HP WBEM Services Software Developer's Kit for HP-UX Provider and Client Developer's Guide A.01

Provider Implementation

Provider Design Considerations

Chapter 4 67

Use of Empty String Key Values

While the full set of keys is necessary to uniquely identify an instance

within a namespace, it is useful to allow clients to specify empty strings

for key values when there is no ambiguity. For example, when a client

submits a getInstance() operation to a CIM Server, it is clear that the

value of the SystemName key will normally be the same as the system to

which the client has connected. This is especially useful when managing

a multi-homed system (a system that may have more than one IP

address or DNS name), since the client need not guess the value of

SystemName when there can be several different hostnames for the same

system. Unless the provider has a reason to require a value for

SystemName, it should accept an empty string for this key without

returning an error. As a general rule, providers should accept empty

strings for any keys that they do not actually require to identify an

instance from among those they manage. However, the provider should

always supply values for all keys when returning data to the client.

Multi-Threading for Concurrent Requests

The CIM Server can process several client requests in different threads

concurrently in the same provider. Therefore, provider code must be

100% thread-reentrant and must avoid/prevent concurrent access of

any shared resources. If shared (global) resources are used, access must

be serialized by the use of a suitable semaphore (or mutex) to protect the

shared resource against modiﬁcation that could lead to erroneous

behavior. This is particularly important in provider interface methods

that alter platform behavior, such as modifyInstance(),

createInstance(), and deleteInstance(), but applies to any code

that manipulates a globally accessible resource or may have a side effect.

Information on developing thread-safe applications can be found online

in documentation for the aCC C++ compiler at

http://www.docs.hp.com.

Global Symbols

While all providers implement functions of the same names (for example,

getInstance()), there is no duplication of symbol names for symbols

deﬁned within a C++ provider classes. The C++ compiler generates