On Fri, Nov 13, 2009 at 02:15:27AM +0000, Harry Van Haaren wrote: It helps to clearly separate two things: 1. How a multithreaded program can be structured 2. A particular implementation of threads, e.g. Posix. (2) maybe suggests (1), but in fact the two are quite independent. For (1) there are several approaches: A1. Data is shared between threads, access to it is contolled by mutexes. A2. The CSP way: all data used by a thread strictly private to that thread. If another thread needs it, it is copied via a data channel. Threads can sync on data channels, i.e. they can wait for data to arrive. A3. As (A2) but data maybe transferred by just sending a pointer to it. The pointer message transfers ownner- ship - even if a thread could still access the data after having transmitted it, it will not do so until it receives the pointer again. The net result is the same as (A2), but it can be more efficient if large amounts of data have to be moved. A related issue is how to control the threads themselves in an application where threads could be added and removed dynamically: B1. Threads can be 'killed' by other threads. B2. Threads can not be terminated externally, but they are designed to terminate themselves when necessary or on request. (A1, B1) often go together, as do (A2, A3, B2). This is logical, as if thread data is private, only the thread itself can clean up before quitting, so no thread should ever be 'zapped'. The choice between these models is independent of the thread implementation you use. Mixing them in large applications is usually a recipe for trouble. (A1) is somewhat closer to actual low-level threads implementations, while (A2, A3) may require some thin layer on top of them, but such a layer can be made for whatever thread implementation. It also adds a degree of abstraction, and hence portability. Another feature of the CSP inspired models is that they can work on multiprocessor system where each processor has only private memory, and data channels between them are supported by hardware. Coming from a CSP bacground, I certainly do prefer (A2, A3) except maybe for very simple systems, but that could be a very personal preference. Ciao, -- FA Io lo dico sempre: l'Italia è troppo stretta e lunga.