Add partial unref

include/grpc/impl/codegen/slice.h

@@ -108,6 +108,10 @@ typedef struct {
   /** the number of slices allocated in the array. External users (i.e any code
    * outside grpc core) MUST NOT use this field */
   size_t capacity;
+  /** the index of the first slice who's memory is still owned by this buffer.
+   * This is only to be used when partially unreffing this slice buffer in
+   * grpc_slice_buffer_partial_reset_and_unref_internal. */
+  size_t idx_of_first_valid_slice;
   /** the combined length of all slices in the array */
   size_t length;
   /** inlined elements to avoid allocations */

src/core/lib/iomgr/tcp_posix.cc

@@ -576,6 +576,8 @@ static bool tcp_flush(grpc_exec_ctx* exec_ctx, grpc_tcp* tcp,
       if (errno == EAGAIN) {
         tcp->outgoing_slice_idx = unwind_slice_idx;
         tcp->outgoing_byte_idx = unwind_byte_idx;
+        grpc_slice_buffer_partial_reset_and_unref_internal(
+            exec_ctx, tcp->outgoing_buffer, unwind_slice_idx);
         return false;
       } else if (errno == EPIPE) {
         *error = grpc_error_set_int(GRPC_OS_ERROR(errno, "sendmsg"),

src/core/lib/slice/slice_buffer.cc

@@ -62,6 +62,7 @@ void grpc_slice_buffer_init(grpc_slice_buffer* sb) {
   sb->count = 0;
   sb->length = 0;
   sb->capacity = GRPC_SLICE_BUFFER_INLINE_ELEMENTS;
+  sb->idx_of_first_valid_slice = 0;
   sb->base_slices = sb->slices = sb->inlined;
 }
 
@@ -166,12 +167,26 @@ void grpc_slice_buffer_pop(grpc_slice_buffer* sb) {
 void grpc_slice_buffer_reset_and_unref_internal(grpc_exec_ctx* exec_ctx,
                                                 grpc_slice_buffer* sb) {
   size_t i;
-  for (i = 0; i < sb->count; i++) {
+  for (i = sb->idx_of_first_valid_slice; i < sb->count; i++) {
     grpc_slice_unref_internal(exec_ctx, sb->slices[i]);
   }
 
   sb->count = 0;
   sb->length = 0;
+  sb->idx_of_first_valid_slice = 0;
+}
+
+void grpc_slice_buffer_partial_reset_and_unref_internal(grpc_exec_ctx* exec_ctx,
+                                                        grpc_slice_buffer* sb,
+                                                        size_t idx) {
+  GPR_ASSERT(idx <= sb->count);
+
+  size_t i;
+  for (i = sb->idx_of_first_valid_slice; i < idx; i++) {
+    grpc_slice_unref_internal(exec_ctx, sb->slices[i]);
+  }
+
+  sb->idx_of_first_valid_slice = idx;
 }
 
 void grpc_slice_buffer_reset_and_unref(grpc_slice_buffer* sb) {

src/core/lib/slice/slice_internal.h

@@ -32,6 +32,9 @@ grpc_slice grpc_slice_ref_internal(grpc_slice slice);
 void grpc_slice_unref_internal(grpc_exec_ctx* exec_ctx, grpc_slice slice);
 void grpc_slice_buffer_reset_and_unref_internal(grpc_exec_ctx* exec_ctx,
                                                 grpc_slice_buffer* sb);
+void grpc_slice_buffer_partial_reset_and_unref_internal(grpc_exec_ctx* exec_ctx,
+                                                        grpc_slice_buffer* sb,
+                                                        size_t idx);
 void grpc_slice_buffer_destroy_internal(grpc_exec_ctx* exec_ctx,
                                         grpc_slice_buffer* sb);