Introduce grpc_byte_buffer_reader_peek and use it for Protobuf parsing.

grpc_byte_buffer_reader_next() copies and references the slice. This
is not always necessary since the caller will not use the slice
after destroying the byte buffer.

A prominent example is the protobuf parser, which
calls grpc_byte_buffer_reader_next() and immediately unrefs the slice
after the call. This ref() and unref() calls can be very expensive
in the hot path.

This commit introduces grpc_byte_buffer_reader_peek() which
essentialy return a pointer to the slice in the buffer, i.e.,
no copies, and no refs.

QPS of 1MiB 1 Channel callback benchmark increases by 5%.
More importantly insructions per cycle is increased by 10%.

Also add tests and benchmarks for byte_buffer_reader_peek()

grpc.def

@@ -149,6 +149,7 @@ EXPORTS
     grpc_byte_buffer_reader_init
     grpc_byte_buffer_reader_destroy
     grpc_byte_buffer_reader_next
+    grpc_byte_buffer_reader_peek
     grpc_byte_buffer_reader_readall
     grpc_raw_byte_buffer_from_reader
     gpr_log_severity_string

include/grpc/impl/codegen/byte_buffer.h

@@ -73,6 +73,19 @@ GRPCAPI void grpc_byte_buffer_reader_destroy(grpc_byte_buffer_reader* reader);
 GRPCAPI int grpc_byte_buffer_reader_next(grpc_byte_buffer_reader* reader,
                                          grpc_slice* slice);
 
+/** EXPERIMENTAL API - This function may be removed and changed, in the future.
+ *
+ * Updates \a slice with the next piece of data from from \a reader and returns
+ * 1. Returns 0 at the end of the stream. Caller is responsible for making sure
+ * the slice pointer remains valid when accessed.
+ *
+ * NOTE: Do not use this function unless the caller can guarantee that the
+ *       underlying grpc_byte_buffer outlasts the use of the slice. This is only
+ *       safe when the underlying grpc_byte_buffer remains immutable while slice
+ *       is being accessed. */
+GRPCAPI int grpc_byte_buffer_reader_peek(grpc_byte_buffer_reader* reader,
+                                         grpc_slice** slice);
+
 /** Merge all data from \a reader into single slice */
 GRPCAPI grpc_slice
 grpc_byte_buffer_reader_readall(grpc_byte_buffer_reader* reader);

include/grpcpp/impl/codegen/core_codegen.h

@@ -85,6 +85,8 @@ class CoreCodegen final : public CoreCodegenInterface {
       grpc_byte_buffer_reader* reader) override;
   int grpc_byte_buffer_reader_next(grpc_byte_buffer_reader* reader,
                                    grpc_slice* slice) override;
+  int grpc_byte_buffer_reader_peek(grpc_byte_buffer_reader* reader,
+                                   grpc_slice** slice) override;
 
   grpc_byte_buffer* grpc_raw_byte_buffer_create(grpc_slice* slice,
                                                 size_t nslices) override;

include/grpcpp/impl/codegen/core_codegen_interface.h

@@ -92,6 +92,8 @@ class CoreCodegenInterface {
       grpc_byte_buffer_reader* reader) = 0;
   virtual int grpc_byte_buffer_reader_next(grpc_byte_buffer_reader* reader,
                                            grpc_slice* slice) = 0;
+  virtual int grpc_byte_buffer_reader_peek(grpc_byte_buffer_reader* reader,
+                                           grpc_slice** slice) = 0;
 
   virtual grpc_byte_buffer* grpc_raw_byte_buffer_create(grpc_slice* slice,
                                                         size_t nslices) = 0;

