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libglim is an Apache-licensed C++ wrapper for lmdb, and rather than rolling our own it seems prudent to use it. Note: lmdb is not included in it, and unless something happens as did with libunbound, should be installed via each OS' package manager or equivalent.
237 lines
12 KiB
C++
237 lines
12 KiB
C++
#ifndef _GLIM_SERIALIZABLEPOOL_HPP_INCLUDED
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#define _GLIM_SERIALIZABLEPOOL_HPP_INCLUDED
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#include "gstring.hpp"
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#ifndef _SERIALIZABLEPOOL_NOLDB
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# include "ldb.hpp" // Reuse `ldbSerialize` and `ldbDeserialize` in the `with` method.
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#endif
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namespace glim {
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namespace SerializablePoolHelpers {
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struct Impl {
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/**
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* Pool format: \code
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* uint32_t valuesStart; // Network byte order.
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* uint32_t value0Offset, value1Offset, ... valueNOffset; // Network byte order.
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* char value0[]; char zero; char value1[]; char zero; ... char valueN[]; char zero;
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* \endcode
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*/
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gstring _pool;
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std::vector<gstring> _changes;
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std::vector<bool> _changed;
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bool _readOnly = false;
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Impl() = default;
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Impl (const gstring& poolBytes): _pool (poolBytes), _readOnly (false) {}
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};
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/// Can be used to avoid a deep copy of the pool and change vectors (pImpl idiom).
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/// Example: \code glim::SerializablePool pool; \endcode
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struct SharedPtr {
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std::shared_ptr<Impl> _impl;
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SharedPtr() = default;
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SharedPtr (const gstring& poolBytes): _impl (std::make_shared<Impl> (poolBytes)) {}
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Impl* get() const {return _impl.get();}
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Impl* operator->() const {return _impl.get();}
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Impl& operator*() const {return *_impl;}
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Impl* instance() {if (!_impl) _impl = std::make_shared<Impl>(); return _impl.get();}
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};
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/// Can be used instead of SharedPtr to avoid the shared_ptr indirection when the SerializablePoolTpl isn't going to be copied.
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/// Example: \code glim::InlineSerializablePool temporaryPool (bytes); \endcode
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struct InlinePtr {
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Impl _impl;
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InlinePtr() = default;
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InlinePtr (const gstring& poolBytes): _impl (poolBytes) {}
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Impl* get() const {return const_cast<Impl*> (&_impl);}
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Impl* operator->() const {return const_cast<Impl*> (&_impl);}
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Impl& operator*() const {return const_cast<Impl&> (_impl);}
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Impl* instance() {return &_impl;}
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};
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}
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/** Serialization with lazy parsing: fields are accessed without "unpacking" the byte array.
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* Changes are stored separately, allowing the user to know exactly what fields has been changed and compare the old values to the new ones. */
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template <typename PI>
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class SerializablePoolTpl {
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protected:
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using Impl = SerializablePoolHelpers::Impl;
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PI _impl;
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/** @param ref Return a zero-copy view. The view should not be used outside of the pool buffer's lifetime. */
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static gstring original (const gstring& pool, uint32_t num, bool ref = false) {
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uint32_t poolLength = pool.length(); if (poolLength < 4) return gstring();
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uint32_t valuesStart = ntohl (*(uint32_t*) pool.data());
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assert (valuesStart <= poolLength);
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uint32_t valueOffsetOffset = 4 + num * 4;
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if ((int) valuesStart - (int) valueOffsetOffset < 4) return gstring(); // num > size
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uint32_t valueOffset = ntohl (*(uint32_t*) (pool.data() + valueOffsetOffset));
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valueOffsetOffset += 4;
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uint32_t nextValueOffset = ((int) valuesStart - (int) valueOffsetOffset < 4)
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? poolLength
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: ntohl (*(uint32_t*) (pool.data() + valueOffsetOffset));
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return gstring (0, (void*) (pool.data() + valueOffset), false, nextValueOffset - 1 - valueOffset, ref);
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}
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/** How many elements are in the pool. */
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static uint32_t poolSize (const gstring& pool) {
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if (pool.length() < 4) return 0;
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uint32_t valuesStart = ntohl (*(uint32_t*) pool.data());
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return (valuesStart - 4) / 4;
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}
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void toBytes (gstring& newPool, uint32_t size, const gstring* oldPool) const {
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newPool.clear();
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const Impl* impl = _impl.get();
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const std::vector<bool>& changed = impl->_changed;
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const std::vector<gstring>& changes = impl->_changes;
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if (changed.empty()) return;
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uint32_t valuesStart = 4 + size * 4;
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uint32_t networkOrder = 0;
