[{"_1":2,"_3":-5,"_4":-5},"loaderData",{"_5":6,"_7":8},"actionData","errors","root",{"_11":-5},"routes/user.$name.topics",{"_9":10,"_11":12,"_13":14,"_15":16,"_17":18,"_19":16},"topics",[33],"user",{"_20":21,"_13":14,"_22":23,"_24":14,"_25":26,"_27":28,"_29":16,"_30":16,"_31":32},"loginname","hunjixin","page",1,"limit",20,"total","id","32717","avatar_url","https://avatars2.githubusercontent.com/u/13759392?v=4","githubUsername","create_at","2018-04-05 15:35:51.391","score",10,"topic_count","reply_count","is_star",false,{"_20":34,"_35":21,"_36":37,"_38":39,"_40":41,"_42":43,"_44":32,"_45":32,"_30":16,"_46":47,"_25":48,"_49":50},"32124","author_id","tab","share","content","# 环境准备\r\n**工具**： git/cmake/vscode（安装js和C++插件）/python\r\n\r\n**vscode** :https://code.visualstudio.com/Download\r\n\r\n**编译参考**：https://github.com/nodejs/node/blob/master/BUILDING.md\r\n\r\n需要注意的是为了调试方便，需要在make命令中开启debug，如果觉得编译过程慢也可以适当调大并发数。\r\n```\r\n make -d j4\r\n```\r\n**命令行**：在根目录输入：\r\n```\r\n gdb node // 调试目标文件\r\n break main // 在main里加断点\r\n run test.js // 开始执行调试\r\n```\r\n**vscode**：编译完成后用vscode打开，配置编译项目，这里给出我的launch文件做参考\r\n```\r\n {\r\n \"version\": \"0.2.0\",\r\n \"configurations\": [\r\n {\r\n \"type\": \"node\",\r\n \"request\": \"launch\",\r\n \"name\": \"Launch Program\",\r\n \"program\": \"${workspaceFolder}/test.js\"\r\n },\r\n {\r\n \"name\": \"(gdb) Launch\",\r\n \"type\": \"cppdbg\",\r\n \"request\": \"launch\",\r\n \"program\": \"${workspaceRoot}/out/Debug/node\",\r\n \"args\": [\r\n \"test.js\"\r\n ],\r\n \"stopAtEntry\": true,\r\n \"cwd\": \"${workspaceRoot}\",\r\n \"environment\": [\r\n\r\n ],\r\n \"externalConsole\": true,\r\n \"MIMode\": \"gdb\",\r\n \"setupCommands\": [\r\n {\r\n \"description\": \"Enable pretty-printing for gdb\",\r\n \"text\": \"-enable-pretty-printing\",\r\n \"ignoreFailures\": true\r\n }\r\n ]\r\n }\r\n ]\r\n }\r\n```\r\n# 代码分析\r\n## setTimeout/setInterval\r\n**源码位置**：node-master/lib/timers.js\r\n - setTimeout调用过程：\r\n`setTimeout -> createSingleTimeout -> new Timeout() -> active`\r\n\r\n - setInterval调用过程：\r\n`setInterval -> createRepeatTimeout -> new Timeout -> active`\r\n\r\n两者最终都是使用的TimeOut对象，其区别在于repeat参数，这个参数控制当前timer是否重用。\r\n```js\r\n\t repeat *= 1; // coalesce to number or NaN\r\n\t if (!(repeat >= 1 && repeat <= TIMEOUT_MAX))\r\n\t\trepeat = 1; // schedule on next tick, follows browser behavior\r\n\t\r\n\t var timer = new Timeout(repeat, callback, args);\r\n\t timer._repeat = repeat;\r\n\t if (process.domain)\r\n\t\ttimer.domain = process.domain;\r\n\t\r\n\t active(timer);\r\n\t\r\n\t return timer;\r\n```\r\n\r\nactive操作会将当前的timer合并到原来的lists对象上面，这个对象按照timeout的时间分组，key为过期时间，value为一个list，存放计时器对象。\r\n\r\n```\r\n\tfunction insert(item, unrefed) {\r\n\t\r\n\t //..................\r\n\t\r\n\t // Use an existing list if there is one, otherwise we need to make a new one.\r\n\t var list = lists[msecs];\r\n\t if (!list) {\r\n\t\tdebug('no %d list was found in insert, creating a new one', msecs);\r\n\t\tlists[msecs] = list = createTimersList(msecs, unrefed);\r\n\t }\r\n\t\r\n\t //..................\r\n\t\r\n\t L.append(list, item);\r\n\t assert(!L.isEmpty(list)); // list is not empty\r\n\t}\r\n```\r\n\t\r\n计数器触发时会遍历对应list，逐个执行。