{"id":2950,"date":"2019-03-11T22:21:14","date_gmt":"2019-03-11T14:21:14","guid":{"rendered":"https:\/\/damogame.cn:15443\/wordpress\/?p=2950"},"modified":"2019-03-11T22:31:08","modified_gmt":"2019-03-11T14:31:08","slug":"c%e5%b9%b6%e5%8f%91%e5%9e%8b%e6%a8%a1%e5%bc%8f3-%e7%ad%89%e5%be%85%e5%bc%82%e6%ad%a5%e6%93%8d%e4%bd%9c%e7%bb%93%e6%9e%9c-future-promise","status":"publish","type":"post","link":"https:\/\/i007.cc\/wordpress\/archives\/2950","title":{"rendered":"C++\u5e76\u53d1\u578b\u6a21\u5f0f#3: \u7b49\u5f85\u5f02\u6b65\u64cd\u4f5c\u7ed3\u679c – future\/promise"},"content":{"rendered":"

future\/promise\u7684\u5f15\u5165<\/h2>\n

\u521a\u5f00\u59cb\u5b66\u4e60\u7ebf\u7a0b\u5e93\u65f6, \u6211\u4eec\u4e5f\u8bb8\u90fd\u4f1a\u5410\u69fd\u4e3a\u4ec0\u4e48\u7ebf\u7a0b\u6ca1\u6709\u4e2a\u8fd4\u56de\u503c\u8ba9\u6211\u8fd4\u56de\u7ed3\u679c, \u540e\u6765\u6211\u4eec\u77e5\u9053\u53ef\u4ee5\u7528\u6761\u4ef6\u53d8\u91cf\u6765\u505a:<\/p>\n

\n
boost::mutex g_mtx;\r\nboost::condition_variable g_cond;\r\nint result = 233;\r\n\r\nvoid calculate_the_answer_to_life_the_universe_and_everything() {\r\n     boost::unique_lock<boost::mutex> lock(g_mtx);\r\n     result = 42;\r\n     g_cond.notify_all();\r\n}\r\n\r\nint main() {\r\n     boost::thread tr1(calculate_the_answer_to_life_the_universe_and_everything);\r\n     \/\/ do something\r\n     boost::unique_lock<boost::mutex> lock(g_mtx);\r\n     g_cond.wait(lock);\r\n     assert(result == 42);\r\n     \/\/ do something else\r\n     tr1.join();\r\n     return 0;\r\n}<\/pre>\n
 <\/p>\n<\/div>\n
\u8fd9\u79cd\u5199\u6cd5\u5f53\u7136\u662f\u80fd\u62ff\u5230\u7ed3\u679c\u7684, \u4f46\u662f\u6709\u51e0\u4e2a\u95ee\u9898:<\/p>\n
    \n
  1. \u4e0d\u5bb9\u6613\u5e94\u4ed8\u5f02\u5e38, notify\u4e4b\u524d\u7ed9\u629b\u5f02\u5e38\u4e86, \u53e6\u4e00\u8fb9\u5c31\u4f1a\u4e00\u76f4\u7b49.<\/li>\n
  2. \u6bcf\u4e2a\u201d\u8fd4\u56de\u503c\u201d\u90fd\u9700\u8981\u4e00\u4e2amutex, \u4e00\u4e2a\u53d8\u91cf\u7528\u4e8e\u50a8\u5b58, \u4e00\u4e2a\u6761\u4ef6\u53d8\u91cf, \u7528\u7684\u591a\u4e86, \u4f20\u53c2\u6570\u5c31\u5f88\u9ebb\u70e6, \u4e5f\u5bb9\u6613\u6709\u91cd\u590d\u4ee3\u7801.<\/li>\n
  3. \u6ca1\u5904\u7406\u610f\u5916\u5524\u9192, \u8981\u5904\u7406\u8fd8\u5f97\u52a0\u4e2aflag, \u95ee\u98982\u66f4\u4e25\u91cd\u4e86.<\/li>\n
  4. notify\u9519\u4e86, \u5fd8\u8bb0notify\u4e86, \u5fd8\u8bb0\u52a0\u9501\u4e86\u2026\u4e0d\u719f\u6089\u6761\u4ef6\u53d8\u91cf\u4f7f\u7528\u5f15\u53d1\u7684\u95ee\u9898\u5c31\u66f4\u4e00\u8a00\u96be\u5c3d\u4e86, \u4e0a\u9762\u8fd9\u4ee3\u7801\u8bf4\u4e0d\u5b9a\u8fd8\u662f\u9519\u7684.<\/li>\n<\/ol>\n
    \u6240\u4ee5\u8bf4\u4e3a\u4e86\u4e00\u4e2a\u201d\u8fd4\u56de\u503c\u201d\u505a\u8fd9\u4e48\u591a\u4e8b\u60c5\u771f\u7684\u5f88\u4e0d\u503c\u5f97, \u4e8e\u662f\u5f88\u81ea\u7136\u7684, \u6211\u4eec\u4f1a\u60f3\u628a\u4e0a\u9762\u8fd9\u4e9b\u4e8b\u60c5\u5c01\u88c5\u8d77\u6765, \u5f53\u7136, \u5c01\u88c5\u4ec0\u4e48\u7684\u524d\u4eba\u5df2\u7ecf\u505a\u4e86, \u6bd4\u5982C++\u6807\u51c6\u5e93\u4e2d\u4f7f\u7528future\/promise\u5bf9\u8fd9\u4e00\u7c7b\u4e8b\u60c5\u5efa\u6a21, \u524d\u8005\u7ed9\u6d88\u8d39\u8005\u7528(wait), \u540e\u8005\u7ed9\u751f\u4ea7\u8005\u7528(notify). \u5728\u6210\u4e3a\u6807\u51c6\u524d, boost1.41\u6700\u65e9\u5f15\u5165\u4e86future\/promise[1], \u4f7f\u7528future\/promise\u7684\u8bdd, \u6211\u4eec\u53ef\u4ee5\u7b80\u5316\u4e0a\u8ff0\u4ee3\u7801:<\/p>\n
    \n
    void calculate_the_answer_to_life_the_universe_and_everything(boost::promise<int>& ret) {\r\n     ret.set_value(42);\r\n}\r\n\r\nint main() {\r\n     boost::promise<int> pr;\r\n     boost::unique_future<int> f = pr.get_future();\r\n     boost::thread tr1(thread_func, boost::ref(pr));\r\n     \/\/ do something\r\n     assert(f.get() == 42);\r\n     \/\/ do something else\r\n     tr1.join();\r\n     return 0;\r\n}<\/pre>\n
     <\/p>\n<\/div>\n
    \u597d\u591a\u4e86, \u95ee\u98982,3,4\u770b\u8d77\u6765\u662f\u89e3\u51b3\u4e86, \u4f46\u662f\u5f02\u5e38\u8fd8\u662f\u6ca1\u5904\u7406, \u5f53\u7136promise\u4e5f\u6ca1\u795e\u5947\u5230\u53ef\u4ee5\u5e2e\u4f60\u6355\u83b7\u5f02\u5e38, \u5b83\u53ea\u662f\u7ed9\u4f60\u00a0set_exception\u00a0<\/span><\/code>\u628a\u5f02\u5e38\u4fdd\u5b58\u8d77\u6765, \u7136\u540e\u53e6\u4e00\u8fb9\u4f60\u8c03\u7528future.get()\u7684\u65f6\u5019\u518d\u629b\u51fa.\u00a0try<\/span>...<\/span>catch<\/span>\u00a0<\/span><\/code>\u8fd8\u662f\u5f97\u81ea\u5df1\u5199\u7684. \u8981\u4e0d\u60f3\u81ea\u5df1\u00a0try_catch\u00a0<\/span><\/code>\u4e5f\u884c, \u6211\u4eec\u540e\u9762\u8bb2.<\/p>\n
    boost\u4e2d\u7684future\/promise\u5b9e\u73b0<\/h2>\n
    future\/promise\u7684\u6700\u65e9\u57281970\u5e74\u4ee3\u5c31\u5df2\u7ecf\u63d0\u51fa,\u00a0C++\u8fd8\u4e0d\u77e5\u9053\u5728\u54ea\u5462\u00a0<\/del>, \u4e0d\u540c\u8bed\u8a00\u4e2d\u7684\u5b9e\u73b0\u591a\u5c11\u6709\u4e0d\u4e00\u6837, C++\u4e2d\u662f\u901a\u8fc7\u5e93\u5b9e\u73b0\u7684, boost\u662f1.41\u5f15\u5165\u7684\u7b2c\u4e00\u7248, \u57fa\u4e8emutex\/condition_variable, \u4ee3\u7801\u6bd4\u8f83\u7b80\u6d01, \u4e0b\u9762\u6211\u4eec\u4e5f\u662f\u6839\u636e\u8fd9\u4e2a\u7248\u672c\u6765\u91cd\u590d\u9020\u8f6e\u5b50. STL\u7684\u5b9e\u73b0\u53ef\u80fd\u4f1a\u4e0e\u5e73\u53f0\u6709\u5173, \u6bd4\u5982GCC\u7684STL\u91cc\u7684\u5b9e\u73b0\u5c31\u662f\u57fa\u4e8efutex\u7684, \u800cMSVC\u5374\u53c8\u662f\u57fa\u4e8emutex\/condition_variable.<\/p>\n
