Merge remote-tracking branch 'upstream/master' into you-complete-me-csharp

10 files changed, 154 insertions, 117 deletions

diff --git a/src/core/compression/algorithm.c b/src/core/compression/algorithm.c
index ca07002ff9..36ead843d2 100644
--- a/src/core/compression/algorithm.c
+++ b/src/core/compression/algorithm.c
@@ -31,7 +31,7 @@
  *
  */
 
-#include "src/core/compression/algorithm.h"
+#include <grpc/compression.h>
 
 const char *grpc_compression_algorithm_name(
     grpc_compression_algorithm algorithm) {
diff --git a/src/core/compression/algorithm.h b/src/core/compression/algorithm.h
deleted file mode 100644
index 9dd9f57b56..0000000000
--- a/src/core/compression/algorithm.h
+++ /dev/null
@@ -1,49 +0,0 @@
-/*
- *
- * Copyright 2015, Google Inc.
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions are
- * met:
- *
- *     * Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- *     * Redistributions in binary form must reproduce the above
- * copyright notice, this list of conditions and the following disclaimer
- * in the documentation and/or other materials provided with the
- * distribution.
- *     * Neither the name of Google Inc. nor the names of its
- * contributors may be used to endorse or promote products derived from
- * this software without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- *
- */
-
-#ifndef GRPC_INTERNAL_CORE_COMPRESSION_ALGORITHM_H
-#define GRPC_INTERNAL_CORE_COMPRESSION_ALGORITHM_H
-
-/* The various compression algorithms supported by GRPC */
-typedef enum {
-  GRPC_COMPRESS_NONE = 0,
-  GRPC_COMPRESS_DEFLATE,
-  GRPC_COMPRESS_GZIP,
-  /* TODO(ctiller): snappy */
-  GRPC_COMPRESS_ALGORITHMS_COUNT
-} grpc_compression_algorithm;
-
-const char *grpc_compression_algorithm_name(
-    grpc_compression_algorithm algorithm);
-
-#endif  /* GRPC_INTERNAL_CORE_COMPRESSION_ALGORITHM_H */
diff --git a/src/core/compression/message_compress.h b/src/core/compression/message_compress.h
index e8aef1a713..aba701a6ee 100644
--- a/src/core/compression/message_compress.h
+++ b/src/core/compression/message_compress.h
@@ -34,7 +34,7 @@
 #ifndef GRPC_INTERNAL_CORE_COMPRESSION_MESSAGE_COMPRESS_H
 #define GRPC_INTERNAL_CORE_COMPRESSION_MESSAGE_COMPRESS_H
 
-#include "src/core/compression/algorithm.h"
+#include <grpc/compression.h>
 #include <grpc/support/slice_buffer.h>
 
 /* compress 'input' to 'output' using 'algorithm'.
diff --git a/src/core/surface/byte_buffer.c b/src/core/surface/byte_buffer.c
index 12244f6644..4817e00454 100644
--- a/src/core/surface/byte_buffer.c
+++ b/src/core/surface/byte_buffer.c
@@ -35,25 +35,31 @@
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 
-grpc_byte_buffer *grpc_byte_buffer_create(gpr_slice *slices, size_t nslices) {
+grpc_byte_buffer *grpc_raw_byte_buffer_create(gpr_slice *slices,
+                                              size_t nslices) {
+  return grpc_raw_compressed_byte_buffer_create(slices, nslices,
+                                                GRPC_COMPRESS_NONE);
+}
+
+grpc_byte_buffer *grpc_raw_compressed_byte_buffer_create(
+    gpr_slice *slices, size_t nslices, grpc_compression_algorithm compression) {
   size_t i;
   grpc_byte_buffer *bb = malloc(sizeof(grpc_byte_buffer));
-
-  bb->type = GRPC_BB_SLICE_BUFFER;
-  gpr_slice_buffer_init(&bb->data.slice_buffer);
+  bb->type = GRPC_BB_RAW;
+  bb->data.raw.compression = compression;
+  gpr_slice_buffer_init(&bb->data.raw.slice_buffer);
   for (i = 0; i < nslices; i++) {
     gpr_slice_ref(slices[i]);
-    gpr_slice_buffer_add(&bb->data.slice_buffer, slices[i]);
+    gpr_slice_buffer_add(&bb->data.raw.slice_buffer, slices[i]);
   }
-
   return bb;
 }
 