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newPool.append ((char*) &(networkOrder = htonl (valuesStart)), 4);
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for (uint32_t num = 0; num < size; ++num) newPool.append ((char*) &(networkOrder = 0), 4);
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for (uint32_t num = 0; num < size; ++num) {
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uint32_t start = newPool.length();
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if (num < changed.size() && changed[num]) newPool << changes[num];
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else newPool << original (oldPool ? *oldPool : impl->_pool, num);
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newPool << '\0';
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uint32_t valuesOffsetOffset = 4 + num * 4; assert (valuesOffsetOffset < valuesStart);
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*(uint32_t*)(newPool.data() + valuesOffsetOffset) = htonl (start);
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}
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}
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public:
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/** Field, old value, new value. Might be used to maintain indexes. */
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typedef std::function<void(uint32_t, const gstring&, const gstring&)> ChangeVisitor;
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SerializablePoolTpl() = default;
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/** Copy the given pool bytes from the outside source (e.g. from the database). */
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SerializablePoolTpl (const gstring& poolBytes): _impl (poolBytes) {}
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/** Returns a view into the original serialized field (ignores the current changes).\n
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* Returns an empty string if the field is not in the pool (num > size).
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* @param ref Return a zero-copy view. The view becomes invalid after the value has been changed or when the pool's `Impl` is destroyed. */
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const gstring original (uint32_t num, bool ref = false) const {return original (_impl->_pool, num, ref);}
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/** Returns the original serialized field (ignores the current changes).\n
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* Returns an empty string if the field is not in the pool (num > size). */
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const char* cstringOriginal (uint32_t num) const {
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gstring gs (original (_impl->_pool, num));
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return gs.empty() ? "" : gs.data(); // All fields in the _pool are 0-terminated.
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}
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/** Returns the field.
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* @param ref Return a zero-copy view. The view becomes invalid after the value has been changed or when the pool's `Impl` is destroyed. */
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const gstring current (uint32_t num, bool ref = false) const {
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const Impl* impl = _impl.get(); if (!impl) return gstring();
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if (num < impl->_changed.size() && impl->_changed[num]) {
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const gstring& value = impl->_changes[num]; return ref ? value.ref() : value;}
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return original (impl->_pool, num);
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}
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/** Set the new value of the field. */
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void set (uint32_t num, const gstring& value) {
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Impl* impl = _impl.instance();
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if (__builtin_expect (impl->_readOnly, 0)) throw std::runtime_error ("Attempt to modify a read-only SerializablePool");
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if (num >= impl->_changed.size()) {impl->_changed.resize (num + 1); impl->_changes.resize (num + 1);}
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impl->_changed[num] = true;
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impl->_changes[num] = value;
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}
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void reserve (uint32_t fields) {
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Impl* impl = _impl.instance();
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if (__builtin_expect (impl->_readOnly, 0)) throw std::runtime_error ("Attempt to modify a read-only SerializablePool");
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impl->_changed.reserve (fields);
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impl->_changes.reserve (fields);
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}
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/** Peek into the pool.\n
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* Returned reference should not be used after the SerializablePool goes out of scope (and destroyed). */
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const gstring& originalPool() {return _impl->_pool;}
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/** Serialize the pool.
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* @param changeVisitor is called for every field that was really changed (e.g. the bytes differ). */
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void toBytes (gstring& newPool, ChangeVisitor changeVisitor = ChangeVisitor()) const {
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if (changeVisitor) {
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const Impl* impl = _impl.get();
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const std::vector<bool>& changed = impl->_changed;
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const std::vector<gstring>& changes = impl->_changes;
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for (uint32_t num = 0, size = changed.size(); num < size; ++num) if (changed[num]) {
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const gstring& from = original (impl->_pool, num); const gstring& to = changes[num];
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if (from != to) changeVisitor (num, from, to);
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}
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}
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toBytes (newPool, (uint32_t) _impl->_changed.size(), nullptr);
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}
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/**
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* Performs "delta" serialization of the pool: creates a new pool where values which has not changed are copied from the `oldPool`.\n
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* \code Use case: 1) pools X and Y are loaded from a database by users A and B;
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* 2) user A changes field 0 in pool X; 3) user B changes field 1 in pool Y;
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* 4) user A loads `oldPool` from the database, does `toBytesDelta` from pool X and saves to the database;
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* 5) user B loads `oldPool` from the database, does `toBytesDelta` from pool Y and saves to the database;
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* result: database contains both changes (field 0 from user A and field 1 from user B). \endcode
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* @param changeVisitor is called for every field that was changed between the oldPool and the current one.
