Threads in Linux
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Transcript of Threads in Linux
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Threads
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Multiple strands of execution ina single program are calledthreads.
A more precise defnition is thata thread is a sequence of controlwithin a process.
threads, which allow a singleprocess to multitask.
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When a process executes a forkcall, a new copy of the process is
created with its own variables andits own P!.
When we create a new threadina process, in contrast, the newthread of execution gets its ownstack "and hence local variables#but shares global variables, $ledescriptors, signal handlers withthe rocess that created it.
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Advantages
% &ometimes it is very useful to make a
program appear to do two things atonce. The classic example is to performa real'time word count on a documentwhile still editing the text. (ne thread
can manage the user)s input andperform editing.
% The performance of an applicationthat mixes input, calculation, andoutput may be improvedby running these as three separate
threads. While the input or output
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Advantages
% better utili*ation of thehardware resources available.
% n general, switchingbetween threads requires the
operating system to do muchless work than switchingbetween processes.
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Drawbacks
% Writing multithreadedprograms requires very carefuldesign.
% !ebugging a multithreadedprogram is much, much harderthan debugging a single'threaded one
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pthread_create creates anew thread
+include pthread.h-
int pthreadcreate"pthreadt/thread, pthreadattrt /attr,
void/"/startroutine#"void /#, void/arg#0
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#include void pthread_exit(void*retval!
pthread1oin is the threadequivalent of wait that processesuse to collect child processes.
This function is declared asfollows2#include
int pthread_"oin(pthread_t th**
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+include stdio.h-+include unistd.h-+include stdlib.h-
+include string.h-+include pthread.h-void /threadfunction"void /arg#0char message34 5 67ello World80int main"# 9int res0pthreadt athread0void /threadresult0res 5 pthreadcreate":athread, ;5 ?# 9perror"6Thread creation failed8#0exit"@ATBC=
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printf"6Waiting for thread to $nish...Fn8#0res 5 pthread1oin"athread, :threadresult#0if "res >5 ?# 9
perror"6Thread 1oin failed8#0exit"@ATBC=
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cc -D_REENTRANT thread1.c othread1 lpthread
K .$thread%Waiting for thread to $nish...
threadfunction is running. Crgumentwas 7ello WorldThread 1oined, it returned Thank youfor the HP< time
Message is now Jye>
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&imultaneous @xecution of Two Threadsint runnow 5 L0int printcountL 5 ?0while"printcountL N?# 9
if "runnow 55 L# 9printf"6L8#0runnow 5 N0Eelse 9
sleep"L#0EEint printcountN 5 ?0while"printcountN N?# 9if "runnow 55 N# 9
printf"6N8#0runnow 5 L0Eelse 9sleep"L#0EE
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K cc &D_')'A) thread+.c &othread+ &lpthread
K .$thread+
LNLNLNLNLNLNLNLNLNLNWaiting for thread to $nish...
Thread 1oined
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,-nchroniation
Synchronization with Semaphores
Synchronization with Mutexes
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Semaphores
C semaphore is nothing but a term
used in
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Mutexes
Mutexes are typically used toserialise access to a section of re'entrant code that cannot be executedconcurrently by more than onethread.
C mutex ob1ect only allows one
thread into a controlled section,forcing other threads which attemptto gain access to that section to wait
until the $rst thread has exited from8