调用过程：\r\n`listOnTimeout -> tryOnTimeout -> ontimeout`\r\n\t\r\n```\r\n\tfunction listOnTimeout() {\r\n\t var list = this._list;\r\n\t var msecs = list.msecs;\r\n\t\r\n\t //...........................\r\n\t\r\n\t while (timer = L.peek(list)) {\r\n\t \r\n\t //...........................\r\n\t\r\n\t\ttryOnTimeout(timer, list);\r\n\t\r\n\t }\r\n\t\r\n\t // If `L.peek(list)` returned nothing, the list was either empty or we have\r\n\t // called all of the timer timeouts.\r\n\t // As such, we can remove the list and clean up the TimerWrap C++ handle.\r\n\t debug('%d list empty', msecs);\r\n\t assert(L.isEmpty(list));\r\n\t\r\n\t // Either refedLists[msecs] or unrefedLists[msecs] may have been removed and\r\n\t // recreated since the reference to `list` was created. Make sure they're\r\n\t // the same instance of the list before destroying.\r\n\t if (list._unrefed === true && list === unrefedLists[msecs]) {\r\n\t\tdelete unrefedLists[msecs];\r\n\t } else if (list === refedLists[msecs]) {\r\n\t\tdelete refedLists[msecs];\r\n\t }\r\n\t\r\n\t // Do not close the underlying handle if its ownership has changed\r\n\t // (e.g it was unrefed in its callback).\r\n\t if (this.owner)\r\n\t\treturn;\r\n\t\r\n\t this.close();\r\n\t}\r\n```\r\n## setImmediate\r\n**setImmediate则是个简单的链表**\r\n```\r\n function Immediate() {\r\n // assigning the callback here can cause optimize/deoptimize thrashing\r\n // so have caller annotate the object (node v6.0.0, v8 5.0.71.35)\r\n this._idleNext = null;\r\n this._idlePrev = null;\r\n this._callback = null;\r\n this._argv = null;\r\n this._onImmediate = null;\r\n this._destroyed = false;\r\n this.domain = process.domain;\r\n this[async_id_symbol] = ++async_uid_fields[kAsyncUidCntr];\r\n this[trigger_id_symbol] = initTriggerId();\r\n if (async_hook_fields[kInit] > 0)\r\n emitInit(this[async_id_symbol], 'Immediate', this[trigger_id_symbol], this);\r\n }\r\n```\r\nsetImmediate函数的调用过程：\r\n`setImmediate -> createImmediate -> immediateQueue.append(immediate);`\r\n\r\n触发时执行过程：\r\n`processImmediate -> tryOnImmediate -> runCallback`\r\n\r\n```\r\n function processImmediate() {\r\n var immediate = immediateQueue.head;\r\n var tail = immediateQueue.tail;\r\n var domain;\r\n\r\n // Clear the linked list early in case new `setImmediate()` calls occur while\r\n // immediate callbacks are executed\r\n immediateQueue.head = immediateQueue.tail = null;\r\n\r\n while (immediate) {\r\n\r\n //..........................\r\n\r\n immediate._callback = immediate._onImmediate;\r\n\r\n // Save next in case `clearImmediate(immediate)` is called from callback\r\n var next = immediate._idleNext;\r\n\r\n tryOnImmediate(immediate, tail);\r\n\r\n //..........................\r\n\r\n if (immediate._idleNext)\r\n immediate = immediate._idleNext;\r\n else\r\n immediate = next;\r\n }\r\n }\r\n```\r\n## process.NextTick\r\n**源码位置**：node-master/lib/internal/process/next_tick.js\r\nprocess.NextTick实现为一个队列，nextTick函数做的工作就是把回调函数转换成TickObject，然后进到nextTickQueue队列里面。\r\n\r\n```\r\n function nextTick(callback) {\r\n\t\tif (typeof callback !