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* Returns `false` and leaves `newPool` *empty* if there are no changes found against the `oldPool`.
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*/
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bool toBytesDelta (gstring& newPool, const gstring& oldPool, ChangeVisitor changeVisitor = ChangeVisitor()) const {
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newPool.clear();
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const Impl* impl = _impl.get();
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const std::vector<bool>& changed = impl->_changed;
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const std::vector<gstring>& changes = impl->_changes;
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bool verifiedChanges = false;
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for (uint32_t num = 0, size = changed.size(); num < size; ++num) if (changed[num]) {
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const gstring& from = original (oldPool, num); const gstring& to = changes[num];
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if (from != to) {
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verifiedChanges = true;
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if (changeVisitor) changeVisitor (num, from, to); else break;
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}
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}
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if (!verifiedChanges) return false;
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toBytes (newPool, std::max ((uint32_t) changed.size(), poolSize (oldPool)), &oldPool);
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return true;
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}
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/** True if the field has been `set` in this pool instance.\n
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* NB: Does *not* check if the `set` value is equal to the `original` value or not. */
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bool changed (uint32_t num) const {const auto& changed = _impl->_changed; return num < changed.size() ? changed[num] : false;}
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/** True if a field has been `set` in this pool instance. */
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bool changed() const {return !_impl->_changed.empty();}
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bool operator == (const SerializablePoolTpl<PI>& rhs) const {return _impl.get() == rhs._impl.get();}
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/** Useful for storing SerializablePool in a map. */
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intptr_t implId() const {return (intptr_t) _impl.get();}
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/** If set to `true` then modifying the pool will throw an exception.\n
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* Useful for freezing the pool before sharing it with other threads. */
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void readOnly (bool ro) {if (_impl) _impl->_readOnly = true;}
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bool readOnly() const {return (_impl ? _impl->_readOnly : false);}
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/** Number of elements in the pool. Equals to max(num)-1. */
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uint32_t size() const {
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Impl* impl = _impl.get(); if (__builtin_expect (!impl, 0)) return 0;
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return std::max (poolSize (impl->_pool), (uint32_t) impl->_changed.size());
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}
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#ifndef _SERIALIZABLEPOOL_NOLDB
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/** Serialize the `value` with `ldbSerialize` and `set` it to `num`.
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* @param stackSize is the amount of space to preallocate on stack for the temporary buffer. */
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template<typename T> void serialize (uint32_t num, const T& value, uint32_t stackSize = 256) {
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GSTRING_ON_STACK (bytes, stackSize);
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ldbSerialize (bytes, value);
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set (num, bytes);
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}
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/** If the field is not empty then `ldbDeserialize` it into `value`. */
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template<typename T> void deserialize (uint32_t num, T& value) const {
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const gstring& bytes = current (num);
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if (bytes.length()) ldbDeserialize (current (num), value);
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}
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/** Deserialize the `num` field with `ldbDeserialize`, run `visitor` on it, then optionally serialize the field back using `ldbSerialize`.
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* Example: \code
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* typedef std::map<std::string, std::string> MyMap;
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* pool.with<MyMap> (_myMap, [](MyMap& myMap) {myMap["foo"] = "bar"; return true;});
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* \endcode
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* @param visitor must return `true` to serialize the field back to the pool.
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*/
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template<typename T> void with (uint32_t num, std::function<bool(T&)> visitor) {
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const gstring& fromBytes = current (num, true);
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T value; if (fromBytes.length()) ldbDeserialize (fromBytes, value);
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if (visitor (value)) serialize (num, value, 16 + fromBytes.length() * 2);
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}
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#endif
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};
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using SerializablePool = SerializablePoolTpl<SerializablePoolHelpers::SharedPtr>;
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using InlineSerializablePool = SerializablePoolTpl<SerializablePoolHelpers::InlinePtr>;
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}
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#endif // _GLIM_SERIALIZABLEPOOL_HPP_INCLUDED
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