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Multithreading
==============
is currently being developed and does not work yet.
Installation
------------
In the Makefile, define in the CFLAGS the symbol MULTITHREAD and one of
the symbols POSIX_THREADS, POSIXOLD_THREADS, SOLARIS_THREADS, C_THREADS,
WIN32_THREADS. (See xthread.d about their meaning.)
Symbol values
-------------
Any symbol can be in one of five states:
- Global Variable. This means that SYMBOL-VALUE of the symbol accesses
the same value cell for all threads.
- Global Constant. This is the same as Global Variable, except that the
value cell cannot be modified. And the compiler can optimize this kind
of symbols.
- Per-Thread Variable. This means that every thread has its private value
cell which is accessed by SYMBOL-VALUE. LET/LET*/MULTIPLE-VALUE-BIND
bindings of the variable will affect the lexical environment only, not
the value cell, unless the variable is locally declared SPECIAL.
- Per-Thread Special Variable. This means that every thread has its private
value cell which is accessed by SYMBOL-VALUE. LET/LET*/MULTIPLE-VALUE-BIND
bindings of the variable will affect this value cell.
- Lazy. This is the initial state of the symbol. It lasts until
- a DEFGLOBAL or DEFCONSTANT declaration for the symbol is evaluated,
in which case the symbol becomes a Global Variable or a Global Constant,
or
- a SPECIAL proclamation for the symbol is evaluated,
in which case the symbol becomes a Per-Thread Special Variable,
or
- a SYMBOL-VALUE reference for the symbol is evaluated,
in which case the symbol becomes a Per-Thread Variable.
Once a symbol is Global or Per-Thread, this cannot change any more.
However, a Global Variable can become a Global Constant (by means of a
DEFCONSTANT declaration), and a Per-Thread Variable can become a
Per-Thread Special Variable (by means of a SPECIAL proclamation).
The Common Lisp standard variables are all Per-Thread, except *features* and
*modules*, which are Global.
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