    boost\u4e2dshared_future\u548cunique_future\u90fd\u662f\u5bf9future_object\u7684\u5305\u88c5, \u800c\u8fd9\u4e2afuture_object\u5219\u662fmutex\/condition_variable\/flag\u7684\u6301\u6709\u8005, \u771f\u6b63\u7684\u5b9e\u73b0\u4e3b\u4f53. \u65e2\u7136\u5b9e\u73b0\u4e3b\u4f53\u5728future_object, \u6211\u4eec\u5c31\u6682\u4e14\u5c06\u4e4b\u653e\u5230\u540e\u9762, \u5148\u770bpromise.<\/p>\n
    promise<\/h3>\n
    promise\u4e00\u822c\u4e0d\u53ef\u590d\u5236, \u53ef\u4ee5get_future, set_value\u662f\u5176\u4e3b\u8981\u63a5\u53e3, \u5f02\u5e38\u5904\u7406\u65b9\u9762, \u6709set_exception, \u7279\u522b\u5730, promise\u6790\u6784\u7684\u65f6\u5019, \u5982\u679c\u6ca1\u6709set\u8fc7value, \u90a3\u4e48\u5c31\u4f1a\u8bbe\u4e00\u4e2abroken_promise\u7684\u5f02\u5e38. \u5ffd\u7565\u79fb\u52a8\u8bed\u4e49, promise\u7684\u63a5\u53e3\u53ef\u4ee5\u5982\u4e0b:<\/p>\n
    \n
    template<typename T>\r\nclass unique_future;\r\n\r\ntemplate<typename T>\r\nclass promise {\r\nprivate:\r\n       promise(const promise& rhs); \/\/ = delete\r\n       promise& operator=(promise& rhs) \/\/ = delete\r\npublic:\r\n       promise();\r\n       ~promise();\r\n       unique_future<T> get_future();\r\n       void set_value(const T& value);\r\n       void set_exception(boost::exceptional_ptr p);\r\n};<\/pre>\n
     <\/p>\n<\/div>\n
    boost::exceptional_ptr\u662f\u4e00\u4e2a\u7c7b\u4f3c\u667a\u80fd\u6307\u9488\u7684\u4e1c\u897f, \u7528\u6765\u8de8\u7ebf\u7a0b\u8f6c\u53d1\u5f02\u5e38\u7684, \u53ef\u53c2\u8003\u6587\u732e[3].<\/p>\n
    \u7136\u540e, \u6210\u5458\u53d8\u91cf\u7684\u8bdd, \u56e0\u4e3aget_future\u6309\u8bbe\u5b9a\u53ea\u80fd\u8c03\u7528\u4e00\u6b21, \u6240\u4ee5\u6211\u4eec\u9700\u8981\u4e00\u4e2aflag\u6765\u7ef4\u6301, \u4e0b\u9762\u79f0\u5176\u4e3a\u00a0m_future_obtained\u00a0<\/span><\/code>. \u9664\u6b64\u4e4b\u5916, \u5c31\u662f\u4e00\u4e2afuture_object\u7684\u667a\u80fd\u6307\u9488\u4e86, \u4e0b\u9762\u79f0\u5176\u4e3a\u00a0m_future_entity\u00a0<\/span><\/code>. \u4e5f\u56e0\u4e3aget_future\u53ea\u80fd\u8c03\u4e00\u6b21, boost\u4e2d, future_object\u7684\u667a\u80fd\u6307\u9488\u662f\u5ef6\u8fdf\u521d\u59cb\u5316\u7684, \u6240\u4ee5boost\u7684\u5b9e\u73b0\u4e2d\u4f1a\u6709lazy_init\u8fd9\u4e2a\u79c1\u6709\u51fd\u6570. \u4f46\u662f, promise\u672c\u8eab\u6ca1\u6709\u9501, \u800c\u53e4\u8001\u7684boost 1.41\u53c8\u8fd8\u6ca1\u6709atomic\u5e93, \u6240\u4ee5\u8001\u7248\u672cboost\u7684lazy_init\u662f\u4e0d\u5b89\u5168\u7684, \u8fd9\u4e2a\u95ee\u9898\u540e\u6765\u7248\u672c\u7684boost\u7528atomic\u5e93\u89e3\u51b3, \u4f46\u6211\u4eec\u7684\u7cfb\u5217\u6587\u7ae0\u8fd8\u6ca1\u6709\u8ba8\u8bba\u5230atomic, \u6240\u4ee5\u8fd9\u91cc\u6211\u4eec\u5c31\u4e0d\u7528lazy_init\u4e86, \u76f4\u63a5\u5728\u6784\u9020\u51fd\u6570\u4e2d\u521d\u59cb\u5316future_object:<\/p>\n
    class future_already_retrieved;\r\nclass promise_already_satisfied;\r\nclass broken_promise;\r\n\r\nnamespace detail {\r\ntemplate<typename T>\r\nclass future_object;\r\n} \/\/ namespace detail\r\n\r\ntemplate<typename T>\r\nclass unique_future;\r\n\r\nclass promise {\r\nprivate:\r\n    promise(const promise& rhs); \/\/ = delete\r\n    promise& operator=(promise& rhs); \/\/ = delete\r\npublic:\r\n    promise() : m_future_entity(new detail::future_object<T>), m_future_obtained(false) {\r\n        \/\/ pass\r\n    }\r\n    ~promise() {\r\n        if (m_future_entity) {\r\n            boost::lock_guard<boost::mutex> lock(m_future_entity->mutex);\r\n\r\n            if (!m_future_entity->done) {\r\n                m_future_entity->mark_exceptional_finish_internal(\r\n                    boost::copy_exception(broken_promise()));\r\n            }\r\n        }\r\n    }\r\n\r\n    unique_future<T> get_future() {\r\n        if (m_future_obtained) {\r\n            throw future_already_retrieved();\r\n        }\r\n        m_future_obtained = true;\r\n        return unique_future<T>(m_future_entity);\r\n    }\r\n\r\n    void set_value(const T& value) {\r\n        boost::lock_guard<boost::mutex> lock(m_future_entity->mutex);\r\n        if (m_future_entity->done) {\r\n            throw promise_already_satisfied();\r\n        }\r\n        m_future_entity->mark_result_finish_internal(value);\r\n    }\r\n\r\n    void set_exception(boost::exceptional_ptr p) {\r\n        boost::lock_guard<boost::mutex> lock(m_future_entity->mutex);\r\n        if (m_future_entity->done) {\r\n            throw promise_already_satisfied();\r\n        }\r\n        m_future_entity->mark_exceptional_finish_internal(p);\r\n    }\r\n\r\nprivate:\r\n    boost::shared_ptr<detail::future_object<T> > m_future_entity;\r\n    bool m_future_obtained;\r\n};<\/pre>\n
