Multithreaded concept

Multithreaded concept for our multi-library SW setting:

• Some of our libraries need their own TLS
• xthread should provide the basic support for C++:
  • Common TLS Structure that accommodates places for all of our libs: void* lib_tls[MAXLIBID] = 0,0,0...0;
  • Common TLS macros for getting at it
  • new_thread, which should take Init and Done as well as run function pointers for setting up TLS for all the needed Libs: in their dependency order!
  • LIBIDs as #define's

Small steps (plan):

• Start with SW
• Make sure findexec is used readonly and thus is thread-safe
• Cristian makes his variant of omalloc - thread-safe
• since factory is not thread-safe and uses NTL - guard all the calls into factory with a lock: TODO for a HiWi, this should better be ifdef'ed depending on HAVE_THREADS(!?)
• the rest of our libs: libpolys, kernel, Singular (numeric?) should make use of the above "Multi-library concept":
  1. identify all the global variables
  2. Document all readonly global variables (with a single global initialization)
  3. Guard shared ones with locks if they are not readonly vars: examples?
  4. The rest should be put into LIBTLS Structure for that lib. - but first we simply assume that we have "__thread" and mark them with this directive, maybe using a conditionaly defined macro __THREAD, depending on HAVE_THREADS. Examples: currRing, options (value/test)...
  5. Each lib should provide its own Init/Done_lib global functions that are supposed to know about corresponding functions for underlying libraries, and should call them in correct order: easy with the left libraries(?)
  6. Each library should have its own TLS macro and access thread local variables via: TLS().variable