[pypy-commit] stmgc use-gcc: just a test showing that entries may stay alive (gc-wise) but get thrown out of the hashtable

[Raemi]

Author: Remi Meier <remi.meier at inf.ethz.ch>
Branch: use-gcc
Changeset: r1955:c2f312c07ed8
Date: 2015-09-08 14:42 +0200
http://bitbucket.org/pypy/stmgc/changeset/c2f312c07ed8/

Log:	just a test showing that entries may stay alive (gc-wise) but get
	thrown out of the hashtable

diff --git a/c8/stm/hashtable.c b/c8/stm/hashtable.c
--- a/c8/stm/hashtable.c
+++ b/c8/stm/hashtable.c
@@ -180,6 +180,8 @@
         char *to_read_from = segment_base;
         if (segnum != -1) {
             /* -> compaction during major GC */
+            /* it's possible that we just created this entry, and it wasn't
+               touched in this segment yet. Then seg0 is up-to-date.  */
             to_read_from = get_page_status_in(segnum, (uintptr_t)entry / 4096UL) == PAGE_NO_ACCESS
                 ? stm_object_pages : to_read_from;
             if (((struct stm_hashtable_entry_s *)
@@ -359,7 +361,7 @@
                              uintptr_t key)
 {
     stm_hashtable_entry_t *e = stm_hashtable_lookup(hobj, hashtable, key);
-    stm_read((object_t *)e);
+    // stm_read((object_t *)e); - done in _lookup()
     return e->object;
 }
 
diff --git a/c8/test/test_hashtable.py b/c8/test/test_hashtable.py
--- a/c8/test/test_hashtable.py
+++ b/c8/test/test_hashtable.py
@@ -423,6 +423,38 @@
         stm_major_collect()
         self.commit_transaction()
 
+    def test_empty_entry_not_kept_alive(self):
+        self.start_transaction()
+        h = self.allocate_hashtable()
+        self.push_root(h)
+        stm_minor_collect()
+        h = self.pop_root()
+        self.push_root(h)
+
+        # produce some entries so we get compaction in major GC
+        K = 300
+        for i in range(K):
+            hashtable_lookup(h, get_hashtable(h), i)
+
+        entry = hashtable_lookup(h, get_hashtable(h), K)
+        self.push_root(entry)
+
+        self.commit_transaction()
+        self.start_transaction()
+
+        stm_major_collect() # compaction and rehashing
+
+        entry = self.pop_root()
+        entry2 = hashtable_lookup(h, get_hashtable(h), K)
+        assert entry != entry2
+
+        # get rid of ht:
+        self.pop_root()
+        self.commit_transaction()
+        self.start_transaction()
+        stm_major_collect()
+        self.commit_transaction()
+