libuv API详解与实战示例

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"libuv API说明及用例，英文文档，适用于多平台，专注于异步I/O操作，主要被Node.js、Luvit、Julia、pyuv等使用。文档包含了错误报告指引、全面的特性列表，如事件循环、异步网络和DNS解析、文件系统操作等。" libuv是一个跨平台的支持库，最初是为了Node.js开发，但已被多个项目广泛采用。其核心功能包括： 1. **全面的事件循环**：libuv使用epoll（Linux）、kqueue（FreeBSD、MacOSX）、IOCP（Windows）或事件端口等机制来提供高效、低延迟的事件通知。事件循环是libuv异步操作的基础。 2. **异步TCP和UDP套接字**：libuv支持创建和管理非阻塞的网络连接，允许在不阻塞主线程的情况下进行网络通信。 3. **异步DNS解析**：libuv提供了在后台线程中执行的DNS查询功能，避免了主循环的等待时间。 4. **异步文件和文件系统操作**：用户可以发起如读取、写入、重命名等文件操作，并在完成时得到回调，避免了阻塞当前线程。 5. **文件系统事件**：libuv可以监控文件或目录的变化，如修改、创建、删除等，这对于实时应用和文件监控非常重要。 6. **ANSI转义码控制的TTY**：在终端交互应用中，libuv支持处理控制台输出的ANSI转义序列，实现颜色和其他控制功能。 7. **进程间通信（IPC）**：通过Unix域套接字或命名管道（Windows）实现进程间的通信和资源共享。 8. **子进程**：libuv允许创建和管理子进程，可以用来执行命令或协调其他程序。 9. **线程池**：libuv内部维护一个线程池，用于执行CPU密集型任务，避免单线程阻塞。 10. **信号处理**：libuv提供了处理操作系统信号的接口，如SIGINT、SIGTERM等，帮助应用程序优雅地响应退出请求。 11. **高分辨率时钟**：libuv提供了获取高精度时间的函数，对于需要精确计时的场景非常有用。 12. **线程和同步原语**：libuv还提供了线程、互斥锁、条件变量等同步工具，以保证多线程环境下的数据安全。 libuv的文档详细介绍了这些特性和如何使用它们，同时也鼓励用户在发现错误时通过发送Pull Request来帮助改进文档。对于开发者来说，libuv是一个强大且灵活的工具，它简化了跨平台的异步编程，是构建高性能、非阻塞应用的理想选择。

libuv documentation, Release 1.12.1-dev

UV_ENOTCONN

socket is not connected

UV_ENOTDIR

not a directory

UV_ENOTEMPTY

directory not empty

UV_ENOTSOCK

socket operation on non-socket

UV_ENOTSUP

operation not supported on socket

UV_EPERM

operation not permitted

UV_EPIPE

broken pipe

UV_EPROTO

protocol error

UV_EPROTONOSUPPORT

protocol not supported

UV_EPROTOTYPE

protocol wrong type for socket

UV_ERANGE

result too large

UV_EROFS

read-only ﬁle system

UV_ESHUTDOWN

cannot send after transport endpoint shutdown

UV_ESPIPE

invalid seek

UV_ESRCH

no such process

UV_ETIMEDOUT

connection timed out

UV_ETXTBSY

text ﬁle is busy

UV_EXDEV

cross-device link not permitted

UV_UNKNOWN

unknown error

UV_EOF

end of ﬁle

UV_ENXIO

no such device or address

12 Chapter 3. Documentation

libuv documentation, Release 1.12.1-dev

handles and requests have been closed, or it will return UV_EBUSY. After this function returns, the user can

free the memory allocated for the loop.

uv_loop_t* uv_default_loop(void)

Returns the initialized default loop. It may return NULL in case of allocation failure.

This function is just a convenient way for having a global loop throughout an application, the default loop is in

no way different than the ones initialized with uv_loop_init(). As such, the default loop can (and should)

be closed with uv_loop_close() so the resources associated with it are freed.

int uv_run(uv_loop_t* loop, uv_run_mode mode)

This function runs the event loop. It will act differently depending on the speciﬁed mode:

•UV_RUN_DEFAULT: Runs the event loop until there are no more active and referenced handles or re-

quests. Returns non-zero if uv_stop() was called and there are still active handles or requests. Returns

zero in all other cases.

