E.1 Partitions
The partitions of a distributed program are classified
as either active or passive.
Post-Compilation Rules
An
active
partition is a partition as defined in
10.2.
A
passive partition is a partition that has no thread of control
of its own, whose library units are all preelaborated, and whose data
and subprograms are accessible to one or more active partitions.
A passive partition shall include only
library_items
that either are declared pure or are shared passive (see
10.2.1
and
E.2.1).
An active partition shall be configured on a processing
node. A passive partition shall be configured either on a storage node
or on a processing node.
The configuration of the partitions of a program
onto a distributed system shall be consistent with the possibility for
data references or calls between the partitions implied by their semantic
dependences.
Any reference to data or call of a subprogram
across partitions is called a
remote access.
Dynamic Semantics
A
library_item
is elaborated as part of the elaboration of each partition that includes
it. If a normal library unit (see
E.2) has
state, then a separate copy of the state exists in each active partition
that elaborates it. The state evolves independently in each such partition.
An
active partition
terminates when its environment task terminates.
A partition becomes
inaccessible if it terminates or if it is
aborted. An active partition is aborted when its environment task
is aborted. In addition, if a partition fails during its elaboration,
it becomes inaccessible to other partitions. Other implementation-defined
events can also result in a partition becoming inaccessible.
For a
prefix
D that denotes a library-level declaration, excepting a declaration of
or within a declared-pure library unit, the following attribute is defined:
D'Partition_Id
Denotes a value of the type
universal_integer
that identifies the partition in which D was elaborated. If D denotes
the declaration of a remote call interface library unit (see
E.2.3)
the given partition is the one where the body of D was elaborated.
Bounded (Run-Time) Errors
It is a bounded error for there
to be cyclic elaboration dependences between the active partitions of
a single distributed program.
The possible effects,
in each of the partitions involved, are deadlock during elaboration,
or the raising of Communication_Error or Program_Error.
Implementation Permissions
An implementation may allow multiple active or passive
partitions to be configured on a single processing node, and multiple
passive partitions to be configured on a single storage node. In these
cases, the scheduling policies, treatment of priorities, and management
of shared resources between these partitions are implementation defined.
An implementation may allow separate copies of an
active partition to be configured on different processing nodes, and
to provide appropriate interactions between the copies to present a consistent
state of the partition to other active partitions.
In an implementation, the partitions of a distributed
program need not be loaded and elaborated all at the same time; they
may be loaded and elaborated one at a time over an extended period of
time. An implementation may provide facilities to abort and reload a
partition during the execution of a distributed program.
An implementation may allow the state of some of
the partitions of a distributed program to persist while other partitions
of the program terminate and are later reinvoked.
3 Library units are grouped into partitions
after compile time, but before run time. At compile time, only the relevant
library unit properties are identified using categorization pragmas.
4 The value returned by the Partition_Id
attribute can be used as a parameter to implementation-provided subprograms
in order to query information about the partition.
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