    \u5f88\u660e\u663e\u8fd9\u91cc\u7684\u00a0get_future\u00a0<\/span><\/code>\u53ea\u80fd\u8c03\u7528\u4e00\u6b21\u7684\u8bbe\u5b9a\u4e5f\u4e0d\u662f\u7ebf\u7a0b\u5b89\u5168\u7684, \u4f1a\u51fa\u73b0\u00a0get_future<\/span>\u88ab\u6210\u529f\u8c03\u7528\u591a\u6b21\u7684\u60c5\u51b5,<\/span>\u00a0<\/span>\u4f46\u662f\u8c03\u591a\u4e86\u5176\u5b9e\u4e5f\u6ca1\u5565\u5173\u7cfb,<\/span>\u00a0<\/span>\u6bd5\u7adf<\/span>\u00a0<\/span><\/code>shared_ptr`\u7684\u590d\u5236\u662f\u7ebf\u7a0b\u5b89\u5168\u7684, \u6240\u4ee5\u76f4\u5230boost1.66, \u8fd9\u4e2a\u53ef\u80fd\u8c03\u591a\u6b21\u7684\u95ee\u9898\u4e5f\u6ca1\u89e3\u51b3.<\/p>\n
    set_value\u00a0<\/span><\/code>\u548c\u00a0set_expection\u00a0<\/span><\/code>\u90fd\u9700\u8981\u6539\u53d8\u00a0future_object\u00a0<\/span><\/code>\u7684\u72b6\u6001, \u6240\u4ee5\u9700\u8981\u5c06\u00a0future_object\u00a0<\/span><\/code>\u7684\u9501\u66b4\u9732\u51fa\u6765, \u5373m_future_entity<\/span>-><\/span>mutex\u00a0<\/span><\/code>. \u53e6\u5916,\u00a0set_value\u00a0<\/span><\/code>\u6216\u00a0set_expection\u00a0<\/span><\/code>\u53ea\u80fd\u8c03\u4e00\u6b21, \u6240\u4ee5\u00a0future_object\u00a0<\/span><\/code>\u5f97\u628aflag\u66b4\u9732\u51fa\u6765, \u5373m_future_entity<\/span>-><\/span>done<\/span>\u00a0<\/span><\/code>.<\/p>\n
    \u51e0\u4e2a\u5f02\u5e38\u4e5f\u662f\u6d3e\u751f\u81eastd::logic_error:<\/p>\n
    \n
    class future_already_retrieved : public std::logic_error {\r\npublic:\r\n    future_already_retrieved() : std::logic_error(\"Future already retrieved\") {}\r\n};\r\n\r\nclass promise_already_satisfied : public std::logic_error {\r\npublic:\r\n    promise_already_satisfied() : std::logic_error(\"Promise already satisfied\") {}\r\n};\r\n\r\nclass broken_promise : public std::logic_error {\r\npublic:\r\n    broken_promise() : std::logic_error(\"Broken promise\") {}\r\n};<\/pre>\n
     <\/p>\n<\/div>\n
    unique_future<\/h3>\n
    \u4e0b\u9762\u6211\u4eec\u770b\u00a0unique_future\u00a0<\/span><\/code>, \u987e\u540d\u601d\u4e49,\u00a0unique_future\u00a0<\/span><\/code>\u662f\u4e0d\u53ef\u590d\u5236\u7684, \u8003\u8651\u79fb\u52a8\u7684\u8bdd\u5219\u662f\u53ef\u79fb\u52a8\u7684, boost\u4e2d\u4f7f\u7528\u4e86boost<\/span>::<\/span>detail<\/span>::<\/span>thread_move_t<\/span>\u00a0<\/span><\/code>\u6765\u6a21\u4eff\u79fb\u52a8, \u65b9\u4fbf\u8d77\u89c1, \u6211\u4eec\u5c31\u7528\u590d\u5236\u6784\u9020\u51fd\u6570\u6765\u79fb\u52a8.<\/p>\n
    \u5176\u4f59\u4e3b\u8981\u63a5\u53e3\u4e3a: \u83b7\u53d6\u7ed3\u679c(\u00a0get<\/span>\u00a0<\/span><\/code>), \u7b49\u5f85(\u00a0wait\u00a0<\/span><\/code>), \u5224\u65ad\u72b6\u6001(\u00a0get_state\u00a0<\/span><\/code>,\u00a0is_ready\u00a0<\/span><\/code>,\u00a0has_exception\u00a0<\/span><\/code>,\u00a0has_value\u00a0<\/span><\/code>). \u4e8e\u662f, \u7b80\u5355\u5730, \u53ef\u4ee5\u58f0\u660e\u00a0unique_future\u00a0<\/span><\/code>\u5982\u4e0b:<\/p>\n
    \n
    template<typename T> class promise;\r\ntemplate<typename T> class shared_future;\r\n\r\ntemplate<typename T>\r\nclass unique_future {\r\n     friend class shared_future<T>;\r\n     firend class promise<T>;\r\nprivate:\r\n     unique_future(unique_future& rhs); \/\/ = delete\r\n     unique_future(boost::shared_ptr<detail::future_object<T> > future_entity)\r\n          : m_future_entity(future_entity) {}\r\npublic:\r\n     unique_future(){}\r\n     ~unique_future() {}\r\n     unique_future(const unique_future<T>& rhs) \r\n        : m_future_entity(rhs.m_future_entity) {\r\n        rhs.m_future_entity->reset();\r\n     }\r\n\r\n     T get();\r\n     bool is_ready() const;\r\n     bool has_exception() const;\r\n     bool has_value() const;\r\n     void wait() const;\r\nprivate:\r\n     boost::shared_ptr<detail::future_object<T> > m_future_entity;\r\n};<\/pre>\n
     <\/p>\n<\/div>\n
    unique_future\u00a0<\/span><\/code>\u53ea\u6709\u4e00\u4e2a\u6210\u5458\u53d8\u91cf\u00a0m_future_entity\u00a0<\/span><\/code>, \u800c\u4e14\u8fd9\u4e2a\u6210\u5458\u53d8\u91cf\u53ea\u80fd\u4ece\u00a0promise\u00a0<\/span><\/code>\u6765, \u6240\u4ee5\u63a5\u53d7\u00a0future_object\u00a0<\/span><\/code>\u7684\u6784\u9020\u51fd\u6570\u662f\u79c1\u6709\u7684,\u00a0unique_future\u00a0<\/span><\/code>\u53ea\u80fd\u4ece\u00a0promise\u00a0<\/span><\/code>\u90a3\u83b7\u53d6, \u6240\u4ee5\u9700\u8981\u58f0\u660e\u00a0promise\u00a0<\/span><\/code>\u4e3a\u53cb\u5143; \u53e6\u4e00\u65b9\u9762,\u00a0shared_future\u00a0<\/span><\/code>\u4e5f\u53ea\u80fd\u4eceunique_future\u00a0<\/span><\/code>\u6784\u9020, \u9700\u8981\u8bbf\u95ee\u00a0m_future_entity\u00a0<\/span><\/code>, \u6545\u4e5f\u4e3a\u53cb\u5143.<\/p>\n
    \u4e5f\u56e0\u4e3a\u53ea\u6709\u4e00\u4e2a\u6210\u5458\u53d8\u91cf, \u5b9e\u9645\u4e0a\u8fd9\u4e9b\u65b9\u6cd5\u7684\u5b9e\u73b0\u90fd\u59d4\u6258\u7ed9\u00a0m_future_entity\u00a0<\/span><\/code>:<\/p>\n
    class future_uninitialized : public std::logic_error {\r\npublic:\r\n    future_uninitialized() : std::logic_error(\"Future Uninitialized\") {}\r\n};\r\n\r\ntemplate<typename T>\r\nT unique_future::get() {\r\n     if (!m_future_entity) {\r\n          throw future_uninitialized();\r\n     }\r\n     return m_future_entity->get();\r\n}\r\n\r\nbool unique_future::is_ready() const {\r\n     return m_future_entity && m_future_entity->is_ready();\r\n}\r\n\r\nbool unique_future::has_exception() const {\r\n     return m_future_entity && m_future_entity->has_exception();\r\n}\r\n\r\nbool unique_future::has_value() const {\r\n     return m_future_entity && m_future_entity->has_value();\r\n}\r\n\r\nvoid unique_future::wait() const {\r\n     if (!m_future_entity) {\r\n          throw future_uninitialized();\r\n     }\r\n     m_future_entity->wait(false);\r\n}<\/pre>\n