 grpc_byte_buffer *grpc_byte_buffer_copy(grpc_byte_buffer *bb) {
   switch (bb->type) {
-    case GRPC_BB_SLICE_BUFFER:
-      return grpc_byte_buffer_create(bb->data.slice_buffer.slices,
-                                     bb->data.slice_buffer.count);
+    case GRPC_BB_RAW:
+      return grpc_raw_byte_buffer_create(bb->data.raw.slice_buffer.slices,
+                                         bb->data.raw.slice_buffer.count);
   }
   gpr_log(GPR_INFO, "should never get here");
   abort();
@@ -63,8 +69,8 @@ grpc_byte_buffer *grpc_byte_buffer_copy(grpc_byte_buffer *bb) {
 void grpc_byte_buffer_destroy(grpc_byte_buffer *bb) {
   if (!bb) return;
   switch (bb->type) {
-    case GRPC_BB_SLICE_BUFFER:
-      gpr_slice_buffer_destroy(&bb->data.slice_buffer);
+    case GRPC_BB_RAW:
+      gpr_slice_buffer_destroy(&bb->data.raw.slice_buffer);
       break;
   }
   free(bb);
@@ -72,8 +78,8 @@ void grpc_byte_buffer_destroy(grpc_byte_buffer *bb) {
 
 size_t grpc_byte_buffer_length(grpc_byte_buffer *bb) {
   switch (bb->type) {
-    case GRPC_BB_SLICE_BUFFER:
-      return bb->data.slice_buffer.length;
+    case GRPC_BB_RAW:
+      return bb->data.raw.slice_buffer.length;
   }
   gpr_log(GPR_ERROR, "should never reach here");
   abort();
diff --git a/src/core/surface/byte_buffer_reader.c b/src/core/surface/byte_buffer_reader.c
index 41ad700274..86829a686f 100644
--- a/src/core/surface/byte_buffer_reader.c
+++ b/src/core/surface/byte_buffer_reader.c
@@ -33,41 +33,73 @@
 
 #include <grpc/byte_buffer_reader.h>
 
+#include <grpc/compression.h>
 #include <grpc/grpc.h>
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 #include <grpc/support/slice_buffer.h>
 #include <grpc/byte_buffer.h>
 
+#include "src/core/compression/message_compress.h"
+
+static int is_compressed(grpc_byte_buffer *buffer) {
+  switch (buffer->type) {
+    case GRPC_BB_RAW:
+      if (buffer->data.raw.compression == GRPC_COMPRESS_NONE) {
+        return 0 /* GPR_FALSE */;
+      }
+      break;
+  }
+  return 1 /* GPR_TRUE */;
+}
+
 void grpc_byte_buffer_reader_init(grpc_byte_buffer_reader *reader,
                                   grpc_byte_buffer *buffer) {
-  reader->buffer = buffer;
-  switch (buffer->type) {
-    case GRPC_BB_SLICE_BUFFER:
+  gpr_slice_buffer decompressed_slices_buffer;
+  reader->buffer_in = buffer;
+  switch (reader->buffer_in->type) {
+    case GRPC_BB_RAW:
+      gpr_slice_buffer_init(&decompressed_slices_buffer);
+      if (is_compressed(reader->buffer_in)) {
+        grpc_msg_decompress(reader->buffer_in->data.raw.compression,
+                            &reader->buffer_in->data.raw.slice_buffer,
+                            &decompressed_slices_buffer);
+        reader->buffer_out = grpc_raw_byte_buffer_create(
+            decompressed_slices_buffer.slices,
+            decompressed_slices_buffer.count);
+        gpr_slice_buffer_destroy(&decompressed_slices_buffer);
+      } else {  /* not compressed, use the input buffer as output */
+        reader->buffer_out = reader->buffer_in;
+      }
       reader->current.index = 0;
+      break;
   }
 }
 
