Skip to main content

C++ Multithreading - Basic thread creation

C++11 standard introduces integrated sublibrary for multithreading. It has been moved from Boost library. However because multithreading is very important topic in software development I decided to make multithreading tutorial as separate section of this blog.

I will not explain here theory about multithreading, but I will try to explain usage of multithreading based on thread library from C++11 standard. If theory explanation will be required for some aspects I will try to put links to separate articles explaining them.

Introduction theory about multithreading you can find on Wikipedia article here

This article will present basic threads creation and usage in C++. Code of example you can find here:
Output of the example is (it can be little other - depends how thread will be invoked by OS):
In point I we are creating new thread where print() function will be invoked. This thread will work in parallel to the main function (main application is second thread called main thread)

Point II shows printing values using for loop invoked from main thread.

Point III is invoking function join() which will wait until thread1 will finish. This is basic synchronization. Without that function there is possible that we will receive termination error if main thread finished and thread1 did not finished its job.

If we do not want to wait until thread1 will finish and do not want to receive termination error we could use detach() function (look point IV). Thanks to that function thread1 will be detached from our main application and will work in the background as deamon thread. We will be able to operate our next function without waiting for its finish if we do not need it.

Of course output of this example can be different on your machine. It depends how your OS schedule threads invoking. Threads are managed by OS so you can see different results if your threads are not synchronized properly. This is basic application so it does not contain sophisticated thread synchronization. I will explain how to synchronize threads in next articles.

This is first basic tutorial which presents how to create basic thread to run two separate function in parallel. In next multithreading articles I will show how to pass parameters for multithreading functions, return values, synchronize variables between threads and other thread-related topics.

Code of this example you can find on our GitHub account here: https://github.com/xmementoit/CppAdventureExamples/tree/master/multithreading/basicThreads

Source: http://www.javastudychannel.com/attachments/Resources/5002-23399-Multi-threaded-program.jpg

Labels:

Comments

Post a Comment

Popular posts from this blog

C++ Multithreading - Race conditions

In the previous C++ Multithreading article I presented you how to pass parameters between threads. Take a detail look on the output of that example once again: In the first line of that output you can notice that output text from two threads is mixed. You are probably wondering why it happens? It is because we are not protecting resources which are shared by two threads (in this example cout stream is shared in both threads) which causes multithreading's phenomenon called race condition . Because threads switching and accessing to shared resources are managed by operating system we do not know when std::cout stream will be accessed by main thread and when it will be accessed by second thread. Therefore in the previous article I mentioned that output of the example can be little different on your computer than my output example. What's more it is possible that this output will be different for few consecutive invoking of the example on the same machine. It is beca...
Post a Comment
Read more

Advanced C++ - Template Functions

Template function are special types of C++ function which can be used with different types (generic types). Thanks to that we can create one body of function which can be used for many different types. When we are creating template function compiler does not define any function for use at that time. Generation of funciton basing on templates are done during compilation process basing of differnt usage of template class. For better understanding take a look on following example: Output of this example is: In point I, we are defining template function which should return sum of two parameters. Without templates we need to define such function separately for each type which we should use it with (ex. separate function for int type, separate for double , separate for any other type). Thanks to template we can generate body of that function only once (as in point I) and use it to any type which is able to use body of that function. In our example we can use this template for an...
Post a Comment
Read more

Advanced C++ - Stack unwinding

Stack unwinding is normally a concept of removing function entries from call stack (also known as Execution stack, Control stack, Function stack or Run-time stack). Call Stack is a stack data structure that stores active functions' addresses and helps in supporting function call/return mechanism. Every time when a function is called, an entry is made into Call stack which contains the return address of the calling function where the control needs to return after the execution of called function. This entry is called by various names like stack frame , activation frame or activation record. With respect to exception handling , stack Unwinding is a process of linearly searching function call stack to reach exception handler. When an exception occurs, if it is not handled in current function where it is thrown, the function Call Stack is unwound until the control reaches try block and then passes to catch block at the end of try block to handle exception. Also, in this proc...
Post a Comment
Read more