[pypy-commit] extradoc extradoc: First-step planning.

arigo noreply at buildbot.pypy.org
Tue Jan 31 18:57:10 CET 2012

Author: Armin Rigo <arigo at tunes.org>
Branch: extradoc
Changeset: r4070:9e7b09df3f36
Date: 2012-01-31 18:56 +0100

Log:	First-step planning.

diff --git a/planning/stm.txt b/planning/stm.txt
--- a/planning/stm.txt
+++ b/planning/stm.txt
@@ -2,6 +2,9 @@
 STM planning
+Comments in << >> describe the next thing to work on.
@@ -72,6 +75,9 @@
 use 4-5 bits, where in addition we use some "thread hash" value if there
 is only one copy.
+<< NOW: think of a minimal GC model with these properties.  We probably
+need GC_GLOBAL, a single bit of GC_WAS_COPIED, and the version number. >>
@@ -96,6 +102,10 @@
   depending on cases).  And if the read is accepted then we need to
   remember in a local list that we've read that object.
+<< NOW: implement the thread's local dictionary in C, as say a search
+tree.  Should be easy enough if we don't try to be as efficient as
+possible.  The rest of the logic here is straightforward. >>
@@ -114,6 +124,8 @@
 consistent copy (i.e. nobody changed the object in the middle of us
 reading it).  If it is too recent, then we might have to abort.
+<< NOW: straightforward >>
 End-of-transaction collections
@@ -132,6 +144,9 @@
 We need to check that each of these global objects' versions have not
 been modified in the meantime.
+<< NOW: should be easy, but with unclear interactions between the C
+code and the GC. >>
 Annotator support
@@ -149,6 +164,8 @@
 of a localobj are themselves localobjs.  This would be useful for
 'PyFrame.fastlocals_w': it should also be known to always be a localobj.
+<< do later >>
 Local collections
@@ -173,6 +190,9 @@
 all global reads done --- "compress" in the sense of removing
+<< do later; memory usage grows unboundedly during one transaction for
+now. >>
 Global collections
@@ -218,6 +238,10 @@
 * Parallelism: there are multiple threads all doing something GC-related,
   like all scanning the heap together.
+<< at first the global area keeps growing unboundedly.  The next step
+will be to add the LIL but run the global collection by keeping all
+other threads blocked. >>
 When not running transactively
@@ -240,11 +264,11 @@
 is called, we can try to do such a collection, but what about the pinned
-Some intermediate solution would be to let this mode be rather slow:
+<< NOW: let this mode be rather slow.  To implement this mode, we would
 have only global objects, and have the stm_write barrier of 'obj' return
-'obj'.  Do only global collections.  Allocation would allocate
-immediately a global object, mostly without being able to benefit from
-bump-pointer allocation.
+'obj'.  Do only global collections (one we have them; at first, don't
+collect at all).  Allocation would allocate immediately a global object,
+without being able to benefit from bump-pointer allocation. >>
 Pointer equality
@@ -261,6 +285,8 @@
 dictionary if they map to each other.  And we need to take care of the
 cases of NULL pointers.
+<< NOW: straightforward, if we're careful not to forget cases >>

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