== 'function')\r\n\t\t throw new errors.TypeError('ERR_INVALID_CALLBACK');\r\n\r\n\t\tif (process._exiting)\r\n\t\t return;\r\n\r\n\t\tvar args;\r\n\t\tswitch (arguments.length) {\r\n\t\t case 1: break;\r\n\t\t case 2: args = [arguments[1]]; break;\r\n\t\t case 3: args = [arguments[1], arguments[2]]; break;\r\n\t\t case 4: args = [arguments[1], arguments[2], arguments[3]]; break;\r\n\t\t default:\r\n\t\t\targs = new Array(arguments.length - 1);\r\n\t\t\tfor (var i = 1; i < arguments.length; i++)\r\n\t\t\t args[i - 1] = arguments[i];\r\n\t\t}\r\n\r\n\t\tconst asyncId = ++async_uid_fields[kAsyncUidCntr];\r\n\t\tconst triggerAsyncId = initTriggerId();\r\n\t\tconst obj = new TickObject(callback, args, asyncId, triggerAsyncId);\r\n\t\tnextTickQueue.push(obj);\r\n\t\t++tickInfo[kLength];\r\n\t\tif (async_hook_fields[kInit] > 0)\r\n\t\t emitInit(asyncId, 'TickObject', triggerAsyncId, obj);\r\n\t }\r\n```\r\n\r\nnextTick触发时的调用过程：\r\n\r\n`_tickCallback(_tickDomainCallback) -> _combinedTickCallback`\r\n\r\n其中TickInfo类型用于控制每次执行callbck（可以想象成数组上有个指向两端的指针0指向头，1指向尾）\r\n\r\n**执行nextTick回调函数**\r\n\r\n```\r\n\t function _tickDomainCallback() {\r\n\t\tdo {\r\n\t\t while (tickInfo[kIndex] < tickInfo[kLength]) {\r\n\t\t\t++tickInfo[kIndex];\r\n\t\t\tconst tock = nextTickQueue.shift();\r\n\t\t\tconst callback = tock.callback;\r\n\t\t\tconst domain = tock.domain;\r\n\t\t\tconst args = tock.args;\r\n\t\t\tif (domain)\r\n\t\t\t domain.enter();\r\n\r\n\t\t\t// CHECK(Number.isSafeInteger(tock[async_id_symbol]))\r\n\t\t\t// CHECK(tock[async_id_symbol] > 0)\r\n\t\t\t// CHECK(Number.isSafeInteger(tock[trigger_id_symbol]))\r\n\t\t\t// CHECK(tock[trigger_id_symbol] > 0)\r\n\r\n\t\t\temitBefore(tock[async_id_symbol], tock[trigger_id_symbol]);\r\n\t\t\t// TODO(trevnorris): See comment in _tickCallback() as to why this\r\n\t\t\t// isn't a good solution.\r\n\t\t\tif (async_hook_fields[kDestroy] > 0)\r\n\t\t\t emitDestroy(tock[async_id_symbol]);\r\n\r\n\t\t\t// Using separate callback execution functions allows direct\r\n\t\t\t// callback invocation with small numbers of arguments to avoid the\r\n\t\t\t// performance hit associated with using `fn.apply()`\r\n\t\t\t_combinedTickCallback(args, callback); //执行tick回调\r\n\r\n\t\t\temitAfter(tock[async_id_symbol]);\r\n\r\n\t\t\tif (kMaxCallbacksPerLoop < tickInfo[kIndex])\r\n\t\t\t tickDone();\r\n\t\t\tif (domain)\r\n\t\t\t domain.exit();\r\n\t\t }\r\n\t\t tickDone();\r\n\t\t _runMicrotasks();\r\n\t\t emitPendingUnhandledRejections();\r\n\t\t} while (tickInfo[kLength] !== 0);\r\n\t }\r\n```\r\n\r\n## EventLoop\r\nEvent Loop 简单说就是在主程序里面轮循多个队列，取出其中的回调函数并且执行，再这个过程中实现异步，同时也通过精巧的设计平衡不同类型的任务。使得程序能够尽量无阻塞的运行下去。\r\n代码如下：\r\n\r\n```\r\n int uv_run(uv_loop_t* loop, uv_run_mode mode) {\r\n int timeout;\r\n int r;\r\n int ran_pending;\r\n\r\n r = uv__loop_alive(loop);\r\n if (!r)\r\n uv__update_time(loop);\r\n\r\n while (r != 0 && loop->stop_flag == 0) {\r\n uv__update_time(loop);\r\n uv__run_timers(loop);\r\n ran_pending = uv__run_pending(loop);\r\n uv__run_idle(loop);\r\n uv__run_prepare(loop);\r\n\r\n timeout = 0;\r\n if ((mode == UV_RUN_ONCE && !ran_pending) || mode == UV_RUN_DEFAULT)\r\n timeout = uv_backend_timeout(loop);\r\n\r\n uv__io_poll(loop, timeout);//process.nextTick 和 microtask Promise\r\n uv__run_check(loop);\r\n uv__run_closing_handles(loop);\r\n\r\n if (mode == UV_RUN_ONCE) {\r\n /* UV_RUN_ONCE implies forward progress: at least one callback must have\r\n * been invoked when it returns. uv__io_poll() can return without doing\r\n * I/O (meaning: no callbacks) when its timeout expires - which means we\r\n * have pending timers that satisfy the forward progress constraint.