diff --git a/opengl/libs/GLES2_dbg/generate_debugger_message_proto.py b/opengl/libs/GLES2_dbg/generate_debugger_message_proto.py
index 914ea24..57e008c 100755
--- a/opengl/libs/GLES2_dbg/generate_debugger_message_proto.py
+++ b/opengl/libs/GLES2_dbg/generate_debugger_message_proto.py
@@ -142,6 +142,7 @@
         TimeMode = 1; // arg0 = SYSTEM_TIME_* in utils/Timers.h
         ExpectResponse = 2; // arg0 = enum Function, arg1 = true/false
         CaptureSwap = 3; // arg0 = number of eglSwapBuffers to glReadPixels
+        GLConstant = 4; // arg0 = GLenum, arg1 = constant; send GL impl. constants
     };
     optional Prop prop = 21; // used with SETPROP, value in arg0
     optional float clock = 22; // wall clock in seconds
diff --git a/opengl/libs/GLES2_dbg/src/dbgcontext.cpp b/opengl/libs/GLES2_dbg/src/dbgcontext.cpp
index 71892d3..7f5b27b 100644
--- a/opengl/libs/GLES2_dbg/src/dbgcontext.cpp
+++ b/opengl/libs/GLES2_dbg/src/dbgcontext.cpp
@@ -71,7 +71,24 @@
     GLint readFormat, readType;
     hooks->gl.glGetIntegerv(GL_IMPLEMENTATION_COLOR_READ_FORMAT, &readFormat);
     hooks->gl.glGetIntegerv(GL_IMPLEMENTATION_COLOR_READ_TYPE, &readType);
-    return new DbgContext(version, hooks, MAX_VERTEX_ATTRIBS, readFormat, readType);
+    DbgContext * const dbg = new DbgContext(version, hooks, MAX_VERTEX_ATTRIBS, readFormat, readType);
+
+    glesv2debugger::Message msg, cmd;
+    msg.set_context_id(reinterpret_cast<int>(dbg));
+    msg.set_expect_response(false);
+    msg.set_type(msg.Response);
+    msg.set_function(msg.SETPROP);
+    msg.set_prop(msg.GLConstant);
+    msg.set_arg0(GL_MAX_VERTEX_ATTRIBS);
+    msg.set_arg1(MAX_VERTEX_ATTRIBS);
+    Send(msg, cmd);
+
+    GLint MAX_COMBINED_TEXTURE_IMAGE_UNITS = 0;
+    hooks->gl.glGetIntegerv(GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS, &MAX_COMBINED_TEXTURE_IMAGE_UNITS);
+    msg.set_arg0(GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS);
+    msg.set_arg1(MAX_COMBINED_TEXTURE_IMAGE_UNITS);
+    Send(msg, cmd);
+    return dbg;
 }
 
 void DestroyDbgContext(DbgContext * const dbg)
diff --git a/opengl/libs/GLES2_dbg/src/debugger_message.pb.cpp b/opengl/libs/GLES2_dbg/src/debugger_message.pb.cpp
index 40478c3..50f70f7 100644
--- a/opengl/libs/GLES2_dbg/src/debugger_message.pb.cpp
+++ b/opengl/libs/GLES2_dbg/src/debugger_message.pb.cpp
@@ -477,6 +477,7 @@
     case 1:
     case 2:
     case 3:
+    case 4:
       return true;
     default:
       return false;
@@ -488,6 +489,7 @@
 const Message_Prop Message::TimeMode;
 const Message_Prop Message::ExpectResponse;
 const Message_Prop Message::CaptureSwap;
+const Message_Prop Message::GLConstant;
 const Message_Prop Message::Prop_MIN;
 const Message_Prop Message::Prop_MAX;
 const int Message::Prop_ARRAYSIZE;
@@ -975,7 +977,7 @@
         if (input->ExpectTag(208)) goto parse_image_width;
         break;
       }
-
+      
       // optional int32 image_width = 26;
       case 26: {
         if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
@@ -991,7 +993,7 @@
         if (input->ExpectTag(216)) goto parse_image_height;
         break;
       }
-
+      
       // optional int32 image_height = 27;
       case 27: {
         if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
@@ -1139,12 +1141,12 @@
   if (_has_bit(18)) {
     ::google::protobuf::internal::WireFormatLite::WriteInt32(26, this->image_width(), output);
   }
-
+  
   // optional int32 image_height = 27;
   if (_has_bit(19)) {
     ::google::protobuf::internal::WireFormatLite::WriteInt32(27, this->image_height(), output);
   }
-
+  
 }
 