include/grpcpp/impl/codegen/proto_buffer_reader.h

@@ -73,7 +73,7 @@ class ProtoBufferReader : public ::grpc::protobuf::io::ZeroCopyInputStream {
     }
     /// If we have backed up previously, we need to return the backed-up slice
     if (backup_count_ > 0) {
-      *data = GRPC_SLICE_START_PTR(slice_) + GRPC_SLICE_LENGTH(slice_) -
+      *data = GRPC_SLICE_START_PTR(*slice_) + GRPC_SLICE_LENGTH(*slice_) -
               backup_count_;
       GPR_CODEGEN_ASSERT(backup_count_ <= INT_MAX);
       *size = (int)backup_count_;
@@ -81,15 +81,14 @@ class ProtoBufferReader : public ::grpc::protobuf::io::ZeroCopyInputStream {
       return true;
     }
     /// Otherwise get the next slice from the byte buffer reader
-    if (!g_core_codegen_interface->grpc_byte_buffer_reader_next(&reader_,
+    if (!g_core_codegen_interface->grpc_byte_buffer_reader_peek(&reader_,
                                                                 &slice_)) {
       return false;
     }
-    g_core_codegen_interface->grpc_slice_unref(slice_);
-    *data = GRPC_SLICE_START_PTR(slice_);
+    *data = GRPC_SLICE_START_PTR(*slice_);
     // On win x64, int is only 32bit
-    GPR_CODEGEN_ASSERT(GRPC_SLICE_LENGTH(slice_) <= INT_MAX);
-    byte_count_ += * size = (int)GRPC_SLICE_LENGTH(slice_);
+    GPR_CODEGEN_ASSERT(GRPC_SLICE_LENGTH(*slice_) <= INT_MAX);
+    byte_count_ += * size = (int)GRPC_SLICE_LENGTH(*slice_);
     return true;
   }
 
@@ -100,7 +99,7 @@ class ProtoBufferReader : public ::grpc::protobuf::io::ZeroCopyInputStream {
   /// bytes that have already been returned by the last call of Next.
   /// So do the backup and have that ready for a later Next.
   void BackUp(int count) override {
-    GPR_CODEGEN_ASSERT(count <= static_cast<int>(GRPC_SLICE_LENGTH(slice_)));
+    GPR_CODEGEN_ASSERT(count <= static_cast<int>(GRPC_SLICE_LENGTH(*slice_)));
     backup_count_ = count;
   }
 
@@ -135,14 +134,15 @@ class ProtoBufferReader : public ::grpc::protobuf::io::ZeroCopyInputStream {
   int64_t backup_count() { return backup_count_; }
   void set_backup_count(int64_t backup_count) { backup_count_ = backup_count; }
   grpc_byte_buffer_reader* reader() { return &reader_; }
-  grpc_slice* slice() { return &slice_; }
+  grpc_slice* slice() { return slice_; }
+  grpc_slice** mutable_slice_ptr() { return &slice_; }
 
  private:
   int64_t byte_count_;              ///< total bytes read since object creation
   int64_t backup_count_;            ///< how far backed up in the stream we are
   grpc_byte_buffer_reader reader_;  ///< internal object to read \a grpc_slice
                                     ///< from the \a grpc_byte_buffer
-  grpc_slice slice_;                ///< current slice passed back to the caller
+  grpc_slice* slice_;               ///< current slice passed back to the caller
   Status status_;                   ///< status of the entire object
 };
 

src/core/lib/surface/byte_buffer_reader.cc

@@ -91,6 +91,23 @@ void grpc_byte_buffer_reader_destroy(grpc_byte_buffer_reader* reader) {
   }
 }
 
+int grpc_byte_buffer_reader_peek(grpc_byte_buffer_reader* reader,
+                                 grpc_slice** slice) {
+  switch (reader->buffer_in->type) {
+    case GRPC_BB_RAW: {
+      grpc_slice_buffer* slice_buffer;
+      slice_buffer = &reader->buffer_out->data.raw.slice_buffer;
+      if (reader->current.index < slice_buffer->count) {
+        *slice = &slice_buffer->slices[reader->current.index];
+        reader->current.index += 1;
+        return 1;
+      }
+      break;
+    }
+  }
+  return 0;
+}
+
 int grpc_byte_buffer_reader_next(grpc_byte_buffer_reader* reader,
                                  grpc_slice* slice) {
   switch (reader->buffer_in->type) {

src/cpp/common/core_codegen.cc

@@ -139,6 +139,11 @@ int CoreCodegen::grpc_byte_buffer_reader_next(grpc_byte_buffer_reader* reader,
   return ::grpc_byte_buffer_reader_next(reader, slice);
 }
 