•UV_RUN_ONCE: Poll for i/o once. Note that this function blocks if there are no pending callbacks.

Returns zero when done (no active handles or requests left), or non-zero if more callbacks are expected

(meaning you should run the event loop again sometime in the future).

•UV_RUN_NOWAIT: Poll for i/o once but don’t block if there are no pending callbacks. Returns zero if

done (no active handles or requests left), or non-zero if more callbacks are expected (meaning you should

run the event loop again sometime in the future).

int uv_loop_alive(const uv_loop_t* loop)

Returns non-zero if there are active handles or request in the loop.

void uv_stop(uv_loop_t* loop)

Stop the event loop, causing uv_run() to end as soon as possible. This will happen not sooner than the next

loop iteration. If this function was called before blocking for i/o, the loop won’t block for i/o on this iteration.

size_t uv_loop_size(void)

Returns the size of the uv_loop_t structure. Useful for FFI binding writers who don’t want to know the structure

layout.

int uv_backend_fd(const uv_loop_t* loop)

Get backend ﬁle descriptor. Only kqueue, epoll and event ports are supported.

This can be used in conjunction with uv_run(loop, UV_RUN_NOWAIT) to poll in one thread and run the event

loop’s callbacks in another see test/test-embed.c for an example.

Note: Embedding a kqueue fd in another kqueue pollset doesn’t work on all platforms. It’s not an error to add

the fd but it never generates events.

int uv_backend_timeout(const uv_loop_t* loop)

Get the poll timeout. The return value is in milliseconds, or -1 for no timeout.

uint64_t uv_now(const uv_loop_t* loop)

Return the current timestamp in milliseconds. The timestamp is cached at the start of the event loop tick, see

uv_update_time() for details and rationale.

The timestamp increases monotonically from some arbitrary point in time. Don’t make assumptions about the

starting point, you will only get disappointed.

Note: Use uv_hrtime() if you need sub-millisecond granularity.

3.2. API documentation 15

libuv documentation, Release 1.12.1-dev

void uv_update_time(uv_loop_t* loop)

Update the event loop’s concept of “now”. Libuv caches the current time at the start of the event loop tick in

order to reduce the number of time-related system calls.

You won’t normally need to call this function unless you have callbacks that block the event loop for longer

periods of time, where “longer” is somewhat subjective but probably on the order of a millisecond or more.

void uv_walk(uv_loop_t* loop, uv_walk_cb walk_cb, void* arg)

Walk the list of handles: walk_cb will be executed with the given arg.

int uv_loop_fork(uv_loop_t* loop)

New in version 1.12.0.

Reinitialize any kernel state necessary in the child process after a fork(2) system call.

Previously started watchers will continue to be started in the child process.

It is necessary to explicitly call this function on every event loop created in the parent process that you plan to

continue to use in the child, including the default loop (even if you don’t continue to use it in the parent). This

function must be called before calling uv_run() or any other API function using the loop in the child. Failure

to do so will result in undeﬁned behaviour, possibly including duplicate events delivered to both parent and child

or aborting the child process.

When possible, it is preferred to create a new loop in the child process instead of reusing a loop created in the

parent. New loops created in the child process after the fork should not use this function.

This function is not implemented on Windows, where it returns UV_ENOSYS.

Caution: This function is experimental. It may contain bugs, and is subject to change or removal. API and

ABI stability is not guaranteed.

Note: On Mac OS X, if directory FS event handles were in use in the parent process for any event loop, the

child process will no longer be able to use the most efﬁcient FSEvent implementation. Instead, uses of directory

FS event handles in the child will fall back to the same implementation used for ﬁles and on other kqueue-based

systems.

Caution: On AIX and SunOS, FS event handles that were already started in the parent process at the time of

forking will not deliver events in the child process; they must be closed and restarted. On all other platforms,

they will continue to work normally without any further intervention.

Caution: Any previous value returned from :c:func‘uv_backend_fd‘ is now invalid. That function must be

called again to determine the correct backend ﬁle descriptor.

uv_handle_t — Base handle

uv_handle_t is the base type for all libuv handle types.

Structures are aligned so that any libuv handle can be cast to uv_handle_t. All API functions deﬁned here work with

any handle type.

16 Chapter 3. Documentation

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