 int Message::ByteSize() const {
@@ -1282,14 +1284,14 @@
         ::google::protobuf::internal::WireFormatLite::Int32Size(
           this->image_width());
     }
-
+    
     // optional int32 image_height = 27;
     if (has_image_height()) {
       total_size += 2 +
         ::google::protobuf::internal::WireFormatLite::Int32Size(
           this->image_height());
     }
-
+    
     // optional float time = 11;
     if (has_time()) {
       total_size += 1 + 4;
diff --git a/opengl/libs/GLES2_dbg/src/debugger_message.pb.h b/opengl/libs/GLES2_dbg/src/debugger_message.pb.h
index 4ccfebb..5c94664 100644
--- a/opengl/libs/GLES2_dbg/src/debugger_message.pb.h
+++ b/opengl/libs/GLES2_dbg/src/debugger_message.pb.h
@@ -258,11 +258,12 @@
   Message_Prop_CaptureDraw = 0,
   Message_Prop_TimeMode = 1,
   Message_Prop_ExpectResponse = 2,
-  Message_Prop_CaptureSwap = 3
+  Message_Prop_CaptureSwap = 3,
+  Message_Prop_GLConstant = 4
 };
 bool Message_Prop_IsValid(int value);
 const Message_Prop Message_Prop_Prop_MIN = Message_Prop_CaptureDraw;
-const Message_Prop Message_Prop_Prop_MAX = Message_Prop_CaptureSwap;
+const Message_Prop Message_Prop_Prop_MAX = Message_Prop_GLConstant;
 const int Message_Prop_Prop_ARRAYSIZE = Message_Prop_Prop_MAX + 1;
 
 // ===================================================================
@@ -544,6 +545,7 @@
   static const Prop TimeMode = Message_Prop_TimeMode;
   static const Prop ExpectResponse = Message_Prop_ExpectResponse;
   static const Prop CaptureSwap = Message_Prop_CaptureSwap;
+  static const Prop GLConstant = Message_Prop_GLConstant;
   static inline bool Prop_IsValid(int value) {
     return Message_Prop_IsValid(value);
   }
@@ -691,14 +693,14 @@
   static const int kImageWidthFieldNumber = 26;
   inline ::google::protobuf::int32 image_width() const;
   inline void set_image_width(::google::protobuf::int32 value);
-
+  
   // optional int32 image_height = 27;
   inline bool has_image_height() const;
   inline void clear_image_height();
   static const int kImageHeightFieldNumber = 27;
   inline ::google::protobuf::int32 image_height() const;
   inline void set_image_height(::google::protobuf::int32 value);
-
+  
   // optional float time = 11;
   inline bool has_time() const;
   inline void clear_time();
diff --git a/opengl/libs/GLES2_dbg/src/server.cpp b/opengl/libs/GLES2_dbg/src/server.cpp
index ba4960d..0c711bf 100644
--- a/opengl/libs/GLES2_dbg/src/server.cpp
+++ b/opengl/libs/GLES2_dbg/src/server.cpp
@@ -159,8 +159,17 @@
 
 float Send(const glesv2debugger::Message & msg, glesv2debugger::Message & cmd)
 {
+    // TODO: use per DbgContext send/receive buffer and async socket
+    //  instead of mutex and blocking io; watch out for large messages
     static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
-    pthread_mutex_lock(&mutex); // TODO: this is just temporary
+    struct Autolock {
+        Autolock() {
+            pthread_mutex_lock(&mutex);
+        }
+        ~Autolock() {
+            pthread_mutex_unlock(&mutex);
+        }
+    } autolock;
 
     if (msg.function() != glesv2debugger::Message_Function_ACK)
         assert(msg.has_context_id() && msg.context_id() != 0);
@@ -176,7 +185,6 @@
                 Die("MAX_FILE_SIZE reached");
             }
         }
-        pthread_mutex_unlock(&mutex);
         return 0;
     }
     int sent = -1;
@@ -192,7 +200,11 @@
         LOGD("actual sent=%d expected=%d clientSock=%d", sent, str.length(), clientSock);
         Die("Failed to send message");
     }
-
+    // TODO: factor Receive & TryReceive out and into MessageLoop, or add control argument.
+    // mean while, if server is sending a SETPROP then don't try to receive,
+    //  because server will not be processing received command
+    if (msg.function() == msg.SETPROP)
+        return t;
     // try to receive commands even though not expecting response,
     //  since client can send SETPROP and other commands anytime
     if (!msg.expect_response()) {
@@ -204,8 +216,6 @@
         }
     } else
         Receive(cmd);
-
-    pthread_mutex_unlock(&mutex);
     return t;
 }
 
diff --git a/opengl/libs/GLES2_dbg/test/test_server.cpp b/opengl/libs/GLES2_dbg/test/test_server.cpp
index 7fb87ea..b6401e0 100644
--- a/opengl/libs/GLES2_dbg/test/test_server.cpp
+++ b/opengl/libs/GLES2_dbg/test/test_server.cpp
@@ -60,10 +60,14 @@
         msg.ParseFromArray(buffer, len);
         delete buffer;
     }
+
+    void CheckNoAvailable() {
+        const long pos = ftell(file);
+        fseek(file, 0, SEEK_END);
+        EXPECT_EQ(pos, ftell(file)) << "check no available";
+    }
 };
 