+int CoreCodegen::grpc_byte_buffer_reader_peek(grpc_byte_buffer_reader* reader,
+                                              grpc_slice** slice) {
+  return ::grpc_byte_buffer_reader_peek(reader, slice);
+}
+
 grpc_byte_buffer* CoreCodegen::grpc_raw_byte_buffer_create(grpc_slice* slice,
                                                            size_t nslices) {
   return ::grpc_raw_byte_buffer_create(slice, nslices);

src/ruby/ext/grpc/rb_grpc_imports.generated.c

@@ -172,6 +172,7 @@ grpc_byte_buffer_destroy_type grpc_byte_buffer_destroy_import;
 grpc_byte_buffer_reader_init_type grpc_byte_buffer_reader_init_import;
 grpc_byte_buffer_reader_destroy_type grpc_byte_buffer_reader_destroy_import;
 grpc_byte_buffer_reader_next_type grpc_byte_buffer_reader_next_import;
+grpc_byte_buffer_reader_peek_type grpc_byte_buffer_reader_peek_import;
 grpc_byte_buffer_reader_readall_type grpc_byte_buffer_reader_readall_import;
 grpc_raw_byte_buffer_from_reader_type grpc_raw_byte_buffer_from_reader_import;
 gpr_log_severity_string_type gpr_log_severity_string_import;
@@ -440,6 +441,7 @@ void grpc_rb_load_imports(HMODULE library) {
   grpc_byte_buffer_reader_init_import = (grpc_byte_buffer_reader_init_type) GetProcAddress(library, "grpc_byte_buffer_reader_init");
   grpc_byte_buffer_reader_destroy_import = (grpc_byte_buffer_reader_destroy_type) GetProcAddress(library, "grpc_byte_buffer_reader_destroy");
   grpc_byte_buffer_reader_next_import = (grpc_byte_buffer_reader_next_type) GetProcAddress(library, "grpc_byte_buffer_reader_next");
+  grpc_byte_buffer_reader_peek_import = (grpc_byte_buffer_reader_peek_type) GetProcAddress(library, "grpc_byte_buffer_reader_peek");
   grpc_byte_buffer_reader_readall_import = (grpc_byte_buffer_reader_readall_type) GetProcAddress(library, "grpc_byte_buffer_reader_readall");
   grpc_raw_byte_buffer_from_reader_import = (grpc_raw_byte_buffer_from_reader_type) GetProcAddress(library, "grpc_raw_byte_buffer_from_reader");
   gpr_log_severity_string_import = (gpr_log_severity_string_type) GetProcAddress(library, "gpr_log_severity_string");

src/ruby/ext/grpc/rb_grpc_imports.generated.h

@@ -491,6 +491,9 @@ extern grpc_byte_buffer_reader_destroy_type grpc_byte_buffer_reader_destroy_impo
 typedef int(*grpc_byte_buffer_reader_next_type)(grpc_byte_buffer_reader* reader, grpc_slice* slice);
 extern grpc_byte_buffer_reader_next_type grpc_byte_buffer_reader_next_import;
 #define grpc_byte_buffer_reader_next grpc_byte_buffer_reader_next_import
+typedef int(*grpc_byte_buffer_reader_peek_type)(grpc_byte_buffer_reader* reader, grpc_slice** slice);
+extern grpc_byte_buffer_reader_peek_type grpc_byte_buffer_reader_peek_import;
+#define grpc_byte_buffer_reader_peek grpc_byte_buffer_reader_peek_import
 typedef grpc_slice(*grpc_byte_buffer_reader_readall_type)(grpc_byte_buffer_reader* reader);
 extern grpc_byte_buffer_reader_readall_type grpc_byte_buffer_reader_readall_import;
 #define grpc_byte_buffer_reader_readall grpc_byte_buffer_reader_readall_import

test/core/surface/byte_buffer_reader_test.cc

@@ -101,6 +101,73 @@ static void test_read_none_compressed_slice(void) {
   grpc_byte_buffer_destroy(buffer);
 }
 
