(evented)
a model of I/O
+
(JavaScript)
a language that was well suited to the style of programming
=
Node.js
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浏览器的影⼦子
• v8 “上下⽂文”的设计：each window and iframe in a
browser can have its own fresh JavaScript
environment. [提问 node]
• v8 限制堆的⼤大⼩小，浏览器不太可能⽤用⼤大量量内存
• node::Buffer (跳过 V8的内存分配，堆外内存）
与 v8::Uint8Array / TypedArray 的故事
• CESU-8 encoding
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C++ 11
(env.cc)
auto close_and_finish = [](Environment* env,
uv_handle_t* handle, void* arg) {
…
}
“隔离区”
• class v8::Isolate {}
• An isolate is a VM instance with its own heap
• ⼀一个隔离区：⼀一个 v8 堆
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句句柄之“局部句句柄”
• template class Local {}
• Because the garbage collector may move objects,
it is unsafe to point directly to an object.
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句句柄之“局部句句柄”
• template class Local {}
• An object reference managed by the v8 garbage
collector.
• A local handle is a pointer to an object. All V8
objects are accessed using handles, they are
necessary because of the way the V8 garbage
collector works.
• ⼀一个局部句句柄：⼀一个 v8 堆上的对象
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句句柄之“持久句句柄”
• Used when keeping a reference to an object for
more than one function call, or when handle
lifetimes do not correspond to C++ scopes.
• A UniquePersistent handle relies on
C++ constructors and destructors to manage the
lifetime of the underlying object.
• A Persistent can be constructed with
its constructor, but must be explicitly cleared with
Persistent::Reset.
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“句句柄区域”
• class V8_EXPORT HandleScope {}
• A stack-allocated class that governs a number of
local handles.
• a container for any number of handles. When
you've finished with your handles, instead of
deleting each one individually you can simply
delete their scope.
• ⼀一个句句柄区域：N 个句句柄
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~HandleScope, is called the handle scope is deleted. Objects
referred to by handles within the deleted handle scope are
eligible for removal in the next garbage collection
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“上下⽂文”
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“上下⽂文”
• class V8_EXPORT Context {}
• JavaScript provides a set of built-in utility functions
and objects that can be changed by JavaScript code.
• Creation of contexts implies creating the built-in
objects and parsing the built-in JavaScript code (with
cache)
• each window and iframe in a browser can have its
own fresh JavaScript environment.
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“上下⽂文”
• class V8_EXPORT Context {}
• A sandboxed execution context with its own set of
built-in objects and functions.
• an execution environment that allows separate,
unrelated, JavaScript code to run in a single
instance of V8. You must explicitly specify the
context in which you want any JavaScript code to
be run.
v8 GC 特征
• “stop-the-world”
stops program execution when performing a garbage
collection cycle
• “generational”
processes only part of the object heap in most garbage
collection cycles. This minimises the impact of stopping
the application
• “accurate”
always knows exactly where all objects and pointers are in
memory. This avoids falsely identifying objects as pointers
which can result in memory leaks.
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libuv 初探
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libuv
• supports Linux via epoll
• supports Windows via Microsoft IOCP
• supports Mac OS X via kqueue
• same API on Linux, Windows, Mac
• Little dependencies (On node-v0.9.0's version of
libuv, the dependency on libev was removed)
“句句柄”
• Handles represent long-lived objects capable of
performing certain operations while active.
• e.g.: a prepare handle gets its callback called once
every loop iteration when active
• e.g.: a TCP server handle get its connection
callback called every time there is a new
connection.
“请求”
• Requests represent (typically) short-lived
operations. These operations can be performed
over a handle
• e.g.: write requests are used to write data on a
handle
• e.g.(standalone): getaddrinfo requests don’t need
a handle they run directly on the loop
事件循环
• tied to a single thread
• all (network) I/O is performed on non-blocking
sockets which are polled using the best
mechanism available on the given platform
• the loop will block waiting for I/O activity on sockets
which have been added to the poller and callbacks
will be fired indicating socket conditions (readable,
writable hangup) so handles can read, write or
perform the desired I/O operation.
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线程池
• a global thread pool on which all loops can queue
work on
• runs blocking file I/O operations
• runs DNS functions (getaddrinfo and getnameinfo)
• runs User specified code via uv_queue_work()
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(possibly)
• linux AIO (supported in the kernel)
• posix AIO (supported by linux, Mac OS X, BSD,
solaris, AIX etc.)
• Windows’ overlapped I/O