Mojo: add support for disallowing sync calls for a process.

mojo/public/cpp/bindings/lib/sync_call_restrictions.cc

+// Copyright 2016 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 "mojo/public/cpp/bindings/sync_call_restrictions.h"
+
+#if ENABLE_SYNC_CALL_RESTRICTIONS
+
+#include "base/lazy_instance.h"
+#include "base/logging.h"
+#include "base/threading/thread_local.h"
+#include "mojo/public/c/system/core.h"
+
+namespace mojo {
+
+namespace {
+
+class SyncCallSettings {
+ public:
+  static SyncCallSettings* current();
+
+  bool allowed() const {
+    return scoped_allow_count_ > 0 || system_defined_value_;
+  }
+
+  void IncreaseScopedAllowCount() { scoped_allow_count_++; }
+  void DecreaseScopedAllowCount() {
+    DCHECK_LT(0u, scoped_allow_count_);
+    scoped_allow_count_--;
+  }
+
+ private:
+  SyncCallSettings();
+  ~SyncCallSettings();
+
+  bool system_defined_value_ = true;
+  size_t scoped_allow_count_ = 0;
+};
+
+base::LazyInstance<base::ThreadLocalPointer<SyncCallSettings>>
+    g_sync_call_settings = LAZY_INSTANCE_INITIALIZER;
+
+// static
+SyncCallSettings* SyncCallSettings::current() {
+  SyncCallSettings* result = g_sync_call_settings.Pointer()->Get();
+  if (!result) {
+    result = new SyncCallSettings();
+    DCHECK_EQ(result, g_sync_call_settings.Pointer()->Get());
+  }
+  return result;
+}
+
+SyncCallSettings::SyncCallSettings() {
+  MojoResult result = MojoGetProperty(MOJO_PROPERTY_TYPE_SYNC_CALL_ALLOWED,
+                                      &system_defined_value_);
+  DCHECK_EQ(MOJO_RESULT_OK, result);
+
+  DCHECK(!g_sync_call_settings.Pointer()->Get());
+  g_sync_call_settings.Pointer()->Set(this);
+}
+
+SyncCallSettings::~SyncCallSettings() {
+  g_sync_call_settings.Pointer()->Set(nullptr);
+}
+
+}  // namespace
+
+// static
+void SyncCallRestrictions::AssertSyncCallAllowed() {
+  if (!SyncCallSettings::current()->allowed()) {
+      LOG(FATAL) << "Mojo sync calls are not allowed in this process because "
+                 << "they can lead to jank and deadlock. If you must make an "
+                 << "exception, please see "
+                 << "SyncCallRestrictions::ScopedAllowSyncCall and consult "
+                 << "mojo/OWNERS.";
+  }
+}
+
+// static
+void SyncCallRestrictions::IncreaseScopedAllowCount() {
+  SyncCallSettings::current()->IncreaseScopedAllowCount();
+}
+
+// static
+void SyncCallRestrictions::DecreaseScopedAllowCount() {
+  SyncCallSettings::current()->DecreaseScopedAllowCount();
+}
+
+}  // namespace mojo
+
+#endif  // ENABLE_SYNC_CALL_RESTRICTIONS