+static void test_peek_one_slice(void) {
+  grpc_slice slice;
+  grpc_byte_buffer* buffer;
+  grpc_byte_buffer_reader reader;
+  grpc_slice* first_slice;
+  grpc_slice* second_slice;
+  int first_code, second_code;
+
+  LOG_TEST("test_peek_one_slice");
+  slice = grpc_slice_from_copied_string("test");
+  buffer = grpc_raw_byte_buffer_create(&slice, 1);
+  grpc_slice_unref(slice);
+  GPR_ASSERT(grpc_byte_buffer_reader_init(&reader, buffer) &&
+             "Couldn't init byte buffer reader");
+  first_code = grpc_byte_buffer_reader_peek(&reader, &first_slice);
+  GPR_ASSERT(first_code != 0);
+  GPR_ASSERT(memcmp(GRPC_SLICE_START_PTR(*first_slice), "test", 4) == 0);
+  second_code = grpc_byte_buffer_reader_peek(&reader, &second_slice);
+  GPR_ASSERT(second_code == 0);
+  grpc_byte_buffer_destroy(buffer);
+}
+
+static void test_peek_one_slice_malloc(void) {
+  grpc_slice slice;
+  grpc_byte_buffer* buffer;
+  grpc_byte_buffer_reader reader;
+  grpc_slice* first_slice;
+  grpc_slice* second_slice;
+  int first_code, second_code;
+
+  LOG_TEST("test_peek_one_slice_malloc");
+  slice = grpc_slice_malloc(4);
+  memcpy(GRPC_SLICE_START_PTR(slice), "test", 4);
+  buffer = grpc_raw_byte_buffer_create(&slice, 1);
+  grpc_slice_unref(slice);
+  GPR_ASSERT(grpc_byte_buffer_reader_init(&reader, buffer) &&
+             "Couldn't init byte buffer reader");
+  first_code = grpc_byte_buffer_reader_peek(&reader, &first_slice);
+  GPR_ASSERT(first_code != 0);
+  GPR_ASSERT(memcmp(GRPC_SLICE_START_PTR(*first_slice), "test", 4) == 0);
+  second_code = grpc_byte_buffer_reader_peek(&reader, &second_slice);
+  GPR_ASSERT(second_code == 0);
+  grpc_byte_buffer_destroy(buffer);
+}
+
+static void test_peek_none_compressed_slice(void) {
+  grpc_slice slice;
+  grpc_byte_buffer* buffer;
+  grpc_byte_buffer_reader reader;
+  grpc_slice* first_slice;
+  grpc_slice* second_slice;
+  int first_code, second_code;
+
+  LOG_TEST("test_peek_none_compressed_slice");
+  slice = grpc_slice_from_copied_string("test");
+  buffer = grpc_raw_byte_buffer_create(&slice, 1);
+  grpc_slice_unref(slice);
+  GPR_ASSERT(grpc_byte_buffer_reader_init(&reader, buffer) &&
+             "Couldn't init byte buffer reader");
+  first_code = grpc_byte_buffer_reader_peek(&reader, &first_slice);
+  GPR_ASSERT(first_code != 0);
+  GPR_ASSERT(memcmp(GRPC_SLICE_START_PTR(*first_slice), "test", 4) == 0);
+  second_code = grpc_byte_buffer_reader_peek(&reader, &second_slice);
+  GPR_ASSERT(second_code == 0);
+  grpc_byte_buffer_destroy(buffer);
+}
+
 static void test_read_corrupted_slice(void) {
   grpc_slice slice;
   grpc_byte_buffer* buffer;
@@ -271,6 +338,9 @@ int main(int argc, char** argv) {
   test_read_one_slice();
   test_read_one_slice_malloc();
   test_read_none_compressed_slice();
+  test_peek_one_slice();
+  test_peek_one_slice_malloc();
+  test_peek_none_compressed_slice();
   test_read_gzip_compressed_slice();
   test_read_deflate_compressed_slice();
   test_read_corrupted_slice();

test/core/surface/public_headers_must_be_c89.c

@@ -209,6 +209,7 @@ int main(int argc, char **argv) {
   printf("%lx", (unsigned long) grpc_byte_buffer_reader_init);
   printf("%lx", (unsigned long) grpc_byte_buffer_reader_destroy);
   printf("%lx", (unsigned long) grpc_byte_buffer_reader_next);
+  printf("%lx", (unsigned long) grpc_byte_buffer_reader_peek);
   printf("%lx", (unsigned long) grpc_byte_buffer_reader_readall);
   printf("%lx", (unsigned long) grpc_raw_byte_buffer_from_reader);
   printf("%lx", (unsigned long) gpr_log_severity_string);

