[pypy-svn] r22993 - pypy/dist/pypy/lib/logic

[auc at codespeak.net]

Author: auc
Date: Fri Feb  3 17:18:51 2006
New Revision: 22993

Added:
   pypy/dist/pypy/lib/logic/oz-dataflow-concurrency.txt
Log:
embryonic document about oz threading model, dataflow concurrency, etc. which forms a basis of concurrent constraint programming ; implementors of threads/coroutines in pyyp (C. Tismer & al might want to read this and comment)


Added: pypy/dist/pypy/lib/logic/oz-dataflow-concurrency.txt
==============================================================================
--- (empty file)
+++ pypy/dist/pypy/lib/logic/oz-dataflow-concurrency.txt	Fri Feb  3 17:18:51 2006
@@ -0,0 +1,73 @@
+Some rough notes about the Oz threading model
+=============================================
+
+Scheduling
+----------
+
+Fair scheduling through round-robin.
+
+Needs not be deterministic (would be nice, especially when debugging,
+but probably impossible to achieve).
+
+With priority levels : three queues exist, which manage high, medium,
+low priority threads. The time slice ratio for these is
+100:10:1. Threads inherit the priority of their parent.
+
+Mozart uses an external timer approach to implement thread preemption.
+
+Thread ops
+----------
+
+All these ops are defined in a Thread namespace/module.
+
+this()               -> current thread's name (*not* another thread's name)
+state(t)             -> return state of t in {runnable, blocked, terminated}
+suspend(t)            : suspend t
+resume(t)             : resume execution of t
+preempt(t)            : preempt t
+terminate(t)          : terminate t immediately
+injectException(t, e) : raise exception e in t
+setPriority(t, p)     : set t's priority to p
+
+Interestingly, coroutines can be build upon this thread
+API. Coroutines have two ops : spawn and resume.
+
+spawn(p)             -> creates a coroutine with procedure p, returns pid
+resume(c)             : transfers control from current coroutine to c
+
+The implementation of these ops in terms of the threads API is as
+follows :
+
+def spawn(p):
+    in_thread:
+        pid = Thread.this()
+        Thread.suspend(pid)
+        p()
+
+def resume(cid):
+    Thread.resume cid
+    Thread.suspend(Thread.this())
+
+
+Thread communication
+--------------------
+
+No shared state is allowed (in the model we are interested in
+anyway). Threads communicate through dataflow variables, which
+alleviates the need for explicit locking/monitoring.
+
+While this restricts somewhat what can be done, it is the most
+expressive way of using threads without shooting oneself in the
+foot. Concurrent constraint programming uses and abuses of this kind
+of concurrency.
+
+Dataflow variable allow streams to be created. "A stream is a
+potentially unbounded list of messages, i.e a list whose tail is an
+unbound dataflow variable. Receiving a message is reading a stream
+element. Each variable is bound by only one thread".
+
+If you practice UNIX pipes, you know what all this is about. Also see
+http://www.jpaulmorrison.com/fbp/.
+
+
+[more to come]
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