-
-
 TEST_F(ServerFileTest, Send)
 {
     glesv2debugger::Message msg, cmd, read;
@@ -81,6 +85,56 @@
     EXPECT_EQ(msg.type(), read.type());
 }
 
+TEST_F(ServerFileTest, CreateDbgContext)
+{
+    gl_hooks_t hooks;
+    struct Constant {
+        GLenum pname;
+        GLint param;
+    };
+    static const Constant constants [] = {
+        {GL_MAX_VERTEX_ATTRIBS, 16},
+        {GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS, 32},
+        {GL_IMPLEMENTATION_COLOR_READ_FORMAT, GL_RGBA},
+        {GL_IMPLEMENTATION_COLOR_READ_TYPE, GL_UNSIGNED_BYTE},
+    };
+    struct HookMock {
+        static void GetIntegerv(GLenum pname, GLint* params) {
+            ASSERT_TRUE(params != NULL);
+            for (unsigned int i = 0; i < sizeof(constants) / sizeof(*constants); i++)
+                if (pname == constants[i].pname) {
+                    *params = constants[i].param;
+                    return;
+                }
+            FAIL() << "GetIntegerv unknown pname: " << pname;
+        }
+        static GLenum GetError() {
+            return GL_NO_ERROR;
+        }
+    };
+    hooks.gl.glGetError = HookMock::GetError;
+    hooks.gl.glGetIntegerv = HookMock::GetIntegerv;
+    DbgContext * const dbg = CreateDbgContext(-1, 1, &hooks);
+    ASSERT_TRUE(dbg != NULL);
+    EXPECT_TRUE(dbg->vertexAttribs != NULL);
+
+    rewind(file);
+    glesv2debugger::Message read;
+    for (unsigned int i = 0; i < 2; i++) {
+        Read(read);
+        EXPECT_EQ(reinterpret_cast<int>(dbg), read.context_id());
+        EXPECT_FALSE(read.expect_response());
+        EXPECT_EQ(read.Response, read.type());
+        EXPECT_EQ(read.SETPROP, read.function());
+        EXPECT_EQ(read.GLConstant, read.prop());
+        GLint expectedConstant = 0;
+        HookMock::GetIntegerv(read.arg0(), &expectedConstant);
+        EXPECT_EQ(expectedConstant, read.arg1());
+    }
+    CheckNoAvailable();
+    DestroyDbgContext(dbg);
+}
+
 void * glNoop()
 {
     return 0;
diff --git a/opengl/libs/GLES2_dbg/test/test_socket.cpp b/opengl/libs/GLES2_dbg/test/test_socket.cpp
index 1c31a94..617292e 100644
--- a/opengl/libs/GLES2_dbg/test/test_socket.cpp
+++ b/opengl/libs/GLES2_dbg/test/test_socket.cpp
@@ -50,7 +50,7 @@
             pthread_key_create(&dbgEGLThreadLocalStorageKey, NULL);
         ASSERT_NE(-1, dbgEGLThreadLocalStorageKey);
         tls.dbg = new DbgContext(1, &hooks, 32, GL_RGBA, GL_UNSIGNED_BYTE);
-        ASSERT_NE((void *)NULL, tls.dbg);
+        ASSERT_TRUE(tls.dbg != NULL);
         pthread_setspecific(dbgEGLThreadLocalStorageKey, &tls);
         for (unsigned int i = 0; i < sizeof(hooks) / sizeof(void *); i++)
             ((void **)&hooks)[i] = (void *)glNoop;
@@ -95,7 +95,7 @@
         if (len > bufferSize) {
             bufferSize = len;
             buffer = new char[bufferSize];
-            ASSERT_NE((char *)NULL, buffer);
+            ASSERT_TRUE(buffer != NULL);
         }
         ASSERT_EQ(len, recv(sock, buffer, len, 0));
         msg.Clear();
@@ -427,7 +427,7 @@
             EXPECT_EQ(_height, height);
             EXPECT_EQ(GL_RGBA, format);
             EXPECT_EQ(GL_UNSIGNED_BYTE, type);
-            ASSERT_NE((void *)NULL, pixels);
+            ASSERT_TRUE(pixels != NULL);
             memcpy(pixels, _pixels, sizeof(_pixels));
             readPixels++;
         }