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. 5.5) 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 5.5: Skeleton Program That Creates a Detached Thread

  
• 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.
• Table 5.1 shows the thread attributes; the default values are marked with an asterisk.

  
  

  Table 5.1: 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)