test/cpp/microbenchmarks/bm_byte_buffer.cc

@@ -29,9 +29,8 @@
 namespace grpc {
 namespace testing {
 
-auto& force_library_initialization = Library::get();
-
 static void BM_ByteBuffer_Copy(benchmark::State& state) {
+  Library::get();
   int num_slices = state.range(0);
   size_t slice_size = state.range(1);
   std::vector<grpc::Slice> slices;
@@ -48,6 +47,74 @@ static void BM_ByteBuffer_Copy(benchmark::State& state) {
 }
 BENCHMARK(BM_ByteBuffer_Copy)->Ranges({{1, 64}, {1, 1024 * 1024}});
 
+static void BM_ByteBufferReader_Next(benchmark::State& state) {
+  Library::get();
+  const int num_slices = state.range(0);
+  constexpr size_t kSliceSize = 16;
+  std::vector<grpc_slice> slices;
+  for (int i = 0; i < num_slices; ++i) {
+    std::unique_ptr<char[]> buf(new char[kSliceSize]);
+    slices.emplace_back(g_core_codegen_interface->grpc_slice_from_copied_buffer(
+        buf.get(), kSliceSize));
+  }
+  grpc_byte_buffer* bb = g_core_codegen_interface->grpc_raw_byte_buffer_create(
+      slices.data(), num_slices);
+  grpc_byte_buffer_reader reader;
+  GPR_ASSERT(
+      g_core_codegen_interface->grpc_byte_buffer_reader_init(&reader, bb));
+  while (state.KeepRunning()) {
+    grpc_slice* slice;
+    if (GPR_UNLIKELY(!g_core_codegen_interface->grpc_byte_buffer_reader_peek(
+            &reader, &slice))) {
+      g_core_codegen_interface->grpc_byte_buffer_reader_destroy(&reader);
+      GPR_ASSERT(
+          g_core_codegen_interface->grpc_byte_buffer_reader_init(&reader, bb));
+      continue;
+    }
+  }
+
+  g_core_codegen_interface->grpc_byte_buffer_reader_destroy(&reader);
+  g_core_codegen_interface->grpc_byte_buffer_destroy(bb);
+  for (auto& slice : slices) {
+    g_core_codegen_interface->grpc_slice_unref(slice);
+  }
+}
+BENCHMARK(BM_ByteBufferReader_Next)->Ranges({{64 * 1024, 1024 * 1024}});
+
+static void BM_ByteBufferReader_Peek(benchmark::State& state) {
+  Library::get();
+  const int num_slices = state.range(0);
+  constexpr size_t kSliceSize = 16;
+  std::vector<grpc_slice> slices;
+  for (int i = 0; i < num_slices; ++i) {
+    std::unique_ptr<char[]> buf(new char[kSliceSize]);
+    slices.emplace_back(g_core_codegen_interface->grpc_slice_from_copied_buffer(
+        buf.get(), kSliceSize));
+  }
+  grpc_byte_buffer* bb = g_core_codegen_interface->grpc_raw_byte_buffer_create(
+      slices.data(), num_slices);
+  grpc_byte_buffer_reader reader;
+  GPR_ASSERT(
+      g_core_codegen_interface->grpc_byte_buffer_reader_init(&reader, bb));
+  while (state.KeepRunning()) {
+    grpc_slice* slice;
+    if (GPR_UNLIKELY(!g_core_codegen_interface->grpc_byte_buffer_reader_peek(
+            &reader, &slice))) {
+      g_core_codegen_interface->grpc_byte_buffer_reader_destroy(&reader);
+      GPR_ASSERT(
+          g_core_codegen_interface->grpc_byte_buffer_reader_init(&reader, bb));
+      continue;
+    }
+  }
+
+  g_core_codegen_interface->grpc_byte_buffer_reader_destroy(&reader);
+  g_core_codegen_interface->grpc_byte_buffer_destroy(bb);
+  for (auto& slice : slices) {
+    g_core_codegen_interface->grpc_slice_unref(slice);
+  }
+}
+BENCHMARK(BM_ByteBufferReader_Peek)->Ranges({{64 * 1024, 1024 * 1024}});
+
 }  // namespace testing
 }  // namespace grpc