    boost1.41\u4e2d,\u00a0shared_future\u00a0<\/span><\/code>\u4e0e\u00a0unique_future\u00a0<\/span><\/code>\u51e0\u8fd1\u76f8\u540c, \u4e0d\u540c\u7684\u662f, \u7528\u00a0unique_future\u00a0<\/span><\/code>\u6784\u9020\u00a0shared_future\u00a0<\/span><\/code>\u65f6, \u4f1a\u4f7funique_future\u00a0<\/span><\/code>\u5931\u6548(m_future_entity\u88abreset). \u6545\u800c, \u8fd9\u91cc\u4e0d\u8d58\u8ff0shared_future\u7684\u5b9e\u73b0.<\/p>\n
    future_object & future_object_base<\/h3>\n
    boost1.41\u4e2d,\u00a0future_object\u00a0<\/span><\/code>\u6d3e\u751f\u81ea\u00a0future_object_base\u00a0<\/span><\/code>,\u00a0future_object\u00a0<\/span><\/code>\u6301\u6709\u7ed3\u679c, \u800c\u00a0future_object_base\u00a0<\/span><\/code>\u5219\u6301\u6709mutex, condition_variable\u7b49\u72b6\u6001, \u4e0e\u7ed3\u679c\u7684\u7c7b\u578b\u65e0\u5173.<\/p>\n
    \n
    namespace detail {\r\nstruct future_object_base {\r\n     boost::exception_ptr excpetion;\r\n     bool done;\r\n     boost::mutex mutex;\r\n     boost::condition_variable cond;\r\n\r\n     future_object_base() : done(false) {}\r\n     virtual ~future_object_base() {}\r\n\r\n     bool is_ready();\r\n     bool has_exception();\r\n     bool has_value();\r\n     void wait(bool rethrow = true);\r\n\r\n     void mark_execptional_finish_internal(const boost::exception_ptr& e);\r\n     void mark_finished_internal();\r\nprivate:\r\n     future_object_base(const future_object_base&); \/\/ = delete\r\n     future_object_base& operator=(const future_object_base&); \/\/ = delete\r\n};\r\n\r\ntemplate<typename T>\r\nstruct future_object : public future_object_base {\r\n     boost::scoped_ptr<T> result;\r\n     \r\n     future_object() : future_object_base() {}\r\n     \r\n     void mark_result_finish_internal(const T& res);\r\n     T get();\r\n     \r\nprivate:\r\n     future_object(const future_object&); \/\/ = delete\r\n     future_object& operator=(const future_object&); \/\/ = delete\r\n};<\/pre>\n
     <\/p>\n<\/div>\n
    \u5148\u770bfuture_object\u4f1a\u7b80\u5355\u4e00\u4e9b, \u56e0\u4e3a\u6ca1\u51e0\u4e2a\u65b9\u6cd5:<\/p>\n
    \n
    void future_object::mark_result_finish_internal(const T& res) {\r\n  result.reset(new T(res));\r\n  future_object_base::mark_finished_internal();\r\n}\r\n\r\nT future_object::get() {\r\n  future_object_base::wait();\r\n  return *result;\r\n}<\/pre>\n
     <\/p>\n<\/div>\n
    future_object \u7684\u7ed3\u679c\u5b58\u5728scoped_ptr\u4e2d, set_value\u7684\u65f6\u5019\u4f1a\u590d\u5236.<\/p>\n
    mark_result_finish_internal\u00a0<\/span><\/code>\u6ca1\u6709\u52a0\u9501, \u662f\u56e0\u4e3a\u53ea\u6709\u00a0promise<\/span>::<\/span>set_value\u00a0<\/span><\/code>\u4f1a\u8c03, \u800c\u00a0promise<\/span>::<\/span>set_value\u00a0<\/span><\/code>\u662f\u9501\u4e86future_object_base<\/span>::<\/span>mutex\u00a0<\/span><\/code>\u7684, \u76f8\u5f53\u4e8e\u52a0\u597d\u9501\u624d\u8c03\u7528\u00a0mark_result_finish_internal\u00a0<\/span><\/code>. \u540c\u7406,mark_execptional_finish_internal\u00a0<\/span><\/code>\u548c\u00a0mark_finished_internal\u00a0<\/span><\/code>\u5185\u4e5f\u6ca1\u6709\u52a0\u9501.<\/p>\n
    \n
    bool future_object_base::is_ready() {\r\n  boost::unique_lock<boost::mutex> lock(mutex);\r\n  return done;\r\n}\r\nbool future_object_base::has_exception() {\r\n  boost::unique_lock<boost::mutex> lock(mutex);\r\n  return done && exception;\r\n}\r\nbool future_object_base::has_value() {\r\n  boost::unique_lock<boost::mutex> lock(mutex);\r\n  return done && !exception;\r\n}\r\nvoid future_object_base::wait(bool rethrow = true) {\r\n  boost::unique_lock<boost::mutex> lock(mutex);\r\n  while (!done) {\r\n    cond.wait(lock);\r\n  }\r\n  if (rethrow && exception) {\r\n    boost::rethrow_exception(exception);\r\n  }\r\n}\r\nvoid future_object_base::mark_exceptional_finish_internal(const boost::exception_ptr& e) {\r\n  exception = e;\r\n  mark_finished_internal();\r\n}\r\nvoid future_object_base::mark_finished_internal() {\r\n  done = true;\r\n  cond.notify_all();\r\n}<\/pre>\n
     <\/p>\n<\/div>\n
    future_object_base<\/span>::<\/span>wait\u00a0<\/span><\/code>\u662f\u6709\u53c2\u6570\u7684, \u5982\u679crethrow, \u4f1a\u91cd\u65b0\u629b\u51fa\u5176\u4fdd\u5b58\u7684\u5f02\u5e38; \u4e0a\u5c42\u8c03\u7528\u4e2d,\u00a0unique_future<\/span>::<\/span>wait\u00a0<\/span><\/code>\u662f\u4e0d\u629b\u51fa\u7684, \u800c\u00a0unique_future<\/span>::<\/span>get<\/span>\u00a0<\/span><\/code>\u662f\u629b\u51fa\u7684.<\/p>\n
    \u81f3\u6b64, \u4e00\u4e2a\u57fa\u672c\u80fd\u6eda\u7684future\/promise\u8f6e\u5b50\u5c31\u7ed9\u9020\u51fa\u6765\u4e86.<\/p>\n
    wait_for_all\/wait_for_any<\/h2>\n
