SelectionOwner: add support for TIMESTAMP target

ui/base/x/selection_owner.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/base/x/selection_owner.h"
 
 #include <algorithm>
 #include <X11/Xlib.h>
 #include <X11/Xatom.h>
 
 #include "base/logging.h"
 #include "ui/base/x/selection_utils.h"
 #include "ui/base/x/x11_foreign_window_manager.h"
 #include "ui/base/x/x11_util.h"
+#include "ui/events/platform/x11/x11_event_source.h"
 
 namespace ui {
 
 namespace {
 
 const char kAtomPair[] = "ATOM_PAIR";
 const char kIncr[] = "INCR";
 const char kMultiple[] = "MULTIPLE";
 const char kSaveTargets[] = "SAVE_TARGETS";
 const char kTargets[] = "TARGETS";
+const char kTimestamp[] = "TIMESTAMP";
 
-const char* kAtomsToCache[] = {
-  kAtomPair,
-  kIncr,
-  kMultiple,
-  kSaveTargets,
-  kTargets,
-  NULL
-};
+const char* kAtomsToCache[] = {kAtomPair, kIncr,      kMultiple, kSaveTargets,
+                               kTargets,  kTimestamp, NULL};
 
 // The period of |incremental_transfer_abort_timer_|. Arbitrary but must be <=
 // than kIncrementalTransferTimeoutMs.
 const int kTimerPeriodMs = 1000;
 
 // The amount of time to wait for the selection requestor to process the data
 // sent by the selection owner before aborting an incremental data transfer.
 const int kIncrementalTransferTimeoutMs = 10000;
 
 static_assert(kTimerPeriodMs <= kIncrementalTransferTimeoutMs,
@@ skipping 71 matching lines @@
 
 void SelectionOwner::RetrieveTargets(std::vector<XAtom>* targets) {
   for (SelectionFormatMap::const_iterator it = format_map_.begin();
        it != format_map_.end(); ++it) {
     targets->push_back(it->first);
   }
 }
 
 void SelectionOwner::TakeOwnershipOfSelection(
     const SelectionFormatMap& data) {
+  // Save the last server timestamp seen from X, to satisfy requests for the
+  // TIMESTAMP target later…
+  acquired_selection_timestamp_ =
+      X11EventSource::GetInstance()->last_seen_server_time();
+  // …but always pass CurrentTime to XSetSelectionOwner to increase the chances
+  // of this succeeding.
   XSetSelectionOwner(x_display_, selection_name_, x_window_, CurrentTime);

[dcheng, 2016/04/20 00:55:26]

For whatever reason, using last_seen_server_time() causes XSetSelectionOwner()
to fail randomly. So even though we grab a timestamp from X, we always pass
CurrentTime here to make it more likely that it will succeed.

 
   if (XGetSelectionOwner(x_display_, selection_name_) == x_window_) {
     // The X server agrees that we are the selection owner. Commit our data.
     format_map_ = data;
   }
 }
 
 void SelectionOwner::ClearSelectionOwner() {
   XSetSelectionOwner(x_display_, selection_name_, None, CurrentTime);
   format_map_ = SelectionFormatMap();
@@ skipping 76 matching lines @@
   if (!it->data.get())
     CompleteIncrementalTransfer(it);
 }
 
 bool SelectionOwner::ProcessTarget(XAtom target,
                                    XID requestor,
                                    XAtom property) {
   XAtom multiple_atom = atom_cache_.GetAtom(kMultiple);
   XAtom save_targets_atom = atom_cache_.GetAtom(kSaveTargets);
   XAtom targets_atom = atom_cache_.GetAtom(kTargets);
+  XAtom timestamp_atom = atom_cache_.GetAtom(kTimestamp);
 
   if (target == multiple_atom || target == save_targets_atom)
     return false;
 
-  if (target == targets_atom) {
+  if (target == timestamp_atom) {
+    XChangeProperty(
+        x_display_, requestor, property, XA_INTEGER, 32, PropModeReplace,
+        reinterpret_cast<unsigned char*>(&acquired_selection_timestamp_), 1);
+    return true;
+  } else if (target == targets_atom) {
     // We have been asked for TARGETS. Send an atom array back with the data
     // types we support.
     std::vector<XAtom> targets;
+    targets.push_back(timestamp_atom);
     targets.push_back(targets_atom);
     targets.push_back(save_targets_atom);
     targets.push_back(multiple_atom);
     RetrieveTargets(&targets);
 
     XChangeProperty(x_display_, requestor, property, XA_ATOM, 32,
                     PropModeReplace,
                     reinterpret_cast<unsigned char*>(&targets.front()),
                     targets.size());
     return true;
@@ skipping 136 matching lines @@
       foreign_window_manager_id(foreign_window_manager_id) {
 }
 
 SelectionOwner::IncrementalTransfer::IncrementalTransfer(
     const IncrementalTransfer& other) = default;
 
 SelectionOwner::IncrementalTransfer::~IncrementalTransfer() {
 }
 
 }  // namespace ui