 void grpc_byte_buffer_reader_destroy(grpc_byte_buffer_reader *reader) {
-  /* no-op: the user is responsible for memory deallocation.
-   * Other cleanup operations would go here if needed. */
+  switch (reader->buffer_in->type) {
+    case GRPC_BB_RAW:
+      /* keeping the same if-else structure as in the init function */
+      if (is_compressed(reader->buffer_in)) {
+        grpc_byte_buffer_destroy(reader->buffer_out);
+      }
+      break;
+  }
 }
 
 int grpc_byte_buffer_reader_next(grpc_byte_buffer_reader *reader,
                                  gpr_slice *slice) {
-  grpc_byte_buffer *buffer = reader->buffer;
-  gpr_slice_buffer *slice_buffer;
-  switch (buffer->type) {
-    case GRPC_BB_SLICE_BUFFER:
-      slice_buffer = &buffer->data.slice_buffer;
+  switch (reader->buffer_in->type) {
+    case GRPC_BB_RAW: {
+      gpr_slice_buffer *slice_buffer;
+      slice_buffer = &reader->buffer_out->data.raw.slice_buffer;
       if (reader->current.index < slice_buffer->count) {
         *slice = gpr_slice_ref(slice_buffer->slices[reader->current.index]);
         reader->current.index += 1;
         return 1;
-      } else {
-        return 0;
       }
       break;
+    }
   }
   return 0;
 }
diff --git a/src/core/surface/call.c b/src/core/surface/call.c
index 74df5745b5..cead5e08dc 100644
--- a/src/core/surface/call.c
+++ b/src/core/surface/call.c
@@ -636,7 +636,7 @@ static void call_on_done_send(void *pc, int success) {
 
 static void finish_message(grpc_call *call) {
   /* TODO(ctiller): this could be a lot faster if coded directly */
-  grpc_byte_buffer *byte_buffer = grpc_byte_buffer_create(
+  grpc_byte_buffer *byte_buffer = grpc_raw_byte_buffer_create(
       call->incoming_message.slices, call->incoming_message.count);
   gpr_slice_buffer_reset_and_unref(&call->incoming_message);
 
@@ -759,7 +759,7 @@ static void call_on_done_recv(void *pc, int success) {
   unlock(call);
 
   GRPC_CALL_INTERNAL_UNREF(call, "receiving", 0);
-  GRPC_TIMER_BEGIN(GRPC_PTAG_CALL_ON_DONE_RECV, 0);
+  GRPC_TIMER_END(GRPC_PTAG_CALL_ON_DONE_RECV, 0);
 }
 
 static int prepare_application_metadata(grpc_call *call, size_t count,
@@ -806,9 +806,9 @@ static void copy_byte_buffer_to_stream_ops(grpc_byte_buffer *byte_buffer,
   size_t i;
 
   switch (byte_buffer->type) {
-    case GRPC_BB_SLICE_BUFFER:
-      for (i = 0; i < byte_buffer->data.slice_buffer.count; i++) {
-        gpr_slice slice = byte_buffer->data.slice_buffer.slices[i];
+    case GRPC_BB_RAW:
+      for (i = 0; i < byte_buffer->data.raw.slice_buffer.count; i++) {
+        gpr_slice slice = byte_buffer->data.raw.slice_buffer.slices[i];
         gpr_slice_ref(slice);
         grpc_sopb_add_slice(sopb, slice);
       }
@@ -820,7 +820,6 @@ static int fill_send_ops(grpc_call *call, grpc_transport_op *op) {
   grpc_ioreq_data data;
   grpc_metadata_batch mdb;
   size_t i;
-  char status_str[GPR_LTOA_MIN_BUFSIZE];
   GPR_ASSERT(op->send_ops == NULL);
 
