens immediately after its completion, except in the case of a master: the execution of a task_body, a block_statement, a subprogram_body, an entry_body, or an accept_statement. A master is finalized after it is complete, and before it is left.
For the finalization of a master, dependent tasks are first awaited, as explained in 9.3. Then each object whose accessibility level is the same as that of the master is finalized if the object was successfully initialized and still exists. These actions are performed whether the master is left by reaching the last statement or via a transfer of control. When a transfer of control causes completion of an execution, each included master is finalized in order, from innermost outward.
For the finalization of an object:
- If the object is of an elementary type, finalization has no effect;
- If the object is of a controlled type, the Finalize procedure is called;
- If the object is of a protected type, the actions defined in 9.4 are performed;
- If the object is of a composite type, then after performing the above actions, if any, every component of the object is finalized in an arbitrary order, except as follows: if the object has a component with an access discriminant constrained by a per-object expression, this component is finalized before any components that do not have such discriminants; for an object with several components with such a discriminant, they are finalized in the reverse of the order of their component_declarations.
Immediately before an instance of Unchecked_Deallocation reclaims the storage of an object, the object is finalized. If an instance of Unchecked_Deallocation is never applied to an object created by an allocator, the object will still exist when the corresponding master completes, and it will be finalized then.
The order in which the finalization of a master performs finalization of objects is as follows: Objects created by declarations in the master are finalized in the reverse order of their creation. For objects that were created by allocators for an access type whose ultimate ancestor is declared in the master, this rule is applied as though each such object that still exists had been created in an arbitrary order at the first freezing point (see 13.14) of the ultimate ancestor type.
The target of an assignment statement is finalized before copying in the new value, as explained in 7.6.
If the object_name in an object_renaming_declaration, or the actual parameter for a generic formal in out parameter in a generic_instantiation, denotes any part of an anonymous object created by a function call, the anonymous object is not finalized until after it is no longer accessible via any name. Otherwise, an anonymous object created by a function call or by an aggregate is finalized no later than the end of the innermost enclosing declarative_item or statement; if that is a compound_statement, the object is finalized before starting the execution of any statement within the compound_statement.
Bounded (Run-Time) Errors
It is a bounded error for a call on Finalize or Adjust that occurs as part of object finalization or assignment to propagate an exception. The possible consequences depend on what action invoked the Finalize or Adjust operation:
- For a Finalize invoked as part of an assignment_statement, Program_Error is raised at that point.
- For an Adjust invoked as part of the initialization of a controlled object, other adjustments due to be performed might or might not be performed, and then Program_Error is raised. During its propagation, finalization might or might not be applied to objects whose Adjust failed. For an Adjust invoked as part of an assignment statement, any other adjustments due to be performed are performed, and then Program_Error is raised.
- For a Finalize invoked as part of a call on an instance of Unchecked_Deallocation, any other finalizations due to be performed are performed, and then Program_Error is raised.
- For a Finalize invoked as part of the finalization of the anonymous object created by a function call or aggregate, any other finalizations due to be performed are performed, and then Program_Error is raised.
- For a Finalize invoked due to reaching the end of the execution of a master, any other finalizations associated with the master are performed, and Program_Error is raised immediately after leaving the master.
- For a Finalize invoked by the transfer of control of an exit_, return_, goto_, or requeue_statement, Program_Error is raised no earlier than after the finalization of the master being finalized when the exception occurred, and no later than the point where normal execution would have continued. Any other finalizations due to be performed up to that point are performed before raising Program_Error.
- For a Finalize invoked by a transfer of control that is due to raising an exception, any other finalizations due to be performed for the same master are performed; Program_Error is raised immediately after leaving the master.
- For a Finalize invoked by a transfer of control due to an abort or selection of a terminate alternative, the exception is ignored; any other finalizations due to be performed are performed.
18 The rules of Section 10 imply that immediately prior to partition termination, Finalize operations are applied to library-level controlled objects (including those created by allocators of library-level access types, except those already finalized). This occurs after waiting for library-level tasks to terminate.
19 A constant is only constant between its initialization and finalization. Both initialization and finalization are allowed to change the value of a constant.
20 Abort is deferred during certain operations related to controlled types, as explained in 9.8. Those rules prevent an abort from causing a controlled object to be left in an ill-defined state.
21 The Finalize procedure is called upon finalization of a controlled object, even if Finalize was called earlier, either explicitly or as part of an assignment; hence, if a controlled type is visibly controlled (implying that its Finalize primitive is directly callable), or is nonlimited (implying that assignment is allowed), its Finalize procedure should be designed to have no ill effect if it is applied a second time to the same object.
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Copyright © 2000 The MITRE Corporation, Inc. Ada Reference Manual