Thread Create Attributes

The previous chapter covered the basics of threads creation using default attributes. This chapter discusses setting attributes at thread creation time.

Note that only pthreads uses attributes and cancellation, so the API covered in this chapter is for POSIX threads only. Otherwise, the functionality for Solaris threads and pthreads is largely the same. (See Chapter 9, Programming With Solaris Threads, for more information about similarities and differences.)

• Initialize Attributes

• Destroy Attributes

• Set Detach State

• Get Detach State

• Set Stack Guard Size

• Get Stack Guard Size

• Set Scope

• Get Scope

• Set Thread Concurrency Level

• Get Thread Concurrency Level

• Set Scheduling Policy

• Get Scheduling Policy

• Set Inherited Scheduling Policy

• Get Inherited Scheduling Policy

• Set Scheduling Parameters

• Get Scheduling Parameters

• Set Stack Size

• Get Stack Size

• Set Stack Address

• Get Stack Address

Attributes

Attributes are a way to specify behavior that is different from the default. When a thread is created with pthread_create(3THR) 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, it 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.

Using attribute objects has two primary advantages.

• First, it adds to code portability.

  Even though supported attributes might vary between implementations, you need not modify function calls that create thread entities 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. This is an easy porting task though, because attribute objects need only be initialized once in a well-defined location.

• Second, state specification in an application is simplified.

  As an example, consider that several sets of threads might exist within a process, each providing a separate service, and each with 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 initialized for that type of thread. The initialization phase is simple and localized, and 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 it. This memory must be returned to the system. The pthreads standard provides function calls to destroy attribute objects.

Initialize Attributes

pthread_attr_init(3THR)

Use pthread_attr_init(3THR) to initialize object attributes to their default values. The storage is allocated by the thread system during execution.

Prototype:

int pthread_attr_init(pthread_attr_t *tattr);

#include <pthread.h>

pthread_attr_t tattr;
int ret;

/* initialize an attribute to the default value */
ret = pthread_attr_init(&tattr);

Table 3-1 shows the default values for attributes (tattr) .

Table 3-1 Default Attribute Values for tattr