\r\n *\r\n * UV_RUN_NOWAIT makes no guarantees about progress so it's omitted from\r\n * the check.\r\n */\r\n uv__update_time(loop);\r\n uv__run_timers(loop);\r\n }\r\n\r\n r = uv__loop_alive(loop);\r\n if (mode == UV_RUN_ONCE || mode == UV_RUN_NOWAIT)\r\n break;\r\n }\r\n```\r\n\r\n这里只分析几个相关的过程。 uv__run_timers/uv__run_check\r\n### timer对象关联\r\n\r\n`uv__run_timers -> OnTimeout -> AsyncWrap::MakeCallback`\r\n\r\nJS 在索引kOnTimeout位置挂上脚本函数listOnTimeout\r\n\r\n```\r\n function createTimersList(msecs, unrefed) {\r\n // Make a new linked list of timers, and create a TimerWrap to schedule\r\n // processing for the list.\r\n const list = new TimersList(msecs, unrefed);\r\n L.init(list);\r\n list._timer._list = list;\r\n \r\n if (unrefed === true) list._timer.unref();\r\n list._timer.start(msecs);\r\n \r\n list._timer[kOnTimeout] = listOnTimeout;\r\n \r\n return list;\r\n }\r\n```\r\n\r\nAsyncWrap::MakeCallback中object()->Get语句会获取脚本函数listOnTimeout，index参数值设置的是常量0和JS中的kOnTimeout保持一致\r\n\r\n```\r\n v8::Local cb_v = object()->Get(index);\r\n CHECK(cb_v->IsFunction());\r\n return listOnTimeoutMakeCallback(cb_v.As(), argc, argv);\r\n```\r\n\r\nuv__run_timers执行时检查是否触发时间，如果时间到了，调用listOnTimeout脚本函数执行回调函数\r\n\r\n### immediate对象关联\r\n\r\n`uv__run_check -> CheckImmediate -> MakeCallback（node.cc）`\r\n\r\n\r\nJS中\r\n\r\n```\r\n function createImmediate(args, callback) {\r\n // declaring it `const immediate` causes v6.0.0 to deoptimize this function\r\n var immediate = new Immediate();\r\n immediate._callback = callback;\r\n immediate._argv = args;\r\n immediate._onImmediate = callback;\r\n\r\n if (!process._needImmediateCallback) {\r\n process._needImmediateCallback = true; //这里在process中设置一些函数状态\r\n process._immediateCallback = processImmediate; //在c中会在进行对应\r\n }\r\n\r\n immediateQueue.append(immediate);\r\n\r\n return immediate;\r\n }\r\n```\r\n\r\n`uv__run_check->CheckImmediate->MakeCallback(node.cc)`\r\n\r\n\r\n```\r\n static void CheckImmediate(uv_check_t* handle) {\r\n Environment* env = Environment::from_immediate_check_handle(handle);\r\n HandleScope scope(env->isolate());\r\n Context::Scope context_scope(env->context());\r\n MakeCallback(env->isolate(),\r\n env->process_object(),\r\n env->immediate_callback_string(),\r\n 0,\r\n nullptr,\r\n {0, 0}).ToLocalChecked();\r\n }\r\n```\r\n\r\nuv__run_check调用CheckImmediate，最终调用MakeCallback执行processImmediate脚本函数\r\n\r\n### processNextTick对象关联\r\nJS中\r\n\r\n```\r\n // Used to run V8's micro task queue.\r\n var _runMicrotasks = {};\r\n\r\n // *Must* match Environment::TickInfo::Fields in src/env.h.\r\n var kIndex = 0;\r\n var kLength = 1;\r\n\r\n process.nextTick = nextTick;\r\n // Needs to be accessible from beyond this scope.\r\n process._tickCallback = _tickCallback;\r\n process._tickDomainCallback = _tickDomainCallback;\r\n```\r\n\r\n C中tick_callback_function函数设置到env上\r\n\r\n```\r\n Local