From 65058cfb7ac07204cbd2dcdc05e845a447fc54f8 Mon Sep 17 00:00:00 2001
From: Yu Yang <yuyang18@baidu.com>
Date: Fri, 23 Feb 2018 12:58:32 +0800
Subject: [PATCH] Change DFS to BFS

---
 paddle/fluid/framework/block_desc.cc | 38 +++++++++++++++--------
 python/paddle/v2/fluid/framework.py  | 46 ++++++++++++++++------------
 2 files changed, 51 insertions(+), 33 deletions(-)

diff --git a/paddle/fluid/framework/block_desc.cc b/paddle/fluid/framework/block_desc.cc
index 996aefd0479..1efb775cdca 100644
--- a/paddle/fluid/framework/block_desc.cc
+++ b/paddle/fluid/framework/block_desc.cc
@@ -16,6 +16,8 @@ limitations under the License. */
 #include "paddle/fluid/framework/operator.h"
 #include "paddle/fluid/framework/program_desc.h"
 
+#include <queue>
+
 namespace paddle {
 namespace framework {
 
@@ -45,23 +47,33 @@ bool BlockDesc::HasVar(const std::string &name) const {
 VarDesc *BlockDesc::FindVarRecursive(const std::string &name) const {
   if (name == kEmptyVarName) return nullptr;
 
-  auto it = vars_.find(name);
-  if (it != vars_.end()) {
-    return it->second.get();
-  }
+  std::queue<const BlockDesc *> frontier;
+  std::unordered_set<const BlockDesc *> visited;
 
-  BlockDesc *tmp = ParentBlock();
+  frontier.push(this);
 
-  if (tmp != nullptr) {
-    auto ptr = tmp->FindVarRecursive(name);
-    if (ptr != nullptr) {
-      return ptr;
+  while (!frontier.empty()) {  // BFS
+    auto cur = frontier.front();
+    frontier.pop();
+    if (visited.count(cur) != 0) {
+      continue;
+    }
+    auto var = cur->FindVar(name);
+    if (var != nullptr) {
+      return var;
+    }
+
+    auto fwd = cur->ForwardBlock();
+    auto parent = cur->ParentBlock();
+
+    if (fwd != nullptr) {
+      frontier.push(fwd);
+    }
+    if (parent != nullptr) {
+      frontier.push(parent);
     }
-  }
 
-  tmp = ForwardBlock();
-  if (tmp != nullptr) {
-    return tmp->FindVarRecursive(name);
+    visited.insert(cur);
   }
 
   return nullptr;
diff --git a/python/paddle/v2/fluid/framework.py b/python/paddle/v2/fluid/framework.py
index 7ec04013c91..3ec8d978140 100644
--- a/python/paddle/v2/fluid/framework.py
+++ b/python/paddle/v2/fluid/framework.py
@@ -698,26 +698,32 @@ class Block(object):
         return v
 
     def var_recursive(self, name):
-        if self.has_var(name):
-            return self.var(name)
-        else:
-            if self.idx == 0:
-                raise ValueError(
-                    "var {0} is not in block({1}) nor its parents.".format(
-                        name, self.idx))
-            else:
-                # DFS
-                try:
-                    parent_block = self.program.block(self.parent_idx)
-                    return parent_block.var_recursive(name)
-                except ValueError:
-                    fwd_block = self.program.block(
-                        self.forward_block_idx
-                    ) if self.forward_block_idx != -1 else None
-                    if fwd_block is not None:
-                        return fwd_block.var_recursive(name)
-                    else:
-                        raise
+        frontier = list()
+        visited = set()
+
+        frontier.append(self)
+
+        prog = self.program
+
+        while len(frontier) != 0:  # BFS
+            cur = frontier[0]
+            frontier = frontier[1:]
+
+            if id(cur) in visited:
+                continue
+
+            if cur.has_var(name):
+                return cur.var(name)
+
+            if cur.parent_idx != -1:
+                frontier.append(prog.block(cur.parent_idx))
+
+            if cur.forward_block_idx != -1:
+                frontier.append(prog.block(cur.forward_block_idx))
+
+            visited.add(id(cur))
+
+        raise ValueError("Var {0} is not found recursively".format(name))
 
     def all_parameters(self):
         return list(self.iter_parameters())
-- 
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