From dc3841fe45692ab1cda05625f74d951a5a0460d7 Mon Sep 17 00:00:00 2001
From: dkf <donal.k.fellows@manchester.ac.uk>
Date: Mon, 16 May 2016 10:57:36 +0000
Subject: Possible fix for [f97d4ee020]; uses a two-stage approach to avoid
 quadratic behaviour.

---
 generic/tclNamesp.c | 76 +++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 53 insertions(+), 23 deletions(-)

diff --git a/generic/tclNamesp.c b/generic/tclNamesp.c
index dfab185..d286de4 100644
--- a/generic/tclNamesp.c
+++ b/generic/tclNamesp.c
@@ -1105,8 +1105,6 @@ TclTeardownNamespace(
     Interp *iPtr = (Interp *) nsPtr->interp;
     register Tcl_HashEntry *entryPtr;
     Tcl_HashSearch search;
-    Tcl_Namespace *childNsPtr;
-    Tcl_Command cmd;
     int i;
 
     /*
@@ -1121,16 +1119,27 @@ TclTeardownNamespace(
     /*
      * Delete all commands in this namespace. Be careful when traversing the
      * hash table: when each command is deleted, it removes itself from the
-     * command table.
-     *
-     * Don't optimize to Tcl_NextHashEntry() because of traces.
+     * command table. Because of traces (and the desire to avoid the quadratic
+     * problems of just using Tcl_FirstHashEntry over and over, [Bug
+     * f97d4ee020]) we copy to a temporary array and then delete all those
+     * commands.
      */
 
-    for (entryPtr = Tcl_FirstHashEntry(&nsPtr->cmdTable, &search);
-	    entryPtr != NULL;
-	    entryPtr = Tcl_FirstHashEntry(&nsPtr->cmdTable, &search)) {
-	cmd = Tcl_GetHashValue(entryPtr);
-	Tcl_DeleteCommandFromToken((Tcl_Interp *) iPtr, cmd);
+    while (nsPtr->cmdTable.numEntries > 0) {
+	int length = nsPtr->cmdTable.numEntries;
+	Tcl_Command *cmds = TclStackAlloc((Tcl_Interp *) iPtr,
+		sizeof(Tcl_Command) * length);
+
+	i = 0;
+	for (entryPtr = Tcl_FirstHashEntry(&nsPtr->cmdTable, &search);
+		entryPtr != NULL;
+		entryPtr = Tcl_NextHashEntry(&search)) {
+	    cmds[i++] = Tcl_GetHashValue(entryPtr);
+	}
+	for (i = 0 ; i < length ; i++) {
+	    Tcl_DeleteCommandFromToken((Tcl_Interp *) iPtr, cmds[i]);
+	}
+	TclStackFree((Tcl_Interp *) iPtr, cmds);
     }
     Tcl_DeleteHashTable(&nsPtr->cmdTable);
     Tcl_InitHashTable(&nsPtr->cmdTable, TCL_STRING_KEYS);
@@ -1175,25 +1184,46 @@ TclTeardownNamespace(
      *
      * BE CAREFUL: When each child is deleted, it will divorce itself from its
      * parent. You can't traverse a hash table properly if its elements are
-     * being deleted. We use only the Tcl_FirstHashEntry function to be safe.
-     *
-     * Don't optimize to Tcl_NextHashEntry() because of traces.
+     * being deleted.  Because of traces (and the desire to avoid the
+     * quadratic problems of just using Tcl_FirstHashEntry over and over, [Bug
+     * f97d4ee020]) we copy to a temporary array and then delete all those
+     * namespaces.
      */
 
 #ifndef BREAK_NAMESPACE_COMPAT
-    for (entryPtr = Tcl_FirstHashEntry(&nsPtr->childTable, &search);
-	    entryPtr != NULL;
-	    entryPtr = Tcl_FirstHashEntry(&nsPtr->childTable, &search)) {
-	childNsPtr = Tcl_GetHashValue(entryPtr);
-	Tcl_DeleteNamespace(childNsPtr);
+    while (nsPtr->childTable.numEntries > 0) {
+	int length = nsPtr->childTable.numEntries;
+	Tcl_Namespace **nss = TclStackAlloc((Tcl_Interp *) iPtr,
+		sizeof(Tcl_Namespace *) * length);
+
+	i = 0;
+	for (entryPtr = Tcl_FirstHashEntry(&nsPtr->childTable, &search);
+		entryPtr != NULL;
+		entryPtr = Tcl_NextHashEntry(&search)) {
+	    nss[i++] = Tcl_GetHashValue(entryPtr);
+	}
+	for (i = 0 ; i < length ; i++) {
+	    Tcl_DeleteNamespace(nss[i]);
+	}
+	TclStackFree((Tcl_Interp *) iPtr, nss);
     }
 #else
     if (nsPtr->childTablePtr != NULL) {
-	for (entryPtr = Tcl_FirstHashEntry(nsPtr->childTablePtr, &search);
-		entryPtr != NULL;
-		entryPtr = Tcl_FirstHashEntry(nsPtr->childTablePtr,&search)) {
-	    childNsPtr = Tcl_GetHashValue(entryPtr);
-	    Tcl_DeleteNamespace(childNsPtr);
+	while (nsPtr->childTablePtr->numEntries > 0) {
+	    int length = nsPtr->childTablePtr->numEntries;
+	    Tcl_Namespace **nss = TclStackAlloc((Tcl_Interp *) iPtr,
+		    sizeof(Tcl_Namespace *) * length);
+
+	    i = 0;
+	    for (entryPtr = Tcl_FirstHashEntry(nsPtr->childTablePtr, &search);
+		    entryPtr != NULL;
+		    entryPtr = Tcl_NextHashEntry(&search)) {
+		nss[i++] = Tcl_GetHashValue(entryPtr);
+	    }
+	    for (i = 0 ; i < length ; i++) {
+		Tcl_DeleteNamespace(nss[i]);
+	    }
+	    TclStackFree((Tcl_Interp *) iPtr, nss);
 	}
     }
 #endif
-- 
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