Revert "better slice management for win_read"

This reverts commit b0139e15425196be518b251dbdfa3b86648b4740.

src/core/lib/iomgr/tcp_windows.cc

@@ -113,10 +113,7 @@ typedef struct grpc_tcp {
 
   grpc_closure* read_cb;
   grpc_closure* write_cb;
-
-  /* garbage after the last read */
-  grpc_slice_buffer last_read_buffer;
-
+  grpc_slice read_slice;
   grpc_slice_buffer* write_slices;
   grpc_slice_buffer* read_slices;
 
@@ -135,7 +132,6 @@ static void tcp_free(grpc_tcp* tcp) {
   grpc_winsocket_destroy(tcp->socket);
   gpr_mu_destroy(&tcp->mu);
   gpr_free(tcp->peer_string);
-  grpc_slice_buffer_destroy_internal(&tcp->last_read_buffer);
   grpc_resource_user_unref(tcp->resource_user);
   if (tcp->shutting_down) GRPC_ERROR_UNREF(tcp->shutdown_error);
   gpr_free(tcp);
@@ -184,6 +180,7 @@ static void on_read(void* tcpp, grpc_error* error) {
   grpc_tcp* tcp = (grpc_tcp*)tcpp;
   grpc_closure* cb = tcp->read_cb;
   grpc_winsocket* socket = tcp->socket;
+  grpc_slice sub;
   grpc_winsocket_callback_info* info = &socket->read_info;
 
   if (grpc_tcp_trace.enabled()) {
@@ -197,19 +194,11 @@ static void on_read(void* tcpp, grpc_error* error) {
       char* utf8_message = gpr_format_message(info->wsa_error);
       error = GRPC_ERROR_CREATE_FROM_COPIED_STRING(utf8_message);
       gpr_free(utf8_message);
-      grpc_slice_buffer_reset_and_unref_internal(tcp->read_slices);
+      grpc_slice_unref_internal(tcp->read_slice);
     } else {
       if (info->bytes_transfered != 0 && !tcp->shutting_down) {
-        GPR_ASSERT((size_t)info->bytes_transfered <= tcp->read_slices->length);
-        if (static_cast<size_t>(info->bytes_transfered) !=
-            tcp->read_slices->length) {
-          grpc_slice_buffer_trim_end(
-              tcp->read_slices,
-              tcp->read_slices->length -
-                  static_cast<size_t>(info->bytes_transfered),
-              &tcp->last_read_buffer);
-        }
-        GPR_ASSERT((size_t)info->bytes_transfered == tcp->read_slices->length);
+        sub = grpc_slice_sub_no_ref(tcp->read_slice, 0, info->bytes_transfered);
+        grpc_slice_buffer_add(tcp->read_slices, sub);
 
         if (grpc_tcp_trace.enabled()) {
           size_t i;
@@ -225,7 +214,7 @@ static void on_read(void* tcpp, grpc_error* error) {
         if (grpc_tcp_trace.enabled()) {
           gpr_log(GPR_INFO, "TCP:%p unref read_slice", tcp);
         }
-        grpc_slice_buffer_reset_and_unref_internal(tcp->read_slices);
+        grpc_slice_unref_internal(tcp->read_slice);
         error = tcp->shutting_down
                     ? GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING(
                           "TCP stream shutting down", &tcp->shutdown_error, 1)
@@ -239,8 +228,6 @@ static void on_read(void* tcpp, grpc_error* error) {
   GRPC_CLOSURE_SCHED(cb, error);
 }
 
-#define DEFAULT_TARGET_READ_SIZE 8192
-#define MAX_WSABUF_COUNT 16
 static void win_read(grpc_endpoint* ep, grpc_slice_buffer* read_slices,
                      grpc_closure* cb) {
   grpc_tcp* tcp = (grpc_tcp*)ep;
@@ -249,8 +236,7 @@ static void win_read(grpc_endpoint* ep, grpc_slice_buffer* read_slices,
   int status;
   DWORD bytes_read = 0;
   DWORD flags = 0;
-  WSABUF buffers[MAX_WSABUF_COUNT];
-  size_t i;
+  WSABUF buffer;
 
   if (grpc_tcp_trace.enabled()) {
     gpr_log(GPR_INFO, "TCP:%p win_read", tcp);
@@ -266,27 +252,18 @@ static void win_read(grpc_endpoint* ep, grpc_slice_buffer* read_slices,
   tcp->read_cb = cb;
   tcp->read_slices = read_slices;
   grpc_slice_buffer_reset_and_unref_internal(read_slices);
-  grpc_slice_buffer_swap(read_slices, &tcp->last_read_buffer);
 
