[incubator-age] branch master updated: Fix VLE local cache bug (crash)

[jgemignani]

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jgemignani pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/incubator-age.git


The following commit(s) were added to refs/heads/master by this push:
     new d5cd568  Fix VLE local cache bug (crash)
d5cd568 is described below

commit d5cd56883da75bcf6d85f85b71f169cc5421a325
Author: John Gemignani <jrgemign...@gmail.com>
AuthorDate: Thu May 26 13:49:19 2022 -0700

    Fix VLE local cache bug (crash)
    
    Fixed the VLE local cache. It had a bug that caused a circular loop
    in the LRU cache list. This loop would then cause a crash when the
    cache attempted to purge off old entries.
    
    No impact on regression tests.
---
 src/backend/utils/adt/age_vle.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/backend/utils/adt/age_vle.c b/src/backend/utils/adt/age_vle.c
index 30c7397..35d7e71 100644
--- a/src/backend/utils/adt/age_vle.c
+++ b/src/backend/utils/adt/age_vle.c
@@ -149,7 +149,7 @@ static void cache_VLE_local_context(VLE_local_context 
*vlelctx);
 static VLE_local_context *get_cached_VLE_local_context(int64 
vle_grammar_node_id)
 {
     VLE_local_context *vlelctx = global_vle_local_contexts;
-    VLE_local_context *prev = global_vle_local_contexts;
+    VLE_local_context *prev = NULL;
     VLE_local_context *next = NULL;
     int cache_size = 0;
 
@@ -162,10 +162,16 @@ static VLE_local_context 
*get_cached_VLE_local_context(int64 vle_grammar_node_id
             /* set the next pointer to the context that follows */
             next = vlelctx->next;
 
-            /* clear (unlink) the previous context's next pointer, if needed */
+            /*
+             * Clear (unlink) the previous context's next pointer, if needed.
+             * Also clear prev as we are at the end of avaiable cached contexts
+             * and just purging them off. Remember, this forms a loop that will
+             * exit the while after purging.
+             */
             if (prev != NULL)
             {
                 prev->next = NULL;
+                prev = NULL;
             }
 
             /* free the context */
@@ -217,7 +223,7 @@ static VLE_local_context 
*get_cached_VLE_local_context(int64 vle_grammar_node_id
                  * If the context is good and isn't at the head of the cache,
                  * promote it to the head.
                  */
-                if (ggctx != NULL && vlelctx != prev)
+                if (ggctx != NULL && vlelctx != global_vle_local_contexts)
                 {
                     /* adjust the links to cut out the node */
                     prev->next = vlelctx->next;