Professor: Shu-Ching Chen
TA: Hsin-Yu Ha
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An independent stream of instructions that
can be scheduled to run
A path of execution
Multi-Thread
Single-Thread
Sequentially execute
CPU
int a, b;
int c;
a = 1;
b = a + 2;
c = 3;
int a, b;
int c;
a = 1;
b = a + 2;
c = 5;
CPU
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Program
 An execution file stored in the harddrive
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Process
 An execution file stored in the Memory
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Thread
 An execution path of part of the process
Program
HDD
Process
Memory
Thread
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Parallel execution
Shared resources
Easier to create and destroy than processes
(100X)
Easy porting to multiple CPUs
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Standardized C language threads programming
interface for UNIX systems
Four major groups
 Thread management: Routines that work directly on
threads - creating, detaching, joining, etc.
 Mutex: Routines that deal with synchronization. Mutex
functions provide for creating, destroying, locking and
unlocking mutexes.
 Condition variable: Routines that address
communications between threads that share a mutex.
 Synchronization: Routines that manage read/write
locks and barriers.
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pthread_create()
Return 0 if OK, nonzero on error
 Four Arguments
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Thread : A thread identifier
Attr : A pointer to a thread attribute object
Start_routine : A pointer to the function the thread executes
Arg : The argument to the function
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Single variable
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Several variables
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pthread_exit()Return 0 if OK, nonzero on error
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Four ways of terminating a thread
 The thread returns from its starting routine
 The thread makes a call to the pthread_exit subroutine
 The thread is canceled by another thread
 The entire process is terminated
 If main() finishes first, without calling pthread_exit
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Example of pthread_exit()
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pthread_join()Return 0 if OK, nonzero on error
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Wait from other threads to terminate by
calling it
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pthread_self()
 It returns the unique, system assigned thread ID of the calling thread
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pthread_detach()
Return 0 if OK, nonzero on error
 It can be used to explicitly detach a thread
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Join
Mutexes
Condition variables
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Mutexes are used
 to prevent data inconsistencies due to operations by
multiple threads upon the same memory area performed
at the same time
 to prevent race conditions where an order of operation
upon the memory is expected
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Condition variables are used
 to allow threads to synchronize based upon the actual
value of data without continually polling to check whether
the condition if met
 in conjunction with a mutex lock
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POSIX Threads Programming
 https://computing.llnl.gov/tutorials/pthreads/
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Pthreads primer
 http://pages.cs.wisc.edu/~travitch/pthreads_prim
er.html
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POSIX thread (pthread) Tutorial
 http://www.yolinux.com/TUTORIALS/LinuxTutori
alPosixThreads.html