#Pthread c how to#
#Pthread c code#

Note: The whole explanation in this article is done on Posix threads. It depends on the OS scheduling algorithm. Well one point to be noted here is that the order of execution of threads is not always fixed. threadsР”Р„s seen in the output, first thread is created and it starts processing, then the second thread is created and then it starts processing.

#Pthread c code#

Now, when the above code is run, following was the output : $. Also, Inside the same function РІР‚ВdoSomeThing()РІР‚в„ў a for loop is run so as to simulate some time consuming work.Inside the function РІР‚ВdoSomeThing()РІР‚в„ў, the thread uses pthread_self() and pthread_equal() functions to identify whether the executing thread is the first one or the second one as created.

The starting function for both the threads is kept same.

It uses the pthread_create() function to create two threads.

Printf(' Thread created successfully ') Printf(' can't create thread :', strerror(err)) #includeР”В®rr = pthread_create(&(tid), NULL, &doSomeThing, NULL) Now, why a void type was chosen? This was because if a function accepts more than one argument then this pointer could be a pointer to a structure that may contain these arguments.Р”Р‡ollowing is the example code where we tried to use all the three functions discussed above.

As the function (whose address is passed in the third argument above) may accept some arguments also so we can pass these arguments in form of a pointer to a void type.

This is something to keep in mind that each thread starts with a function and that functions address is passed here as the third argument so that the kernel knows which function to start the thread from.

The third argument is a function pointer.

The second argument may contain certain attributes which we want the new thread to contain.

Once the function is called successfully, the variable whose address is passed as first argument will hold the thread ID of the newly created thread.

The first argument is a pthread_t type address.

The above function requires four arguments, lets first discuss a bit on them : Int pthread_create(pthread_t *restrict tidp, const pthread_attr_t *restrict attr, void *(*start_rtn)(void), void *restrict arg) A process can create extra threads using the following function : #include So we can say that every process has at least one thread of control. Normally when a program starts up and becomes a process, it starts with a default thread. Now individual worker threads parse the linked list and extract the job assigned to them. Now whenever a thread tries to fetch its data from linked list, it first gets its own ID by calling РІР‚Вpthread_self()РІР‚в„ў and then it calls the РІР‚Вpthread_equal()РІР‚в„ў on every node to see if the node contains data for it or not.Р”Р„n example of the generic case discussed above would be the one in which a master thread gets the jobs to be processed and then it pushes them into a link list. Every node in the list contains a thread ID and the corresponding data. Suppose there is a case where a link list contains data for different threads. Now, one would ask about the case where the above two function would be required. So we see that the function РІР‚Вpthread_self()РІР‚в„ў is used by a thread for printing its own thread ID. For this case the following function provides the desired service. So as you can see that the above function takes two thread IDs and returns nonzero value if both the thread IDs are equal or else it returns zero.Р”Р„nother case may arise when a thread would want to know its own thread ID. Int pthread_equal(pthread_t tid1, pthread_t tid2) As we already discussed that in most of the cases this type is a structure, so there has to be a function that can compare two thread IDs. Thread ID is represented by the type РІР‚Вpthread_tРІР‚в„ў. The above points give an idea about the difference between a process ID and thread ID.

A process ID can be printed very easily while a thread ID is not easy to print.

A process ID is an integer value but the thread ID is not necessarily an integer value.

A process ID is unique across the system where as a thread ID is unique only in context of a single process.

But interestingly, the similarity between the two ends here. Just as a process is identified through a process ID, a thread is identified by a thread ID. Linux Threads Series: part 1, part 2 (this article), part 3.

#Pthread c how to#

We will also present a working C program example that will explain how to do basic threaded programming. In this article we will focus on how a thread is created and identified. In the part I of the Linux Threads series, we discussed various aspects related to threads in Linux.