Add Plan 9-style barriers

Plan 9 has a very interesting synchronization mechanism, the
rendezvous() call. A good property of this is that you don't need to
explicitly initialize and destroy a barrier object, unlike as with e.g.
POSIX barriers (which are mandatory to begin with). Upon "meeting", they
can exchange a value.

This mechanism will be nice to synchronize certain stages of
initialization between threads in the following commit.

Unlike Plan 9 rendezvous(), this is not implemented with a hashtable,
because that would require additional effort (especially if you want to
make it actually scele). Unlike the Plan 9 variant, we use intptr_t
instead of void* as type for the value, because I expect that we will be
mostly passing a status code as value and not a pointer. Converting an
integer to void* requires two cast (because the integer needs to be
intptr_t), the other way around it's only one cast.

We don't particularly care about performance in this case either. It's
simply not important for our use-case. So a simple linked list is used
for waiters, and on wakeup, all waiters are temporarily woken up.

1 files changed, 1 insertions, 0 deletions

diff --git a/old-makefile b/old-makefile
index c5d8e6a223..a1d98e60ec 100644
--- a/old-makefile
+++ b/old-makefile
@@ -177,6 +177,7 @@ SOURCES = audio/audio.c \
           input/keycodes.c \
           misc/charset_conv.c \
           misc/dispatch.c \
+          misc/rendezvous.c \
           misc/ring.c \
           options/m_config.c \
           options/m_option.c \