   switch (call->write_state) {
@@ -865,13 +864,10 @@ static int fill_send_ops(grpc_call *call, grpc_transport_op *op) {
           /* send status */
           /* TODO(ctiller): cache common status values */
           data = call->request_data[GRPC_IOREQ_SEND_STATUS];
-          gpr_ltoa(data.send_status.code, status_str);
           grpc_metadata_batch_add_tail(
               &mdb, &call->status_link,
-              grpc_mdelem_from_metadata_strings(
-                  call->metadata_context,
-                  grpc_mdstr_ref(grpc_channel_get_status_string(call->channel)),
-                  grpc_mdstr_from_string(call->metadata_context, status_str)));
+              grpc_channel_get_reffed_status_elem(call->channel,
+                                                  data.send_status.code));
           if (data.send_status.details) {
             grpc_metadata_batch_add_tail(
                 &mdb, &call->details_link,
diff --git a/src/core/surface/channel.c b/src/core/surface/channel.c
index 947011c613..9175ad0572 100644
--- a/src/core/surface/channel.c
+++ b/src/core/surface/channel.c
@@ -37,12 +37,20 @@
 #include <string.h>
 
 #include "src/core/iomgr/iomgr.h"
+#include "src/core/support/string.h"
 #include "src/core/surface/call.h"
 #include "src/core/surface/client.h"
 #include "src/core/surface/init.h"
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 
+/** Cache grpc-status: X mdelems for X = 0..NUM_CACHED_STATUS_ELEMS.
+ *  Avoids needing to take a metadata context lock for sending status
+ *  if the status code is <= NUM_CACHED_STATUS_ELEMS.
+ *  Sized to allow the most commonly used codes to fit in
+ *  (OK, Cancelled, Unknown). */
+#define NUM_CACHED_STATUS_ELEMS 3
+
 typedef struct registered_call {
   grpc_mdelem *path;
   grpc_mdelem *authority;
@@ -54,10 +62,13 @@ struct grpc_channel {
   gpr_refcount refs;
   gpr_uint32 max_message_length;
   grpc_mdctx *metadata_context;
+  /** mdstr for the grpc-status key */
   grpc_mdstr *grpc_status_string;
   grpc_mdstr *grpc_message_string;
   grpc_mdstr *path_string;
   grpc_mdstr *authority_string;
+  /** mdelem for grpc-status: 0 thru grpc-status: 2 */
+  grpc_mdelem *grpc_status_elem[NUM_CACHED_STATUS_ELEMS];
 
   gpr_mu registered_call_mu;
   registered_call *registered_calls;
@@ -88,6 +99,13 @@ grpc_channel *grpc_channel_create_from_filters(
   channel->metadata_context = mdctx;
   channel->grpc_status_string = grpc_mdstr_from_string(mdctx, "grpc-status");
   channel->grpc_message_string = grpc_mdstr_from_string(mdctx, "grpc-message");
+  for (i = 0; i < NUM_CACHED_STATUS_ELEMS; i++) {
+    char buf[GPR_LTOA_MIN_BUFSIZE];
+    gpr_ltoa(i, buf);
+    channel->grpc_status_elem[i] = grpc_mdelem_from_metadata_strings(
+        mdctx, grpc_mdstr_ref(channel->grpc_status_string),
+        grpc_mdstr_from_string(mdctx, buf));
+  }
   channel->path_string = grpc_mdstr_from_string(mdctx, ":path");
   channel->authority_string = grpc_mdstr_from_string(mdctx, ":authority");
   grpc_channel_stack_init(filters, num_filters, args, channel->metadata_context,
@@ -175,7 +193,11 @@ void grpc_channel_internal_ref(grpc_channel *channel) {
 
 static void destroy_channel(void *p, int ok) {
   grpc_channel *channel = p;
+  size_t i;
   grpc_channel_stack_destroy(CHANNEL_STACK_FROM_CHANNEL(channel));
+  for (i = 0; i < NUM_CACHED_STATUS_ELEMS; i++) {
+    grpc_mdelem_unref(channel->grpc_status_elem[i]);
+  }
   grpc_mdstr_unref(channel->grpc_status_string);
   grpc_mdstr_unref(channel->grpc_message_string);
   grpc_mdstr_unref(channel->path_string);
@@ -235,6 +257,18 @@ grpc_mdstr *grpc_channel_get_status_string(grpc_channel *channel) {
   return channel->grpc_status_string;
 }
 
