third_party/WebKit/Source/platform/ScriptForbiddenScope.h

// Copyright 2014 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.

#ifndef ScriptForbiddenScope_h
#define ScriptForbiddenScope_h

#include "platform/PlatformExport.h"
#include "wtf/Allocator.h"
#include "wtf/AutoReset.h"
#include "wtf/Optional.h"

namespace blink {

// Scoped disabling of script execution on the main thread,
// and only to be used by the main thread.
class PLATFORM_EXPORT ScriptForbiddenScope final {
    STACK_ALLOCATED();
    WTF_MAKE_NONCOPYABLE(ScriptForbiddenScope);
public:
    ScriptForbiddenScope() { enter(); }
    ~ScriptForbiddenScope() { exit(); }

    class PLATFORM_EXPORT AllowUserAgentScript final {
        STACK_ALLOCATED();
        WTF_MAKE_NONCOPYABLE(AllowUserAgentScript);
    public:
        AllowUserAgentScript()
        {
            if (isMainThread())
                m_change.emplace(&s_scriptForbiddenCount, 0);
        }
        ~AllowUserAgentScript()
        {
            DCHECK(!isMainThread() || !s_scriptForbiddenCount);
        }

    private:
        Optional<AutoReset<unsigned>> m_change;
    };

    static void enter()
    {
        DCHECK(isMainThread());
        ++s_scriptForbiddenCount;
    }
    static void exit()
    {
        DCHECK(s_scriptForbiddenCount);
        --s_scriptForbiddenCount;
    }
    static bool isScriptForbidden()
    {
        return isMainThread() && s_scriptForbiddenCount;
    }

private:
    static unsigned s_scriptForbiddenCount;
};

// Scoped disabling of script execution on the main thread,
// if called on the main thread.
//
// No effect when used by from other threads -- simplifies
// call sites that might be used by multiple threads to have
// this scope object perform the is-main-thread check on
// its behalf.
class PLATFORM_EXPORT ScriptForbiddenIfMainThreadScope final {
    STACK_ALLOCATED();
    WTF_MAKE_NONCOPYABLE(ScriptForbiddenIfMainThreadScope);
public:
    ScriptForbiddenIfMainThreadScope()
    {
        m_IsMainThread = isMainThread();
        if (m_IsMainThread)
            ScriptForbiddenScope::enter();
    }
    ~ScriptForbiddenIfMainThreadScope()
    {
        if (m_IsMainThread)
            ScriptForbiddenScope::exit();
    }
    bool m_IsMainThread;
};

} // namespace blink

#endif // ScriptForbiddenScope_h