    \u5047\u8bbe\u4f60\u6709\u597d\u4e9b\u4e2afuture, \u9700\u8981\u8fd9\u4e9bfuture\u5168\u90e8ready\u6216\u4efb\u610f\u4e00\u4e2afuture ready\u7684\u65f6\u5019\u7ee7\u7eed\u5f80\u4e0b\u8d70, \u4f60\u5c31\u53ef\u80fd\u9700\u8981\u00a0wait_for_all\u00a0<\/span><\/code>\u548cwait_for_any\u00a0<\/span><\/code>.\u00a0wait_for_all\u00a0<\/span><\/code>\u597d\u7406\u89e3, \u4f60\u8981\u5408\u5e76\u4e24\u4e2a\u5de5\u4f5c\u7ebf\u7a0b\u7684\u7ed3\u679c\u4ec0\u4e48\u7684.\u00a0wait_for_any\u00a0<\/span><\/code>\u7684\u8bdd, \u9700\u8981\u5bf9\u7ed3\u679c\u8fdb\u4e00\u6b65\u5904\u7406, \u5904\u7406\u8fd8\u6bd4\u8f83\u8017\u65f6\u6240\u4ee5\u9700\u8981\u6765\u4e00\u4e2a\u5904\u7406\u4e00\u4e2a? \u597d\u5427, \u5176\u5b9e\u6211\u4e5f\u6ca1\u60f3\u5230\u4ec0\u4e48\u7279\u522b\u5178\u578b\u7684\u573a\u666f.<\/p>\n
    wait_for_all\u00a0<\/span><\/code>\u7684\u5b9e\u73b0\u8fd8\u662f\u5f88\u7b80\u5355\u7684, \u4e00\u4e2a\u4e2a\u7b49\u5c31\u662f\u4e86, \u6bd4\u5982\u8bf4\u7b493\u4e2afuture\u7684\u7248\u672c:<\/p>\n
    \n
    template<typename F1, typename F2, typename F3>\r\nvoid wait_for_all(F1& f1, F2& f2, F3& f3) {\r\n     f1.wait();\r\n     f2.wait();\r\n     f3.wait();\r\n}<\/pre>\n
     <\/p>\n<\/div>\n
    \u975e\u4fb5\u5165, \u7b80\u5355\u7c97\u66b4, C++11\u548cboost.thread\u7684future\u6df7\u5408\u7740\u7b49\u5f85\u90fd\u884c. \u4e0d\u8fc7\u00a0wait_for_all\u00a0<\/span><\/code>\u66f4\u9002\u5408\u7b49\u4e00\u4e2a\u8fed\u4ee3\u5668\u533a\u95f4\u7684future\u00a0\u4e24\u4e09\u4e2afuture\u624b\u52a8wait\u4e00\u4e0b\u5c31\u597d\u4e86\u00a0<\/del>, \u8fed\u4ee3\u5668\u533a\u95f4\u6709\u4e0d\u540c\u5e93\u7684future\u6df7\u5408\u7684\u60c5\u51b5\u2026\u60f3\u5fc5\u6bd4\u8f83\u5c11\u5427\u2026<\/p>\n
    \u4f46\u662f,\u00a0wait_for_any\u00a0<\/span><\/code>\u5728\u73b0\u6709\u63a5\u53e3\u4e0b\u5c31\u6ca1\u6709\u975e\u4fb5\u5165\u7684\u5b9e\u73b0\u4e86, \u9700\u8981\u5728future\u5b9e\u73b0\u91cc\u9762\u52a0callback, waiter list\u4ec0\u4e48\u7684, \u5c31\u610f\u5473\u7740\u00a0wait_for_any<\/span><\/code>\u53ea\u80fd\u7528\u6765wait\u540c\u4e00\u5e93\u4e2d\u7684future\u4e86, \u6bd4\u5982, boost\u7684\u00a0wait_for_any\u00a0<\/span><\/code>\u53ea\u80fd\u7528\u6765\u7b49boost\u7684future,\u00a0\u597d\u5427, \u6807\u51c6\u5e93\u6ca1\u6709wait_for_any\u00a0<\/del>.<\/p>\n
    boost1.41\u5b9e\u73b0\u4e86\u00a0future_waiter\u00a0<\/span><\/code>\u53bb\u6267\u884c\u7b49\u5f85, \u800c\u00a0future_waiter\u00a0<\/span><\/code>\u505a\u7684\u4e8b\u60c5, \u5b9e\u9645\u4e0a\u662f\u5411\u00a0future_object_base\u00a0<\/span><\/code>\u6ce8\u518c\u4e86\u4e00\u4e2a\u6761\u4ef6\u53d8\u91cf,mark_finished_internal\u00a0<\/span><\/code>\u7684\u65f6\u5019\u987a\u4fbfnotify\u4e00\u4e2a\u6ce8\u518c\u8fdb\u6765\u7684\u6761\u4ef6\u53d8\u91cf. \u6709notify\u81ea\u7136\u662f\u6709future\u5b8c\u6210\u4e86, \u7136\u540e\u5c31\u8fd4\u56de\u4e2a\u6574\u6570, \u6307\u51fa\u662f\u7b2c\u51e0\u4e2afuture\u5b8c\u6210\u4e86.<\/p>\n
    \n
    template<typename F1, typename F2, typename F3>\r\nunsigned wait_for_any(F1& f1, F2& f2, F3& f3) {\r\n     detail::future_waiter waiter;\r\n     waiter.add(f1);\r\n     waiter.add(f2);\r\n     waiter.add(f3);\r\n     return waiter.wait();\r\n}<\/pre>\n
     <\/p>\n<\/div>\n
    future_waiter\u00a0<\/span><\/code>\u7684\u63a5\u53e3\u6bd4\u8f83\u5c11:<\/p>\n
    \n
    namespace detail {\r\nclass future_waiter {\r\npublic:\r\n     future_waiter() : m_future_count(0) {}\r\n     ~future_waiter();\r\npublic:\r\n     template<typename F>\r\n     void add(F& f);\r\n     unsigned wait();\r\n\r\nprivate:\r\n     boost::condition_variable_any m_cond;\r\n     std::vector<detail::registered_waiter> m_waiting_futures;\r\n     unsigned m_future_count;\r\n};\r\n} \/\/ namespace future_waiter<\/pre>\n
     <\/p>\n<\/div>\n
    \u5176\u4e2d, m_waiting_futures\u8868\u793a\u6b63\u5728\u7b49\u5f85\u7684future.<\/p>\n
    \u90a3\u4e48,\u00a0registered_waiter\u00a0<\/span><\/code>\u9700\u8981\u4ec0\u4e48\u4fdd\u5b58\u4ec0\u4e48\u4fe1\u606f\u5462? \u9996\u5148\u00a0future\u00a0<\/span><\/code>\u6216\u00a0future_object\u00a0<\/span><\/code>, \u8fd9\u91cc\u53ef\u4ee5\u7528\u00a0future_object\u00a0<\/span><\/code>\u7684\u667a\u80fd\u6307\u9488, \u76f4\u63a5\u4ecefuture\u4e2d\u62ff\u5c31\u884c; \u5176\u6b21, \u67d0\u4e2a\u6807\u8bb0, \u4ee5\u4fbf\u00a0future_waiter\u00a0<\/span><\/code>\u6790\u6784\u7684\u65f6\u5019, \u4ece\u00a0future_object_base\u00a0<\/span><\/code>\u4e2d\u6ce8\u9500, \u5982\u679c\u4e0d\u6ce8\u9500, \u5c31\u53ef\u80fd\u4f1anotify\u4e00\u4e2a\u5df2\u7ecf\u9500\u6bc1\u7684\u6761\u4ef6\u53d8\u91cf; \u6700\u540e\u5c31\u662ffuture\u7684\u987a\u5e8f\u4fe1\u606f\u4e86, \u6bd5\u7adf\u5f97\u8fd4\u56de\u662f\u7b2c\u51e0\u4e2afuture ready\u4e86:<\/p>\n
    \n
    namespace detail {\r\nstruct registered_waiter {\r\n  boost::shared_ptr<detail::future_object_base> future_entity;\r\n  detail::future_object_base::waiter_list::iterator wait_iterator;\r\n  unsigned index;\r\n\r\n  registered_waiter(\r\n      const boost::shared_ptr<detail::future_object_base>& future_entity_,\r\n      detail::future_object_base::waiter_list::iterator wait_iterator_,\r\n      unsigned index_) :\r\n    future_entity(future_entity_),\r\n    wait_iterator(wait_iterator_),\r\n    index(index_) { }\r\n};\r\n} \/\/ namespace detail<\/pre>\n
     <\/p>\n<\/div>\n
