Thread Attributes

Thread attributes provide a mechanism for fine-tuning the behavior of individual threads.
You may create and customize a thread attribute object to specify other values for the attributes. To specify customized thread attributes, you must follow these steps;
- Create a pthread_attr_t object. The easiest way is simply to declare an automatic variable of this type.
- Call pthread_attr_init, passing a pointer to this object. This initializes the attributes to their default values.
- Modify the attribute object to contain the desired attribute values.
- Pass a pointer to the attribute object when calling pthread_create.
- Call pthread_attr_destroy to release the attribute object. The pthread_attr_t variable itself is not deallocated; it may be reinitialized with pthread_attr_init.
A single thread attribute object may be used to start several threads. It is not necessary to keep the thread attribute object around after the threads have been created.
For most application programming tasks, only one thread attribute is typically of interest. This attribute is the thread's detach state.
A thread may be created as a joinable thread (the default) or as a detached thread.
- A joinable thread, like a process, is not automatically cleaned up when it terminates. (until another thread calls pthread_join to obtain its return value. Only then are its resources released.)
- A detached thread is cleaned up automatically when it terminates. Because a detached thread is immediately cleaned up, another thread may not synchronize on its completion by using pthread_join or obtain its return value.
The following code (see Fig. 5) creates a detached thread by setting the detach state thread attribute for the thread. http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/detached.cdetached.c

Figure 5: Skeleton Program That Creates a Detached Thread
$\begin{figure}\begin{center} \small \begin{verbatim}...$
Even if a thread is created in a joinable state, it may later be turned into a detached thread. To do this, call pthread_detach. Once a thread is detached, it cannot be made joinable again.

**Figure 5:** Skeleton Program That Creates a Detached Thread
$\begin{figure}\begin{center} \small \begin{verbatim}...$

Table 1 shows the thread attributes; the default values are marked with an asterisk.

**Table 1:** Thread Attributes
Attribute	Value	Meaning
detachstate	PTHREAD_CREATE_JOINABLE*	Joinable state
	PTHREAD_CREATE_DETACHED	Detached state
schedpolicy	SCHED_OTHER*	Normal, non-realtime
	SCHED_RR	Realtime, round-robin
	SCHED_FIFO	Realtime, first in first out
schedparam	policy specific
inheritsched	PTHREAD_EXPLICIT_SCHED*	Set by schedpolicy and schedparam
	PTHREAD_INHERIT_SCHED	Inherited from parent process
scope	PTHREAD_SCOPE_SYSTEM*	One system timeslice for each thread
	PTHREAD_SCOPE_PROCESS	Threads share same system timeslice (not supported under Linux)

2006-03-24