Julian Seward 30199fec47 In accordance with "build one to throw away, you will anyway (tm)", ...

throw away the old signals simulation and more or less start again
from scratch.  vg_signals.c is nearly a complete rewrite.  In fact
this is now the third generation of the signals simulation.

The purpose of this is to properly support signals in threads -- a
nightmare combination.  pthread_sigmask, pthread_kill and sigwait
are now alledged to work as POSIX requires.

In the process, throw away confusing and conceptually muddled old
implementation and replace with something which is more verbose but
conceptually cleaner, simpler and easier to argue is correct.

* When the client does sigaction/sigprocmask et al, the resulting
  changes are stored verbatim in SCSS -- the Static Client Signal State.
  So SCSS is the state the client believes the kernel is in.

* Every time SCSS changes, we recalculate the state the kernel
  *should* be in so that our signal simulation works.  This is the
  SKSS -- Static Kernel Signal State.  The kernel state is then
  updated accordingly.  By diffing the new and old SKSSs, the
  number of real system calls made is minimised.

* The dynamic state of the client's signals is stored in DCSS
  -- Dynamic Client Signal State.  This just records which signals
  are pending for which threads.

The big advantage of this scheme over the previous is that the SCSS ->
SKSS mapping is made explicit and gathered all in one place, rather
than spread out in a confusing way and done implicitly.  That makes it
all lot easier to decide if the mapping, which is really the heart of
the signals simulation, is correct or not.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@271

2002-05-15 21:13:39 +00:00

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