    \u8fd9\u91cc\u7528\u7684\u6807\u8bb0\u662f\u00a0future_object_base\u00a0<\/span><\/code>\u7684\u00a0waiter_list\u00a0<\/span><\/code>\u7684\u8fed\u4ee3\u5668, \u800c\u00a0waiter_list\u00a0<\/span><\/code>\u53ef\u4ee5\u662f\u4e00\u4e2acondition_variable_any\u6307\u9488\u7684list:<\/p>\n
    \n
    namespace detail {\r\nstruct future_object_base {\r\n     \/\/...\r\n     typedef std::list<boost::condition_variable_any*> waiter_list;\r\n     waiter_list external_waiters;\r\n     \/\/...\r\n};\r\n} \/\/ namespace detail<\/pre>\n
     <\/p>\n<\/div>\n
    \u8fd9\u6837\u6211\u4eec\u53bb\u5199\u00a0future_waiter<\/span>::<\/span>add\u00a0<\/span><\/code>\u51fd\u6570\u4e86:<\/p>\n
    \n
    namespace detail {\r\ntemplate<typename F>\r\nvoid future_waiter::add(F& f) {\r\n    if (f.m_future_entity) {\r\n    m_waiting_futures.push_back(\r\n        registered_waiter(f.m_future_entity,\r\n                          f.m_future_entity->register_external_waiter(&m_cond),\r\n                          m_future_count));\r\n    }\r\n    ++m_future_count;\r\n}\r\n} \/\/ namespace detail<\/pre>\n
     <\/p>\n<\/div>\n
    \u8fd9\u91cc\u9700\u8981\u8c03\u7528\u00a0future_object_base\u00a0<\/span><\/code>\u7684\u00a0register_external_waiter\u00a0<\/span><\/code>\u5c06m_cond\u7684\u6307\u9488\u6ce8\u518c\u5230\u00a0future_object_base\u00a0<\/span><\/code>\u7684external_waiters\u00a0<\/span><\/code>\u4e2d, \u5e76\u8fd4\u56de\u5176\u8fed\u4ee3\u5668, \u8fd9\u4e2a\u8fed\u4ee3\u5668\u9700\u8981\u4fdd\u8bc1\u5176\u4ed6\u5143\u7d20\u5220\u9664\u540e\u4ecd\u7136\u6709\u6548, \u6240\u4ee5\u00a0future_object_base<\/span>::<\/span>waiter_list<\/span><\/code>\u7528\u7684\u662f\u00a0std<\/span>::<\/span>list\u00a0<\/span><\/code>:<\/p>\n
    \n
    namespace detail {\r\nstruct future_object_base {\r\n  \/\/...\r\n  typedef std::list<boost::condition_variable*> waiter_list;\r\n  waiter_list external_waiters;\r\n  waiter_list::iterator register_external_waiter(boost::condition_variable_any* cv) {\r\n    boost::unique_lock<boost::mutex> lock(mutex);\r\n    return external_waiters.insert(external_waiters.end(), cv);\r\n  }\r\n  \/\/...\r\n};\r\n} \/\/ namespace detail<\/pre>\n
     <\/p>\n<\/div>\n
    \u7136\u540e\u00a0future_waiter\u00a0<\/span><\/code>\u6790\u6784\u51fd\u6570\u4e2d\u6ce8\u9500\u4e4b\u524d\u6ce8\u518c\u7684\u6761\u4ef6\u53d8\u91cf\u6307\u9488, \u5c31\u662f\u4ece\u00a0external_waiters\u00a0<\/span><\/code>\u4e2derase\u6389:<\/p>\n
    \n
    future_waiter::~future_waiter() {\r\n  for (size_t i = 0; i < m_waiting_futures.size(); ++i) {\r\n    registered_waiter& waiter = m_waiting_futures[i];\r\n    waiter.future_entity->remove_external_waiter(waiter.wait_iterator);\r\n  }\r\n}\r\n\r\nnamespace detail {\r\nstruct future_object_base {\r\n  \/\/...\r\n  typedef std::list<boost::condition_variable_any*> waiter_list;\r\n  waiter_list external_waiters;\r\n  void remove_external_waiter(waiter_list::iterator it) {\r\n    boost::lock_guard<boost::mutex> lock(mutex);\r\n    external_waiters.erase(it);\r\n  }\r\n  \/\/...\r\n};\r\n} \/\/ namespace detail<\/pre>\n
     <\/p>\n<\/div>\n
    \u5269\u4e0b\u7684\u662f\u6700\u590d\u6742\u7684\u00a0future_waiter<\/span>::<\/span>wait\u00a0<\/span><\/code>, \u4e3a\u4ec0\u4e48\u8bf4\u6700\u590d\u6742\u5462? \u56e0\u4e3a\u6211\u4eec\u628a\u00a0future_waiter<\/span>::<\/span>m_cond\u00a0<\/span><\/code>\u6ce8\u518c\u5230future_object_base\u00a0<\/span><\/code>\u53bb\u4e86, \u4e4b\u540e\u81ea\u7136\u662f\u8981wait\u8fd9\u4e2a\u00a0m_cond\u00a0<\/span><\/code>\u5bf9\u5427, \u4f46\u662f\u00a0condition_variable_any<\/span>::<\/span>wait\u00a0<\/span><\/code>\u9700\u8981\u4e00\u4e2a\u9501\u4f5c\u4e3a\u53c2\u6570\u5440! \u88abnotify\u4e4b\u540e, \u6211\u4eec\u9700\u8981\u68c0\u67e5\u00a0m_waiter_futures\u00a0<\/span><\/code>\u4e2d\u7684\u6240\u6709future, \u6240\u4ee5\u8fd9\u4e2a\u9501\u7b49\u4ef7\u4e8e\u00a0m_waiting_futures\u00a0<\/span><\/code>\u4e2d\u7684\u6240\u6709future\u7684\u9501, \u8fd9\u4e2a\u5c31\u9700\u8981\u4e00\u6b21\u9501\u4e00vector\u7684mutex\u4e14\u907f\u514d\u6b7b\u9501, \u5e78\u8fd0\u7684\u662f,\u00a0boost<\/span>::<\/span>lock<\/span>\u00a0<\/span><\/code>\u5df2\u7ecf\u63d0\u4f9b\u4e86\u8fd9\u4e2a\u8bed\u4e49. \u4e8e\u662f, \u6211\u4eec\u53ef\u4ee5\u5b9e\u73b0\u4e00\u4e2a\u7279\u522b\u7684\u9501\u7ed3\u6784all_future_entity_lock\u00a0<\/span><\/code>:<\/p>\n
    \n
    namespace detail {\r\nstruct all_future_entity_lock {\r\n     all_future_entity_lock(std::vector<detail::registered_waiter>& futures);\r\n     void lock();\r\n     void unlock();\r\n};\r\n\r\nunsigned future_waiter::wait() {\r\n    all_future_entity_lock lk(m_waiting_futures);\r\n    for (;;) {\r\n      for (size_t i = 0; i < m_waiting_futures.size(); ++i) {\r\n        detail::registered_waiter& waiter = m_waiting_futures[i];\r\n        if (waiter.future_entity->done) {\r\n          return waiter.index;\r\n        }\r\n      }\r\n      m_cond.wait(lk);\r\n    }\r\n}\r\n} \/\/ namespace detail<\/pre>\n
     <\/p>\n<\/div>\n
