Posix Threads

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Posix Threads

• Shared address systems
• Will become more of an issue as higher core
  processors become more available.
• POSIX Portable Operating System Interface

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Simple Example

• include ltpthread.hgt
• int err
• void main()
• pthread_t tidMAX
• for (i0 iltt i)
• errpthread_create(tidi,NULL,
  count3s,i)
• for (i0iltti)
• errpthread_join(tidi, (void )
  statusi)

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Code Spec 6.1 pthread_create(). The POSIX
Threads thread creation function.
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Code Spec 6.2 pthread_join(). The POSIX Threads
rendezvous function.
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Code Spec 6.3 pthread_self(). The POSIX Threads
function to fetch a threads ID.
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Code Spec 6.4 pthread_equal(). The POSIX Threads
function to compare two thread IDs for equality.
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Code Spec 6.5 pthread_exit(). The POSIX Threads
thread termination function.
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Pthread Attributes

• Uses type pthread_attr_t
• Detached or Joinable
• Detached cannot be joined (less overhead)
• For us, rarely needed
• Bound or Unbound
• Bound threads are scheduled by OS (what we use
  mostly)
• Unbound scheduled by threads library

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Code Spec 6.6 pthread attributes. An example of
how thread attributes are set in the POSIX
Threads interface.
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Be Careful pass addresses, not values

• void main()
• pthread_t tid int status
• pthread_create(tid, NULL, start, NULL)
• pthread_join(tid, (void ) status)
• void start()
• int errorcode
• errorcodesomething
• pthread_exit(errorcode) ? problem here

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Code Spec 6.7 The POSIX Threads routines for
acquiring and releasing mutexes.
pthread_mutex_t lockPTHREAD_MUTEX_INITIALIZER
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Code Spec 6.8 The POSIX Threads routines for
dynamically creating and destroying mutexes.
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Code Spec 6.9 An example of how dynamically
allocated mutexes are used in the POSIX Threads
interface.
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Figure 6.1
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Code Spec 6.10 pthread_cond_wait(). The POSIX
Thread routines for waiting on condition
variables.
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Code Spec 6.11 pthread_cond_signal(). The POSIX
Threads routines for signaling a condition
variable.
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Figure 6.3 Bounded buffer example using
condition variables nonempty and nonfull.
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Figure 6.4 Example of why a signaling thread
needs to be protected by a mutex.
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Code Spec 6.12 The POSIX Threads routines for
dynamically creating and destroying condition
variables.
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Figure 6.6 Example of thread-specific data in
POSIX Threads. Thread-specific data are accessed
by keys, which map to different memory locations
in different threads.
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Code Spec 6.13 Example of how thread-specific
data is used. Once initialized with this code,
any procedure can access the value of my_index.
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Code Spec 6.14 pthread_key_create(). POSIX
Thread routine for creating a key for
thread-specific data.
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Code Spec 6.15 pthread_key_delete(). POSIX
Thread routine for deleting a key.
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Code Spec 6.16 pthread_setspecific(). POSIX
Thread routine for setting the value of
thread-specific data.
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Code Spec 6.17 pthread_getspecific(). POSIX
Thread routine for getting the value of some
thread-specific data.