2017-12-12 --
https://software.intel.com/en-us/articles/threading-models-for-high-performance-computing-pthreads-or-openmp
Talks about important differences b/w Pthreads and OpenMP thread apis and highlights the scenarios where each is more appropriate to use.
Important Points (directly copied from the article) --
The following definition of pragmas, taken from Microsoft’s documentation, is one of the clearest explanations: “The #pragma directives offer a way for each compiler to offer machine- and operating system-specific features while retaining overall compatibility with the C and C++ languages. Pragmas are machine- or operating system-specific by definition, and are usually different for every compiler. In C and C++, where they are most commonly used, pragmas have the form: #pragma token-string”.A key aspect of pragmas is that if a compiler does not recognize a given pragma, it must ignore it (according to the ANSI C and C++ standards). Hence, it is safe to place library-specific pragmas in code without worrying that the code will be broken if it compiled with a different toolset.
The OpenMP specification consists of APIs, a set of pragmas, and several settings for OpenMP-specific environment variables. As further revisions have been made to the standard, it has become clear that one of OpenMP’s most useful feature is its set of pragmas. By judicious use of these pragmas, a single-threaded program can be made multithreaded without recourse to APIs or environment variables.
OpenMP offers numerous other pragmas that identify code blocks to thread, scope variables to be shared across threads or local to individual threads, where to sync threads, how to schedule tasks or loop iterations to threads, and so forth. So, ultimately, it provides a medium-grained control over threading functionality. At this level of granularity, which is sufficient for many HPC applications, OpenMP delivers better than most other options on the promise of portability, optimal execution, and, especially, minimized disruption to the codebase.
OpenMP’s pragmas have another key advantage: by disabling support for OpenMP, the code can be compiled as a single-threaded application. Compiling the code this way can be tremendously advantageous when debugging a program. Without this option, developers will frequently find it difficult to tell whether complex code is working incorrectly because of a threading problem or because of a design error unrelated to threading.
Both APIs are portable, but Pthreads offers a much greater range of primitive functions that provide finer-grained control over threading operations. So, in applications in which threads have to be individually managed, Pthreads or the native threading API (such as Win32 on Windows) would be the more natural choice.