    \u7531\u4e8e\u00a0boost<\/span>::<\/span>lock<\/span>\u00a0<\/span><\/code>\u51fd\u6570\u63a5\u53d7\u7684\u662f\u53ef\u9501\u5bf9\u8c61, \u6211\u4eec\u6ca1\u6cd5\u5f04\u4e00\u4e2amutex\u6307\u9488\u7684\u5bb9\u5668\u4f20\u5230\u00a0boost<\/span>::<\/span>lock<\/span>\u00a0<\/span><\/code>\u53bb, \u6240\u4ee5\u6211\u4eec\u5f97\u6784\u9020\u522b\u7684\u53ef\u9501\u5bf9\u8c61\u7684\u5bb9\u5668,boost<\/span>::<\/span>unique_lock\u00a0<\/span><\/code>\u56e0\u4e3a\u5176\u5141\u8bb8\u5ef6\u8fdf\u9501\u5b9a\u7684\u7279\u6027\u6b63\u597d\u7b26\u5408\u6211\u4eec\u7684\u9700\u6c42:<\/p>\n
    \n
    namespace detail {\r\nstruct all_future_entity_lock {\r\n  unsigned count;\r\n  boost::scoped_array<boost::unique_lock<boost::mutex> > locks;\r\n\r\n  all_future_entity_lock(std::vector<detail::registered_waiter>& futures) :\r\n    count(futures.size()), locks(new boost::unique_lock<boost::mutex>[futures.size()]) {\r\n    for (size_t i = 0; i < count; ++i) {\r\n      locks[i] = boost::unique_lock<boost::mutex>(futures[i].future_entity->mutex, boost::defer_lock);\r\n    }\r\n    lock();\r\n  }\r\n  void lock() {\r\n    boost::lock(locks.get(), locks.get() + count);\r\n  }\r\n  void unlock() {\r\n    for (unsigned i = 0; i< count; ++i) {\r\n      locks[i].unlock();\r\n    }\r\n  }\r\n};\r\n} \/\/ namespace detail<\/pre>\n
     <\/p>\n<\/div>\n
    \u6784\u9020\u00a0boost<\/span>::<\/span>unique_lock\u00a0<\/span><\/code>\u7684\u65f6\u5019,\u00a0boost<\/span>::<\/span>defer_lock\u00a0<\/span><\/code>\u8fd9\u4e2a\u53c2\u6570\u662f\u9700\u8981\u7684, \u5426\u5219\u6784\u9020\u7684\u65f6\u5019\u5c31\u4f1a\u9501\u5b9a, \u53ef\u80fd\u9020\u6210\u6b7b\u9501. \u53e6\u5916\u8fd9\u91cc\u7528scoped_array\u7684\u539f\u56e0\u5176\u5b9e\u7b14\u8005\u4e5f\u4e0d\u77e5\u9053, \u6309\u8bf4\u7528vector\u4e5f\u5e94\u8be5\u53ef\u4ee5, vector\u4e0escoped_array\u4e0d\u540c\u7684\u4e5f\u8bb8\u5c31\u662fscoped_array\u662f\u4e0d\u53ef\u590d\u5236\u7684, \u4e5f\u8bb8\u662f\u4e3a\u4e86\u4fdd\u8bc1\u4e0d\u53ef\u590d\u5236?<\/p>\n
    \u53e6\u5916, \u56e0\u4e3a\u00a0boost<\/span>::<\/span>condition_variable<\/span>::<\/span>wait\u00a0<\/span><\/code>\u53ea\u63a5\u53d7boost\u5185\u5b9a\u4e49\u7684\u9501, \u5982\u679c\u60f3\u63a5\u53d7\u4efb\u610f\u7c7b\u578b\u7684\u9501, \u5f97\u7528boost<\/span>::<\/span>condition_variable_any\u00a0<\/span><\/code>.<\/p>\n
    \u6700\u540e, \u6211\u4eec\u9700\u8981\u4fee\u6539\u4e00\u4e0b\u00a0future_object_base<\/span>::<\/span>mark_finished_internal\u00a0<\/span><\/code>:<\/p>\n
    \n
    namespace detail {\r\n\r\nvoid mark_finished_internal() {\r\n    done = true;\r\n    cond.notify_all();\r\n    for (waiter_list::const_iterator it = external_waiters.begin();\r\n      it != external_waiters.end();\r\n      ++it) {\r\n      (*it)->notify_all();\r\n    }\r\n}\r\n\r\n} \/\/ namespace detail<\/pre>\n
     <\/p>\n<\/div>\n
    \u7efc\u5408\u4e0a\u8ff0\u4ee3\u7801, \u6211\u4eec\u7684\u00a0wait_for_any\u00a0<\/span><\/code>\u5e94\u8be5\u5c31\u5b8c\u6210\u4e86, \u5b83\u80fd\u5426\u4fdd\u8bc1\u5f97\u5230\u7b2c\u4e00\u4e2aready\u7684future\u7684\u5462?<\/p>\n
    \u9996\u5148,\u00a0future_waiter<\/span>::<\/span>wait\u00a0<\/span><\/code>\u4e2d, \u5982\u679c\u6709\u591a\u4e8e\u4e00\u4e2afuture\u5df2\u7ecfready\u4e86, \u90a3\u8fd4\u56de\u7684\u5176\u5b9e\u4e0d\u662f\u7b2c\u4e00\u4e2aready\u7684, \u56e0\u4e3a\u8c01\u662f\u7b2c\u4e00\u4e2aready\u8fd9\u4e2a\u4fe1\u53f7\u5df2\u7ecf\u4e22\u5931\u4e86.<\/p>\n
    \u5982\u679c\u8d70\u5230\u00a0m_cond<\/span>.<\/span>wait<\/span>(<\/span>lk<\/span>)<\/span>\u00a0<\/span><\/code>\u7684\u65f6\u5019\u4ecd\u6ca1\u6709future\u662fready\u7684, \u4e5f\u5c31\u662f, \u8be5\u7ebf\u7a0b\u662f\u6302\u8d77\u540e\u88ab\u5524\u9192\u7684\u60c5\u51b5, \u6bd4\u5982, \u4e24\u4e2a\u7ebf\u7a0bt1\u548ct2\u5728\u5f88\u76f8\u8fd1\u7684\u65f6\u95f4notify\u540c\u4e00\u4e2acondition_variable:<\/p>\n
    t1 notify\u4e86\u4e4b\u540e, \u56e0\u4e3a\u8fd8\u6ca1\u6709\u89e3\u9501, wait_for_any\u88ab\u5524\u9192\u540e\u91cd\u65b0\u83b7\u5f97\u9501\u7684\u8fc7\u7a0b\u8fd8\u5728\u963b\u585e, \u4f46\u8fd9\u65f6,\u00a0t2\u00a0<\/span><\/code>\u7684promise\u7684future\u7684\u9501\u53ef\u80fd\u6ca1\u8c01\u5360\u6709, \u8fd9\u5c31\u4f7f\u5f97\u00a0t2\u00a0<\/span><\/code>\u53ef\u4ee5\u00a0set_value\u00a0<\/span><\/code>, \u4e8e\u662f\u53c8\u89e6\u53d1\u4e86\u4e00\u6b21notify, \u7136\u800c, \u56e0\u4e3acondition_variable\u5185\u90e8\u72b6\u6001\u662f\u6709\u9501\u4fdd\u62a4\u7684, \u6240\u4ee5\u8fd9\u6b21notify\u662f\u53ef\u4ee5\u5b8c\u6210\u7684, \u867d\u7136\u6ca1\u6709\u7ebf\u7a0b\u88ab\u5524\u9192. \u4e8e\u662f\u4e4e,\u00a0t2\u00a0<\/span><\/code>\u7684promise\u7684future\u88ab\u00a0mark_finished_internal\u00a0<\/span><\/code>, \u89e3\u4e86\u81ea\u5df1\u7684\u9501. \u518d\u7136\u540e,\u00a0t1\u00a0<\/span><\/code>\u53ef\u80fd\u73b0\u5728\u624d\u89e3\u9501,wait_for_any\u00a0<\/span><\/code>\u624d\u91cd\u65b0\u6240\u6709\u9501, \u8fd9\u65f6\u53bb\u904d\u5386\u00a0future\u00a0<\/span><\/code>, \u4f1a\u53d1\u73b0\u6709\u4e24\u4e2a\u90fdready\u4e86.<\/p>\n
    \u867d\u7136\u00a0wait_for_any\u00a0<\/span><\/code>\u4e0d\u80fd\u4fdd\u8bc1\u5f97\u5230\u7684\u662f\u7b2c\u4e00\u4e2aready\u7684\u00a0future\u00a0<\/span><\/code>, \u4f46\u662f,\u00a0wait_for_any\u00a0<\/span><\/code>\u7ed3\u675f\u7684\u65f6\u5019, \u53ef\u4ee5\u4fdd\u8bc1\u81f3\u5c11\u4e00\u4e2afuture\u662fready\u7684.<\/p>\n