+grpc_mdelem *grpc_channel_get_reffed_status_elem(grpc_channel *channel, int i) {
+  if (i >= 0 && i < NUM_CACHED_STATUS_ELEMS) {
+    return grpc_mdelem_ref(channel->grpc_status_elem[i]);
+  } else {
+    char tmp[GPR_LTOA_MIN_BUFSIZE];
+    gpr_ltoa(i, tmp);
+    return grpc_mdelem_from_metadata_strings(
+        channel->metadata_context, grpc_mdstr_ref(channel->grpc_status_string),
+        grpc_mdstr_from_string(channel->metadata_context, tmp));
+  }
+}
+
 grpc_mdstr *grpc_channel_get_message_string(grpc_channel *channel) {
   return channel->grpc_message_string;
 }
diff --git a/src/core/surface/channel.h b/src/core/surface/channel.h
index 388be35711..6d1ed87900 100644
--- a/src/core/surface/channel.h
+++ b/src/core/surface/channel.h
@@ -40,8 +40,18 @@ grpc_channel *grpc_channel_create_from_filters(
     const grpc_channel_filter **filters, size_t count,
     const grpc_channel_args *args, grpc_mdctx *mdctx, int is_client);
 
+/** Get a (borrowed) pointer to this channels underlying channel stack */
 grpc_channel_stack *grpc_channel_get_channel_stack(grpc_channel *channel);
+
+/** Get a (borrowed) pointer to the channel wide metadata context */
 grpc_mdctx *grpc_channel_get_metadata_context(grpc_channel *channel);
+
+/** Get a grpc_mdelem of grpc-status: X where X is the numeric value of
+    status_code.
+
+    The returned elem is owned by the caller. */
+grpc_mdelem *grpc_channel_get_reffed_status_elem(grpc_channel *channel,
+                                                 int status_code);
 grpc_mdstr *grpc_channel_get_status_string(grpc_channel *channel);
 grpc_mdstr *grpc_channel_get_message_string(grpc_channel *channel);
 gpr_uint32 grpc_channel_get_max_message_length(grpc_channel *channel);
diff --git a/src/core/transport/chttp2_transport.c b/src/core/transport/chttp2_transport.c
index 630504565b..bd259f7ae3 100644
--- a/src/core/transport/chttp2_transport.c
+++ b/src/core/transport/chttp2_transport.c
@@ -230,7 +230,10 @@ struct transport {
   /* basic state management - what are we doing at the moment? */
   gpr_uint8 reading;
   gpr_uint8 writing;
-  gpr_uint8 calling_back;
+  /** are we calling back (via cb) with a channel-level event */
+  gpr_uint8 calling_back_channel;
+  /** are we calling back any grpc_transport_op completion events */
+  gpr_uint8 calling_back_ops;
   gpr_uint8 destroying;
   gpr_uint8 closed;
   error_state error_state;
@@ -357,7 +360,7 @@ static void push_setting(transport *t, grpc_chttp2_setting_id id,
                          gpr_uint32 value);
 
 static int prepare_callbacks(transport *t);
-static void run_callbacks(transport *t, const grpc_transport_callbacks *cb);
+static void run_callbacks(transport *t);
 static void call_cb_closed(transport *t, const grpc_transport_callbacks *cb);
 
 static int prepare_write(transport *t);
@@ -565,7 +568,7 @@ static void init_transport(transport *t, grpc_transport_setup_callback setup,
   }
 
   gpr_mu_lock(&t->mu);
-  t->calling_back = 1;
+  t->calling_back_channel = 1;
   ref_transport(t); /* matches unref at end of this function */
   gpr_mu_unlock(&t->mu);
 
@@ -574,7 +577,7 @@ static void init_transport(transport *t, grpc_transport_setup_callback setup,
   lock(t);
   t->cb = sr.callbacks;
   t->cb_user_data = sr.user_data;
-  t->calling_back = 0;
+  t->calling_back_channel = 0;
   if (t->destroying) gpr_cv_signal(&t->cv);
   unlock(t);
 