-  if (tcp->read_slices->length < DEFAULT_TARGET_READ_SIZE / 2 &&
-      tcp->read_slices->count < MAX_WSABUF_COUNT) {
-    // TODO(jtattermusch): slice should be allocated using resource quota
-    grpc_slice_buffer_add(tcp->read_slices,
-                          GRPC_SLICE_MALLOC(DEFAULT_TARGET_READ_SIZE));
-  }
+  tcp->read_slice = GRPC_SLICE_MALLOC(8192);
 
-  GPR_ASSERT(tcp->read_slices->count <= MAX_WSABUF_COUNT);
-  for (i = 0; i < tcp->read_slices->count; i++) {
-    buffers[i].len = (ULONG)GRPC_SLICE_LENGTH(
-        tcp->read_slices->slices[i]);  // we know slice size fits in 32bit.
-    buffers[i].buf = (char*)GRPC_SLICE_START_PTR(tcp->read_slices->slices[i]);
-  }
+  buffer.len = (ULONG)GRPC_SLICE_LENGTH(
+      tcp->read_slice);  // we know slice size fits in 32bit.
+  buffer.buf = (char*)GRPC_SLICE_START_PTR(tcp->read_slice);
 
   TCP_REF(tcp, "read");
 
   /* First let's try a synchronous, non-blocking read. */
-  status = WSARecv(tcp->socket->socket, buffers, (DWORD)tcp->read_slices->count,
-                   &bytes_read, &flags, NULL, NULL);
+  status =
+      WSARecv(tcp->socket->socket, &buffer, 1, &bytes_read, &flags, NULL, NULL);
   info->wsa_error = status == 0 ? 0 : WSAGetLastError();
 
   /* Did we get data immediately ? Yay. */
@@ -298,8 +275,8 @@ static void win_read(grpc_endpoint* ep, grpc_slice_buffer* read_slices,
 
   /* Otherwise, let's retry, by queuing a read. */
   memset(&tcp->socket->read_info.overlapped, 0, sizeof(OVERLAPPED));
-  status = WSARecv(tcp->socket->socket, buffers, (DWORD)tcp->read_slices->count,
-                   &bytes_read, &flags, &info->overlapped, NULL);
+  status = WSARecv(tcp->socket->socket, &buffer, 1, &bytes_read, &flags,
+                   &info->overlapped, NULL);
 
   if (status != 0) {
     int wsa_error = WSAGetLastError();
@@ -353,7 +330,7 @@ static void win_write(grpc_endpoint* ep, grpc_slice_buffer* slices,
   unsigned i;
   DWORD bytes_sent;
   int status;
-  WSABUF local_buffers[MAX_WSABUF_COUNT];
+  WSABUF local_buffers[16];
   WSABUF* allocated = NULL;
   WSABUF* buffers = local_buffers;
   size_t len;
@@ -472,7 +449,6 @@ static void win_shutdown(grpc_endpoint* ep, grpc_error* why) {
 static void win_destroy(grpc_endpoint* ep) {
   grpc_network_status_unregister_endpoint(ep);
   grpc_tcp* tcp = (grpc_tcp*)ep;
-  grpc_slice_buffer_reset_and_unref_internal(&tcp->last_read_buffer);
   TCP_UNREF(tcp, "destroy");
 }
 
@@ -524,7 +500,6 @@ grpc_endpoint* grpc_tcp_create(grpc_winsocket* socket,
   GRPC_CLOSURE_INIT(&tcp->on_read, on_read, tcp, grpc_schedule_on_exec_ctx);
   GRPC_CLOSURE_INIT(&tcp->on_write, on_write, tcp, grpc_schedule_on_exec_ctx);
   tcp->peer_string = gpr_strdup(peer_string);
-  grpc_slice_buffer_init(&tcp->last_read_buffer);
   tcp->resource_user = grpc_resource_user_create(resource_quota, peer_string);
   /* Tell network status tracking code about the new endpoint */
   grpc_network_status_register_endpoint(&tcp->base);