    \u53e6\u5916, \u4ece\u5b9e\u73b0\u53ef\u4ee5\u770b\u51fa, \u5c06\u540c\u4e00\u00a0future\u00a0<\/span><\/code>\u7684\u4e24\u4e2a\u00a0shared_future\u00a0<\/span><\/code>\u4f20\u5230\u00a0wait_for_any\u00a0<\/span><\/code>\u662f\u8981\u6b7b\u9501\u7684, \u56e0\u4e3a\u00a0all_future_entity_lock\u00a0<\/span><\/code>\u4e2d\u5e76\u6ca1\u6709\u6392\u91cd,\u00a0\u5b9e\u73b0\u6392\u91cd\u7684wait_for_any\u7559\u4f5c\u4f5c\u4e1a\u00a0<\/del>.<\/p>\n
    \u603b\u7ed3<\/h2>\n
    \u4e0a\u9762\u6211\u4eec\u5206\u6790\u4e86boost1.41\u4e2d\u00a0future<\/span>\/<\/span>promise\u00a0<\/span><\/code>\u7684\u4e3b\u7ebf\u4ee3\u7801, \u5f53\u7136, \u8fd8\u6709\u4e00\u4e9b\u529f\u80fd\u6ca1\u6709\u5206\u6790, \u6bd4\u5982\u00a0packaged_task\u00a0<\/span><\/code>.<\/p>\n
    \u6587\u7ae0\u5f00\u59cb\u7684\u65f6\u5019\u6211\u4eec\u8bf4\u9053,\u00a0promise\u00a0<\/span><\/code>\u4e5f\u6ca1\u795e\u5947\u5230\u53ef\u4ee5\u5e2e\u4f60\u6355\u83b7\u5f02\u5e38, \u4f46\u662f\u5982\u679c\u6211\u7684\u7ebf\u7a0b\u53ea\u9700\u8981\u63d0\u4f9b\u4e00\u4e2a\u7ed3\u679c, \u4e5f\u5c31\u662f\u8bf4\u6211\u5c31\u60f3\u8d77\u4e2a\u7ebf\u7a0b\u8dd1\u4e2a\u6709\u5355\u4e00\u8fd4\u56de\u503c\u7684\u51fd\u6570, boost\u63d0\u4f9b\u4e86\u00a0packaged_task\u00a0<\/span><\/code>:<\/p>\n
    \n
    int calculate_the_answer_to_life_the_universe_and_everything() {\r\n    return 42;\r\n}\r\n\r\nint main() {\r\n     boost::packaged_task<int> task(calculate_the_answer_to_life_the_universe_and_everything);\r\n     boost::future<int> f = task.get_future();\r\n     boost::thread tr1(boost::move(task));\r\n     \/\/ do something\r\n     assert(f.get() == 42);\r\n     \/\/ do something else\r\n     tr1.join();\r\n     return 0;\r\n}<\/pre>\n
     <\/p>\n<\/div>\n
    \u5982\u679c\u7406\u89e3\u4e86\u00a0future<\/span>\/<\/span>promise\u00a0<\/span><\/code>\u7684\u5b9e\u73b0,\u00a0packaged_task\u00a0<\/span><\/code>\u7684\u5b9e\u73b0\u4e5f\u5f88\u597d\u7406\u89e3, \u8fd9\u91cc\u5c31\u4e0d\u8d58\u8ff0\u4e86.<\/p>\n
    \u81f3\u4e8e\u8bf4\u00a0packaged_task\u00a0<\/span><\/code>\u548c\u00a0thread\u00a0<\/span><\/code>\u90fd\u4e0d\u60f3\u7528, \u60f3\u8981\u66f4\u7b80\u6d01\u7684, boost1.52\u540e\u4e5f\u63d0\u4f9b\u4e86\u00a0boost<\/span>::<\/span>async\u00a0<\/span><\/code>, \u4e0d\u8fc71.52\u90fd2012\u5e74\u672b\u4e86,std<\/span>::<\/span>async\u00a0<\/span><\/code>\u4e5f\u65e9\u5df2\u7ecf\u8fdb\u5165C++11\u6807\u51c6.<\/p>\n
    async\u7684\u5b9e\u73b0\u590d\u6742\u4e00\u4e9b, \u4e00\u65b9\u9762\u9700\u8981\u8003\u8651launch policy, \u53e6\u4e00\u65b9\u9762, \u9700\u8003\u8651\u7528\u7ebf\u7a0b\u6c60\u8fd8\u662f\u8bf4\u603b\u662f\u8d77\u65b0\u7ebf\u7a0b\u7b49\u7b49, \u4f46\u8003\u8651\u7b80\u5355\u7c97\u66b4\u7684\u5b9e\u73b0\u8bdd, \u53ef\u4ee5\u662f\u5bf9\u00a0packaged_task\u00a0<\/span><\/code>\u7684\u5c01\u88c5.<\/p>\n
    boost1.54\u540e, \u52a0\u5165\u4e86\u00a0future<\/span>::<\/span>then<\/span>\u00a0<\/span><\/code>, \u4ee5\u63d0\u4f9bfuture\u95f4\u7684\u4e32\u8054\u64cd\u4f5c:<\/p>\n
    \n
    int main() {\r\n     boost::future<int> f1 = boost::async([](){return 42;});\r\n     boost::future<std::string> f2 = f1.then([](boost::future<int> f) {\r\n          return boost::str(boost::format(\"%d\") % f.get()); \/\/ \u8fd9\u91cc\u4e0d\u4f1a\u963b\u585e\r\n     });\r\n     assert(\"42\" == f2.get());\r\n     return 0;\r\n}<\/pre>\n
     <\/p>\n<\/div>\n
    \u800c\u5728\u4f7f\u7528then\u7684\u573a\u5408\u4e0b,\u00a0wait_for_any\u00a0<\/span><\/code>\u7684\u963b\u585e\u7b49\u5f85\u5c31\u4e0d\u5408\u9002\u4e86, \u4e8e\u662fboost1.56\u52a0\u5165\u4e86\u00a0when_all<\/span>\/<\/span>when_any\u00a0<\/span><\/code>, \u4e0e\u00a0wait_for_any\u00a0<\/span><\/code>\u4e0d\u540c,when_any\u00a0<\/span><\/code>\u662f\u7acb\u5373\u8fd4\u56de\u53e6\u4e00\u4e2a\u00a0future\u00a0<\/span><\/code>, \u8fd9\u4f7f\u5f97\u6211\u4eec\u5728then\u4e32\u8054\u4e2d\u53ef\u4ee5\u8fbe\u5230\u7c7b\u4f3c\u00a0wait_for_any\u00a0<\/span><\/code>\u7684\u6548\u679c, \u4f46\u5374\u662f\u975e\u963b\u585e\u7684:<\/p>\n
    \n
    int main() {\r\n     boost::future<int> f1 = boost::async([]() { return 42;});\r\n     boost::future<int> f2 = boost::async([]() { return 233;});\r\n     auto f3 = boost::when_any(f1, f2);\r\n     auto f4 = f3.then([](auto& f) {\r\n          f.get();\r\n          return 1234;\r\n     });\r\n     assert(1234 == f4.get()); \/\/ \u5230\u8fd9\u91cc\u624d\u963b\u585e<\/pre>\n
     <\/p>\n<\/div>\n
    boost1.56\u7684\u53d1\u5e03\u65f6\u95f4\u867d\u7136\u53ea\u662f\u6765\u52302015\u5e74\u540e\u534a, \u7136\u800cthen\/when_any\u5e76\u6ca1\u6709\u8fdb\u5165C++17\u00a0C++17\u6bdb\u90fd\u6ca1\u6709!C++\u65e5\u5e38\u836f\u4e38!\u00a0<\/del>. \u4e0d\u8fc7\u4ece\u53c2\u8003\u6587\u732e[2]\u53ef\u4ee5\u770b\u51fa, \u4ee5\u540e\u5e94\u8be5\u662f\u5f88\u6709\u5e0c\u671b\u8fdb\u6807\u51c6\u7684.<\/p>\n
    \u81f3\u4e8easync, then, when_any\/when_all\u7684\u5b9e\u73b0, \u9700\u8981\u4e00\u4e9b\u7bc7\u5e45, \u6211\u4eec\u8fd8\u662f\u53e6\u5f00\u4e00\u7bc7\u535a\u5ba2\u518d\u53d9\u5427\u00a0\u6b64\u5751\u6709\u7f18\u518d\u586b\u7cfb\u5217\u00a0<\/del>~<\/p>\n
    Reference:<\/strong><\/p>\n