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utils: add observer/observable templates
An observable is used to decouple an information producer from a consumer (in the same way as a callback), while allowing multiple consumers (called observers) to coexist and to manage their lifetime separately. Two classes are introduced: observable: a producer class; when an observable is invoked all observers receive the information observer: a consumer class; receives information from a observable Modelled after boost::signals2, with the following changes - all signals return void; information is passed from the producer to the consumer but not back - thread-unsafe - modern C++ without preprocessor hacks - connection lifetime is always managed rather than leaked by default - renamed to avoid the funky "slot" name Message-Id: <20180709172726.5079-1-avi@scylladb.com>
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/* | ||
* Copyright (C) 2018 ScyllaDB | ||
*/ | ||
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/* | ||
* This file is part of Scylla. | ||
* | ||
* Scylla is free software: you can redistribute it and/or modify | ||
* it under the terms of the GNU Affero General Public License as published by | ||
* the Free Software Foundation, either version 3 of the License, or | ||
* (at your option) any later version. | ||
* | ||
* Scylla is distributed in the hope that it will be useful, | ||
* but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
* GNU General Public License for more details. | ||
* | ||
* You should have received a copy of the GNU General Public License | ||
* along with Scylla. If not, see <http://www.gnu.org/licenses/>. | ||
*/ | ||
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#define BOOST_TEST_MODULE observable_test | ||
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#include <boost/test/unit_test.hpp> | ||
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#include "../utils/observable.hh" | ||
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using namespace utils; | ||
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BOOST_AUTO_TEST_CASE(test_basic_functionality) { | ||
observable<int> pub; | ||
int v1 = 0, v2 = 0; | ||
observer<int> sub1 = pub.observe([&] (int x) { v1 = x; }); | ||
observer<int> sub2 = pub.observe([&] (int x) { v2 = x; }); | ||
pub(7); | ||
BOOST_REQUIRE_EQUAL(v1, 7); | ||
BOOST_REQUIRE_EQUAL(v2, 7); | ||
sub1.disconnect(); | ||
pub(3); | ||
BOOST_REQUIRE_EQUAL(v1, 7); | ||
BOOST_REQUIRE_EQUAL(v2, 3); | ||
sub1 = std::move(sub2); | ||
pub(4); | ||
BOOST_REQUIRE_EQUAL(v1, 7); | ||
BOOST_REQUIRE_EQUAL(v2, 4); | ||
pub = observable<int>(); | ||
pub(5); | ||
BOOST_REQUIRE_EQUAL(v1, 7); | ||
BOOST_REQUIRE_EQUAL(v2, 4); | ||
} | ||
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BOOST_AUTO_TEST_CASE(test_exceptions) { | ||
observable<> pub; | ||
bool saw1 = false; | ||
observer<> sub1 = pub.observe([&] { saw1 = true; }); | ||
observer<> sub2 = pub.observe([&] { throw 2; }); | ||
bool saw3 = false; | ||
observer<> sub3 = pub.observe([&] { saw3 = true; }); | ||
observer<> sub4 = pub.observe([&] { throw 4; }); | ||
bool caught = false; | ||
try { | ||
pub(); | ||
} catch (int v) { | ||
BOOST_REQUIRE(saw1); | ||
BOOST_REQUIRE(saw3); | ||
BOOST_REQUIRE(v == 2 || v == 4); | ||
caught = true; | ||
} | ||
BOOST_REQUIRE(caught); | ||
} |
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/* | ||
* Copyright (C) 2018 ScyllaDB | ||
*/ | ||
|
||
/* | ||
* This file is part of Scylla. | ||
* | ||
* Scylla is free software: you can redistribute it and/or modify | ||
* it under the terms of the GNU Affero General Public License as published by | ||
* the Free Software Foundation, either version 3 of the License, or | ||
* (at your option) any later version. | ||
* | ||
* Scylla is distributed in the hope that it will be useful, | ||
* but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
* GNU General Public License for more details. | ||
* | ||
* You should have received a copy of the GNU General Public License | ||
* along with Scylla. If not, see <http://www.gnu.org/licenses/>. | ||
*/ | ||
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#pragma once | ||
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#include <functional> | ||
#include <vector> | ||
#include <boost/range/algorithm/replace.hpp> | ||
#include <boost/range/algorithm/remove.hpp> | ||
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namespace utils { | ||
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template <typename... Args> | ||
class observable { | ||
public: | ||
class observer; | ||
private: | ||
std::vector<observer*> _observers; | ||
public: | ||
class observer { | ||
friend class observable; | ||
observable* _observable; | ||
std::function<void (Args...)> _callback; | ||
private: | ||
void moved(observer* from) { | ||
if (_observable) { | ||
_observable->moved(from, this); | ||
} | ||
} | ||
public: | ||
observer(observable* o, std::function<void (Args...)> callback) noexcept | ||
: _observable(o), _callback(std::move(callback)) { | ||
} | ||
observer(observer&& o) noexcept | ||
: _observable(std::exchange(o._observable, nullptr)) | ||
, _callback(std::move(o._callback)) { | ||
moved(&o); | ||
} | ||
observer& operator=(observer&& o) noexcept { | ||
if (this != &o) { | ||
disconnect(); | ||
_observable = std::exchange(o._observable, nullptr); | ||
_callback = std::move(o._callback); | ||
moved(&o); | ||
} | ||
return *this; | ||
} | ||
~observer() { | ||
disconnect(); | ||
} | ||
void disconnect() { | ||
if (_observable) { | ||
_observable->destroyed(this); | ||
} | ||
} | ||
}; | ||
friend class observer; | ||
private: | ||
void destroyed(observer* dead) { | ||
_observers.erase(boost::remove(_observers, dead), _observers.end()); | ||
} | ||
void moved(observer* from, observer* to) { | ||
boost::replace(_observers, from, to); | ||
} | ||
void update_observers(observable* ob) { | ||
for (auto&& c : _observers) { | ||
c->_observable = ob; | ||
} | ||
} | ||
public: | ||
observable() = default; | ||
observable(observable&& o) noexcept | ||
: _observers(std::move(o._observers)) { | ||
update_observers(this); | ||
} | ||
observable& operator=(observable&& o) noexcept { | ||
if (this != &o) { | ||
update_observers(nullptr); | ||
_observers = std::move(o._observers); | ||
update_observers(this); | ||
} | ||
return *this; | ||
} | ||
~observable() { | ||
update_observers(nullptr); | ||
} | ||
// Send args to all connected observers | ||
void operator()(Args... args) const { | ||
std::exception_ptr e; | ||
for (auto&& ob : _observers) { | ||
try { | ||
ob->_callback(args...); | ||
} catch (...) { | ||
if (!e) { | ||
e = std::current_exception(); | ||
} | ||
} | ||
} | ||
if (e) { | ||
std::rethrow_exception(std::move(e)); | ||
} | ||
} | ||
// Adds an observer to an observable | ||
observer observe(std::function<void (Args...)> callback) { | ||
observer ob(this, std::move(callback)); | ||
_observers.push_back(&ob); | ||
return ob; | ||
} | ||
}; | ||
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template <typename... Args> | ||
using observer = typename observable<Args...>::observer; | ||
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} |