Multithreading

The embedded libraries (libebd.u.a and libebd.s.a) and the libc.a and libstdc++.a libraries have been made thread-safe to support multithreaded actors. Multithreading is managed by the library in the following way:

• Protecting shared variables with mutexes.

• Using the Private Data library to maintain private variables per thread (for errno management, see the next section).

Defining errno as a single global variable for an actor is not suitable for multithreaded actors. Situations can arise where a thread, when examining errno on return from a failed system call, concludes that the call failed for the wrong reason (because the global errno was changed by another system call in another thread in the meantime). Some programs also test errno rather than system call return values to detect errors.

To prevent global errno changes by another system call, the header file errno.h (which is exported by the POSIX environment) should be included in any source file using errno. This will result in a separate value of errno for each thread.