Are there deprecated practices for multithread and multiprocessor programming that I should no longer use?
- by DeveloperDon
In the early days of FORTRAN and BASIC, essentially all programs were written with GOTO statements. The result was spaghetti code and the solution was structured programming.
Similarly, pointers can have difficult to control characteristics in our programs. C++ started with plenty of pointers, but use of references are recommended. Libraries like STL can reduce some of our dependency. There are also idioms to create smart pointers that have better characteristics, and some version of C++ permit references and managed code.
Programming practices like inheritance and polymorphism use a lot of pointers behind the scenes (just as for, while, do structured programming generates code filled with branch instructions). Languages like Java eliminate pointers and use garbage collection to manage dynamically allocated data instead of depending on programmers to match all their new and delete statements.
In my reading, I have seen examples of multi-process and multi-thread programming that don't seem to use semaphores. Do they use the same thing with different names or do they have new ways of structuring protection of resources from concurrent use?
For example, a specific example of a system for multithread programming with multicore processors is OpenMP. It represents a critical region as follows, without the use of semaphores, which seem not to be included in the environment.
th_id = omp_get_thread_num();
#pragma omp critical
{
cout << "Hello World from thread " << th_id << '\n';
}
This example is an excerpt from: http://en.wikipedia.org/wiki/OpenMP
Alternatively, similar protection of threads from each other using semaphores with functions wait() and signal() might look like this:
wait(sem);
th_id = get_thread_num();
cout << "Hello World from thread " << th_id << '\n';
signal(sem);
In this example, things are pretty simple, and just a simple review is enough to show the wait() and signal() calls are matched and even with a lot of concurrency, thread safety is provided. But other algorithms are more complicated and use multiple semaphores (both binary and counting) spread across multiple functions with complex conditions that can be called by many threads. The consequences of creating deadlock or failing to make things thread safe can be hard to manage.
Do these systems like OpenMP eliminate the problems with semaphores?
Do they move the problem somewhere else?
How do I transform my favorite semaphore using algorithm to not use semaphores anymore?
