Don't share cached Lexotics over threads.

Doing so leads to a race on the result slot, which can cause all kinds
of trouble.

src/6model/reprs/MVMStaticFrame.c

@@ -140,13 +140,6 @@ static void gc_mark(MVMThreadContext *tc, MVMSTable *st, void *data, MVMGCWorkli
                 MVM_gc_worklist_add(tc, worklist, &body->static_env[i].o);
     }
 
-    /* Lexotics cache. */
-    if (body->num_lexotics) {
-        MVMint32 i;
-        for (i = 0; i < body->num_lexotics; i++)
-            MVM_gc_worklist_add(tc, worklist, &body->lexotics[i]);
-    }
-
     /* Spesh slots. */
     if (body->num_spesh_candidates) {
         MVMint32 i, j;

src/6model/reprs/MVMStaticFrame.h

@@ -61,10 +61,6 @@ struct MVMStaticFrameBody {
     /* The number of exception handlers this frame has. */
     MVMuint32 num_handlers;
 
-    /* Lexotics cache. */
-    MVMint32 num_lexotics;
-    MVMLexotic **lexotics;
-
     /* The compilation unit unique ID of this frame. */
     MVMString *cuuid;
 

src/core/exceptions.c

@@ -528,24 +528,29 @@ MVMObject * MVM_exception_newlexotic(MVMThreadContext *tc, MVMuint32 offset) {
         MVM_exception_throw_adhoc(tc, "Label with no handler passed to newlexotic");
 
     /* See if we've got this lexotic cached; return it if so. */
-    lexotic = NULL;
-    for (i = 0; i < sf->body.num_lexotics; i++)
-        if (sf->body.lexotics[i]->body.handler_idx == handler_idx)
-            return (MVMObject *)sf->body.lexotics[i];
+    if (sf->body.pool_index < tc->lexotic_cache_size) {
+        lexotic = tc->lexotic_cache[sf->body.pool_index];
+        if (lexotic && lexotic->body.handler_idx == handler_idx)
+            return (MVMObject *)lexotic;
+    }
 
     /* Allocate lexotic object, set it up, and cache it. */
     MVMROOT(tc, sf, {
         lexotic = (MVMLexotic *)MVM_repr_alloc_init(tc, tc->instance->Lexotic);
     });
     lexotic->body.handler_idx = handler_idx;
     MVM_ASSIGN_REF(tc, &(lexotic->common.header), lexotic->body.sf, sf);
-    if (sf->body.num_lexotics)
-        sf->body.lexotics = realloc(sf->body.lexotics,
-            (sf->body.num_lexotics + 1) * sizeof(MVMLexotic *));
-    else
-        sf->body.lexotics = malloc(sizeof(MVMLexotic *));
-    MVM_ASSIGN_REF(tc, &(sf->common.header), sf->body.lexotics[sf->body.num_lexotics], lexotic);
-    sf->body.num_lexotics++;
+    if (sf->body.pool_index >= tc->lexotic_cache_size) {
+        MVMuint32 orig_size = tc->lexotic_cache_size;
+        tc->lexotic_cache_size = sf->body.pool_index + 1;
+        tc->lexotic_cache = orig_size
+            ? realloc(tc->lexotic_cache, tc->lexotic_cache_size * sizeof(MVMLexotic *))
+            : malloc(tc->lexotic_cache_size * sizeof(MVMLexotic *));
+        memset(tc->lexotic_cache + orig_size, 0,
+            (tc->lexotic_cache_size - orig_size) * sizeof(MVMLexotic *));
+    }
+    if (!tc->lexotic_cache[sf->body.pool_index])
+        tc->lexotic_cache[sf->body.pool_index] = lexotic;
 
     return (MVMObject *)lexotic;
 }

src/core/threadcontext.h

@@ -161,8 +161,15 @@ struct MVMThreadContext {
     /* Pool table of chains of frames for each static frame. */
     MVMFrame **frame_pool_table;
 
-    /* Size of the pool table, so it can grow on demand. */
-    MVMuint32          frame_pool_table_size;
+    /* Pool of Lexotics for various static frames, held per thread since the
+     * result being returned is per thread. Indexes are same as used in the
+     * frame_pool_table above. */
+    MVMLexotic **lexotic_cache;
+
+    /* Size of the frame pool table and lexotic cache, so they can grow on
+     * demand. */
+    MVMuint32 frame_pool_table_size;
+    MVMuint32 lexotic_cache_size;
 
     /* Serialization context write barrier disabled depth (anything non-zero
      * means disabled). */

src/gc/roots.c

@@ -87,6 +87,14 @@ void MVM_gc_root_add_tc_roots_to_worklist(MVMThreadContext *tc, MVMGCWorklist *w
     if (tc->interp_cu)
         MVM_gc_worklist_add(tc, worklist, tc->interp_cu);
 
+    /* Lexotics cache. */
+    if (tc->lexotic_cache_size) {
+        MVMuint32 i;
+        for (i = 0; i < tc->lexotic_cache_size; i++)
+            if (tc->lexotic_cache[i])
+                MVM_gc_worklist_add(tc, worklist, &(tc->lexotic_cache[i]));
+    }
+
     /* Current dispatcher. */
     MVM_gc_worklist_add(tc, worklist, &tc->cur_dispatcher);