@@ -595,7 +598,7 @@ static void destroy_transport(grpc_transport *gt) {
      We need to be not writing as cancellation finalization may produce some
      callbacks that NEED to be made to close out some streams when t->writing
      becomes 0. */
-  while (t->calling_back || t->writing) {
+  while (t->calling_back_channel || t->writing) {
     gpr_cv_wait(&t->cv, &t->mu, gpr_inf_future);
   }
   drop_connection(t);
@@ -830,28 +833,29 @@ static void unlock(transport *t) {
   finish_reads(t);
 
   /* gather any callbacks that need to be made */
-  if (!t->calling_back) {
-    t->calling_back = perform_callbacks = prepare_callbacks(t);
-    if (cb) {
-      if (t->error_state == ERROR_STATE_SEEN && !t->writing) {
-        call_closed = 1;
-        t->calling_back = 1;
-        t->cb = NULL; /* no more callbacks */
-        t->error_state = ERROR_STATE_NOTIFIED;
-      }
-      if (t->num_pending_goaways) {
-        goaways = t->pending_goaways;
-        num_goaways = t->num_pending_goaways;
-        t->pending_goaways = NULL;
-        t->num_pending_goaways = 0;
-        t->cap_pending_goaways = 0;
-        t->calling_back = 1;
-      }
-    }
+  if (!t->calling_back_ops) {
+    t->calling_back_ops = perform_callbacks = prepare_callbacks(t);
+    if (perform_callbacks) ref_transport(t);
   }
 
-  if (perform_callbacks || call_closed || num_goaways) {
-    ref_transport(t);
+  if (!t->calling_back_channel && cb) {
+    if (t->error_state == ERROR_STATE_SEEN && !t->writing) {
+      call_closed = 1;
+      t->calling_back_channel = 1;
+      t->cb = NULL; /* no more callbacks */
+      t->error_state = ERROR_STATE_NOTIFIED;
+    }
+    if (t->num_pending_goaways) {
+      goaways = t->pending_goaways;
+      num_goaways = t->num_pending_goaways;
+      t->pending_goaways = NULL;
+      t->num_pending_goaways = 0;
+      t->cap_pending_goaways = 0;
+      t->calling_back_channel = 1;
+    }
+    if (call_closed || num_goaways) {
+      ref_transport(t);
+    }
   }
 
   /* finally unlock */
@@ -865,7 +869,11 @@ static void unlock(transport *t) {
   }
 
   if (perform_callbacks) {
-    run_callbacks(t, cb);
+    run_callbacks(t);
+    lock(t);
+    t->calling_back_ops = 0;
+    unlock(t);
+    unref_transport(t);
   }
 
   if (call_closed) {
@@ -878,9 +886,9 @@ static void unlock(transport *t) {
     perform_write(t, ep);
   }
 
-  if (perform_callbacks || call_closed || num_goaways) {
+  if (call_closed || num_goaways) {
     lock(t);
-    t->calling_back = 0;
+    t->calling_back_channel = 0;
     if (t->destroying) gpr_cv_signal(&t->cv);
     unlock(t);
     unref_transport(t);
@@ -2101,7 +2109,7 @@ static int prepare_callbacks(transport *t) {
   return t->executing_callbacks.count > 0;
 }
 
-static void run_callbacks(transport *t, const grpc_transport_callbacks *cb) {
+static void run_callbacks(transport *t) {
   size_t i;
   for (i = 0; i < t->executing_callbacks.count; i++) {
     op_closure c = t->executing_callbacks.callbacks[i];
diff --git a/src/core/transport/metadata.c b/src/core/transport/metadata.c
index c80d67823f..e75b449e12 100644
--- a/src/core/transport/metadata.c
+++ b/src/core/transport/metadata.c
@@ -120,7 +120,7 @@ static void unlock(grpc_mdctx *ctx) {
   if (ctx->refs == 0) {
     /* uncomment if you're having trouble diagnosing an mdelem leak to make
        things clearer (slows down destruction a lot, however) */
-    gc_mdtab(ctx);
+    /* gc_mdtab(ctx); */
     if (ctx->mdtab_count && ctx->mdtab_count == ctx->mdtab_free) {
       discard_metadata(ctx);
     }