Attributes provide a way to specify behavior that is different from the default thread creation behavior. When a thread is created with pthread_create(3C) or when a synchronization variable is initialized, an attribute object can be specified. The defaults are usually sufficient.
An attribute object is opaque, and cannot be directly modified by assignments. A set of functions is provided to initialize, configure, and destroy each object type.
Once an attribute is initialized and configured, the attribute has process-wide scope. The suggested method for using attributes is to configure all required state specifications at one time in the early stages of program execution. The appropriate attribute object can then be referred to as needed.
The use of attribute objects provides two primary advantages.
Using attribute objects adds to code portability.
Even though supported attributes might vary between implementations, you need not modify function calls that create thread entities. These function calls do not require modification because the attribute object is hidden from the interface.
If the target port supports attributes that are not found in the current port, provision must be made to manage the new attributes. Management of these attributes is an easy porting task because attribute objects need only be initialized once in a well-defined location.
State specification in an application is simplified.
As an example, consider that several sets of threads might exist within a process. Each set of threads provides a separate service. Each set has its own state requirements.
At some point in the early stages of the application, a thread attribute object can be initialized for each set. All future thread creations will then refer to the attribute object that is initialized for that type of thread. The initialization phase is simple and localized. Any future modifications can be made quickly and reliably.
Attribute objects require attention at process exit time. When the object is initialized, memory is allocated for the object. This memory must be returned to the system. The pthreads standard provides function calls to destroy attribute objects.
Pthreads functions can be used to manipulate thread attribute objects. The functions are described in the following sections.