CodeContext.h

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/*
 * Copyright (C) 1996-2021 The Squid Software Foundation and contributors
 *
 * Squid software is distributed under GPLv2+ license and includes
 * contributions from numerous individuals and organizations.
 * Please see the COPYING and CONTRIBUTORS code_contexts for details.
 */
 
#ifndef SQUID_BASE_CODE_CONTEXT_H
#define SQUID_BASE_CODE_CONTEXT_H
 
#include "base/InstanceId.h"
#include "base/RefCount.h"
 
#include <iosfwd>
 
class CodeContext: public RefCountable
{
public:
    typedef RefCount<CodeContext> Pointer;
 
    static const Pointer &Current();
 
    static void Reset();
 
    static void Reset(const Pointer);
 
    virtual ~CodeContext() {}
 
    virtual ScopedId codeContextGist() const = 0;
 
    virtual std::ostream &detailCodeContext(std::ostream &os) const = 0;
 
private:
    static void ForgetCurrent();
    static void Entering(const Pointer &codeCtx);
    static void Leaving();
};
 
inline
std::ostream &operator <<(std::ostream &os, const CodeContext &ctx)
{
    return os << ctx.codeContextGist();
}
 
/* convenience context-reporting wrappers that also reduce linking problems */
std::ostream &CurrentCodeContextBrief(std::ostream &os);
std::ostream &CurrentCodeContextDetail(std::ostream &os);
 
class CodeContextGuard
{
public:
    CodeContextGuard(const CodeContext::Pointer &newContext): savedCodeContext(CodeContext::Current()) { CodeContext::Reset(newContext); }
    ~CodeContextGuard() { CodeContext::Reset(savedCodeContext); }
 
    // no copying of any kind (for simplicity and to prevent accidental copies)
    CodeContextGuard(CodeContextGuard &&) = delete;
 
    CodeContext::Pointer savedCodeContext;
};
 
template <typename Fun>
inline void
CallBack(const CodeContext::Pointer &callbackContext, Fun &&callback)
{
    // TODO: Consider catching exceptions and letting CodeContext handle them.
    const auto savedCodeContext(CodeContext::Current());
    CodeContext::Reset(callbackContext);
    callback();
    CodeContext::Reset(savedCodeContext);
}
 
template <typename Fun>
inline void
CallService(const CodeContext::Pointer &serviceContext, Fun &&service)
{
    // TODO: Consider catching exceptions and letting CodeContext handle them.
    CodeContextGuard guard(serviceContext);
    service();
}
 
template <typename Fun>
inline void
CallContextCreator(Fun &&creator)
{
    const auto savedCodeContext(CodeContext::Current());
    creator();
    CodeContext::Reset(savedCodeContext);
}
 
 
#endif