source: src/Common/GC.h@ 6fa409e

//
// Cforall Version 1.0.0 Copyright (C) 2015 University of Waterloo
//
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// GC.h --
//
// Author           : Aaron B. Moss
// Created On       : Thu Mar 15 14:47:00 2018
// Last Modified By : Aaron B. Moss
// Last Modified On : Thu Mar 15 14:47:00 2018
// Update Count     : 1
//

#pragma once

#include <cassert>
#include <vector>

class GC_Object;
class BaseSyntaxNode;
class GC_Guard;

/// Manually traced and called garbage collector
class GC {
        friend class GcTracer;
        friend class GC_Guard;

        /// Collects the youngest generation, placing survivors in previous generation.
        /// Young generation objects cannot be kept alive by pointers from older generation.
        /// Older generation is used for subsequent new objects.
        void collect_young();
public:
        /// Gets singleton GC instance
        static GC& get();

        /// Traces a traceable object
        const GC& operator<< (const GC_Object*) const;

        /// No-trace mark; returns true if the object exists and was not already marked
        bool notrace_mark(const GC_Object*) const;

        /// Adds a new object to garbage collection
        void register_object(GC_Object*);

        /// Adds an object to the set of static roots
        void register_static_root(BaseSyntaxNode*);

        /// Start new generation for subsequent new objects
        GC_Guard new_generation();

        /// Traces all static roots
        void trace_static_roots();

        /// Collects oldest generation; use oldest generation afterward.
        /// Error if currently using younger generation
        void collect();

        /// Collects all contained objects
        ~GC();

private:
        GC();

        using Generation = std::vector<GC_Object*>;
        std::vector<Generation> gens;  ///< Set of generations; always at least one

        using StaticRoots = std::vector<BaseSyntaxNode*>;
        StaticRoots static_roots;      ///< Set of static-lifetime roots

        bool mark;                     ///< The current collection's mark bit
        unsigned g;                    ///< The current number generation in use

        /// Trace a traceable object (enabled by SFINAE)
        template<typename T>
        static inline auto do_trace(const GC& gc, T& obj, int) -> decltype(gc << obj, void()) {
                gc << obj;
        }

        /// Do not trace an untraceable object
        template<typename T>
        static inline auto do_trace(const GC&, T&, long) -> void {}

        /// Base case for maybe_trace
        void maybe_trace() const {}

public:
        /// Trace any objects that are traceable
        template<typename T, typename... Args>
        void maybe_trace(T& obj, Args&... args) const {
                // uses SFINAE trick to select proper overload; prefers actually tracing version 
                // (because of int->long conversion), but will fall back to non-tracing
                do_trace(*this, obj, 0);
                maybe_trace(args...);
        }
};

/// Cleanup object for young generation
class GC_Guard {
        friend class GC;

        GC& gc;      ///< GC associated with
        unsigned g;  ///< Generation constructed for

        GC_Guard( GC& gc, unsigned g ) : gc(gc), g(g) {}

public:
        ~GC_Guard() {
                assert( gc.g == g && "collecting current generation" );
                gc.collect_young();
        }
};

/// Use young generation until next collection
inline GC_Guard new_generation() { return GC::get().new_generation(); }

// /// no-op default trace
// template<typename T>
// inline const GC& operator<< (const GC& gc, const T& x) { return gc; }

inline void traceAll(const GC&) {}

/// Marks all arguments as live in current generation
template<typename T, typename... Args>
inline void traceAll(const GC& gc, T& x, Args&... xs) {
        gc << x;
        traceAll(gc, xs...);
}

/// Traces roots without collecting
template<typename... Args>
inline void trace(Args&... roots) {
        GC& gc = GC::get();
        traceAll(gc, roots...);
}

/// Traces roots and collects other elements; should not be any young generations live
template<typename... Args>
inline void collect(Args&... roots) {
        GC& gc = GC::get();
        traceAll(gc, roots...);
        gc.collect();
}

/// Makes a new expression as a static root
template<typename T, typename... Args>
inline T* new_static_root( Args&&... args ) {
        T* root = new T( std::forward<Args>(args)... );
        GC::get().register_static_root( root );
        return root;
}

/// Class that is managed by the GC
class GC_Object {
        friend class GC;
protected:
        mutable bool mark;

        // Override default constructors to ensure clones are registered and properly marked
        GC_Object();

        GC_Object(const GC_Object&);

        GC_Object(GC_Object&&);

        GC_Object& operator= (const GC_Object&) { /* do not assign mark */ return *this; }

        GC_Object& operator= (GC_Object&&) { /* do not assign mark */ return *this; }

        // Ensure subclasses can be deleted by garbage collector
        virtual ~GC_Object() {}

        /// override to trace any child objects
        virtual void trace(const GC&) const {}
};

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// compile-command: "make install" //
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