[m-rev.] diff: more stm nested transaction support

[Julien Fischer]

The following is joint work by Leon and myself.

Estimated hours taken: 0.5
Branches: main

Add more supported for nested STM transactions to the runtime.

runtime/mercury_stm.c:
 	Extend the implementations of MR_STM_validate() and MR_STM_read_var()
 	to support nested transactions.

Julien.

Index: runtime/mercury_stm.c
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/runtime/mercury_stm.c,v
retrieving revision 1.4
diff -u -r1.4 mercury_stm.c
--- runtime/mercury_stm.c	17 Sep 2007 13:28:56 -0000	1.4
+++ runtime/mercury_stm.c	21 Sep 2007 04:13:14 -0000
@@ -49,14 +49,22 @@
  {
      MR_STM_TransRecord  *current;

-    current = tlog->MR_STM_tl_records;
-    while (current != NULL) {
-        if (current->MR_STM_tr_var->MR_STM_var_value !=
-            current->MR_STM_tr_old_value)
-        {
-            return MR_STM_TRANSACTION_INVALID;
+    MR_assert(tlog != NULL);
+
+    while (tlog != NULL) {
+
+        current = tlog->MR_STM_tl_records;
+ 
+        while (current != NULL) {
+            if (current->MR_STM_tr_var->MR_STM_var_value !=
+                current->MR_STM_tr_old_value)
+            {
+                return MR_STM_TRANSACTION_INVALID;
+            }
+            current = current->MR_STM_tr_next;
          }
-        current = current->MR_STM_tr_next;
+
+        tlog = tlog->MR_STM_tl_parent;
      }

      return MR_STM_TRANSACTION_VALID;
@@ -137,20 +145,29 @@
  MR_Word
  MR_STM_read_var(MR_STM_Var *var, MR_STM_TransLog *tlog)
  {
+    MR_STM_TransLog     *current_tlog;
      MR_STM_TransRecord  *current;

-    current = tlog->MR_STM_tl_records;
-    while (current != NULL) {
-        if (current->MR_STM_tr_var == var) {
-            return current->MR_STM_tr_new_value;
+    current_tlog = tlog;
+
+    while (current_tlog != NULL) {
+ 
+        current = tlog->MR_STM_tl_records;
+        while (current != NULL) {
+            if (current->MR_STM_tr_var == var) {
+                return current->MR_STM_tr_new_value;
+            }
+            current = current->MR_STM_tr_next;
          }
-        current = current->MR_STM_tr_next;
+
+        current_tlog = current_tlog->MR_STM_tl_parent;
      }

      /*
      ** We will only get to this point if the transaction variable does not
-    ** currently have a record in the log, i.e. if this is the first time
-    ** that its value has been read during this transaction.
+    ** currently have a record in the log or one of the enclosing logs,
+    ** i.e. if this is the first time that its value has been read during
+    ** this atomic scope.
      ** Add an entry that indicates that it has been read and then return
      ** the value that is stored in the transaction variable.
      */

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