#include "uv.h"#include "uv-common.h"#include#include #include struct poll_ctx { uv_fs_poll_t* parent_handle; /* NULL if parent has been stopped or closed */ int busy_polling; unsigned int interval; uint64_t start_time; uv_loop_t* loop; uv_fs_poll_cb poll_cb; uv_timer_t timer_handle; uv_fs_t fs_req; /* TODO(bnoordhuis) mark fs_req internal */ uv_stat_t statbuf; // 字符串的值追加在结构体后面 char path[1]; /* variable length */};static int statbuf_eq(const uv_stat_t* a, const uv_stat_t* b);static void poll_cb(uv_fs_t* req);static void timer_cb(uv_timer_t* timer);static void timer_close_cb(uv_handle_t* handle);static uv_stat_t zero_statbuf;// 初始化uv_fs_poll_t结构int uv_fs_poll_init(uv_loop_t* loop, uv_fs_poll_t* handle) { uv__handle_init(loop, (uv_handle_t*)handle, UV_FS_POLL); return 0;}int uv_fs_poll_start(uv_fs_poll_t* handle, uv_fs_poll_cb cb, const char* path, unsigned int interval) { struct poll_ctx* ctx; uv_loop_t* loop; size_t len; int err; if (uv__is_active(handle)) return 0; loop = handle->loop; len = strlen(path); // 分配一块内存存上下文结构体和path对应的字符串 ctx = uv__calloc(1, sizeof(*ctx) + len); if (ctx == NULL) return UV_ENOMEM; // 初始化上下文结构 ctx->loop = loop; // 内容改变时的回调 ctx->poll_cb = cb; // 多久检测一次内容是否变化 ctx->interval = interval ? interval : 1; // 开始的时间点 ctx->start_time = uv_now(loop); // 上下文对应的handle结构 ctx->parent_handle = handle; memcpy(ctx->path, path, len + 1); // 初始化一个定时器 err = uv_timer_init(loop, &ctx->timer_handle); if (err < 0) goto error; // 设置UV_HANDLE_INTERNAL标记位 ctx->timer_handle.flags |= UV_HANDLE_INTERNAL; //清除UV_HANDLE_REF标记 uv__handle_unref(&ctx->timer_handle); // 异步获取path对应的文件的信息，获取到后执行poll_cb err = uv_fs_stat(loop, &ctx->fs_req, ctx->path, poll_cb); if (err < 0) goto error; // 挂载上下文到handle handle->poll_ctx = ctx; // 激活该handle，但不增加handle的active数 uv__handle_start(handle); return 0;error: // 出错则释放分配的内存 uv__free(ctx); return err;}// 停止pollint uv_fs_poll_stop(uv_fs_poll_t* handle) { struct poll_ctx* ctx; if (!uv__is_active(handle)) return 0; ctx = handle->poll_ctx; assert(ctx != NULL); assert(ctx->parent_handle != NULL); // 解除关联 ctx->parent_handle = NULL; handle->poll_ctx = NULL; /* Close the timer if it's active. If it's inactive, there's a stat request * in progress and poll_cb will take care of the cleanup. */ // 停止定时器，设置回调为time_close_cb，设置状态为closing if (uv__is_active(&ctx->timer_handle)) uv_close((uv_handle_t*)&ctx->timer_handle, timer_close_cb); uv__handle_stop(handle); return 0;}// 获取pathint uv_fs_poll_getpath(uv_fs_poll_t* handle, char* buffer, size_t* size) { struct poll_ctx* ctx; size_t required_len; if (!uv__is_active(handle)) { *size = 0; return UV_EINVAL; } ctx = handle->poll_ctx; assert(ctx != NULL); required_len = strlen(ctx->path); if (required_len >= *size) { *size = required_len + 1; return UV_ENOBUFS; } memcpy(buffer, ctx->path, required_len); *size = required_len; buffer[required_len] = '\0'; return 0;}void uv__fs_poll_close(uv_fs_poll_t* handle) { uv_fs_poll_stop(handle);}// 定时器到期执行的回调static void timer_cb(uv_timer_t* timer) { struct poll_ctx* ctx; ctx = container_of(timer, struct poll_ctx, timer_handle); assert(ctx->parent_handle != NULL); assert(ctx->parent_handle->poll_ctx == ctx); ctx->start_time = uv_now(ctx->loop); // 再次获取stat信息 if (uv_fs_stat(ctx->loop, &ctx->fs_req, ctx->path, poll_cb)) abort();}// 获取到stat后执行的回调static void poll_cb(uv_fs_t* req) { uv_stat_t* statbuf; struct poll_ctx* ctx; uint64_t interval; ctx = container_of(req, struct poll_ctx, fs_req); if (ctx->parent_handle == NULL) { /* handle has been stopped or closed */ uv_close((uv_handle_t*)&ctx->timer_handle, timer_close_cb); uv_fs_req_cleanup(req); return; } if (req->result != 0) { if (ctx->busy_polling != req->result) { ctx->poll_cb(ctx->parent_handle, req->result, &ctx->statbuf, &zero_statbuf); ctx->busy_polling = req->result; } goto out; } statbuf = &req->statbuf; // 第一次不执行回调，因为没有可对比的stat，第二次及后续的操作才可能执行回调，因为第一次执行的时候置busy_polling=1 if (ctx->busy_polling != 0) // 出错或者stat发生了变化则执行回调 if (ctx->busy_polling < 0 || !statbuf_eq(&ctx->statbuf, statbuf)) ctx->poll_cb(ctx->parent_handle, 0, &ctx->statbuf, statbuf); // 保存当前获取到的stat信息，置1 ctx->statbuf = *statbuf; ctx->busy_polling = 1;out: uv_fs_req_cleanup(req); if (ctx->parent_handle == NULL) { /* handle has been stopped by callback */ uv_close((uv_handle_t*)&ctx->timer_handle, timer_close_cb); return; } /* Reschedule timer, subtract the delay from doing the stat(). */ /* 假设在开始时间点为1，interval为10的情况下执行了stat，stat完成执行并执行poll_cb回调的时间点是 3，那么定时器的超时时间则为10-3=7，即7个单位后就要触发超时，而不是10，是因为stat阻塞消耗了3个单位的 时间，所以下次执行超时回调函数时说明从start时间点开始算，已经经历了x单位各interval，然后超时回调里又 执行了stat函数，再到执行stat回调，这个时间点即now=start+x单位个interval+stat消耗的时间。得出now-start 为interval的x倍+stat消耗，即对interval取余可得到stat消耗，所以 当前轮，定时器的超时时间为interval - ((now-start) % interval) */ interval = ctx->interval; interval -= (uv_now(ctx->loop) - ctx->start_time) % interval; if (uv_timer_start(&ctx->timer_handle, timer_cb, interval, 0)) abort();}// 释放上下文结构体的内存static void timer_close_cb(uv_handle_t* handle) { uv__free(container_of(handle, struct poll_ctx, timer_handle));}static int statbuf_eq(const uv_stat_t* a, const uv_stat_t* b) { return a->st_ctim.tv_nsec == b->st_ctim.tv_nsec && a->st_mtim.tv_nsec == b->st_mtim.tv_nsec && a->st_birthtim.tv_nsec == b->st_birthtim.tv_nsec && a->st_ctim.tv_sec == b->st_ctim.tv_sec && a->st_mtim.tv_sec == b->st_mtim.tv_sec && a->st_birthtim.tv_sec == b->st_birthtim.tv_sec && a->st_size == b->st_size && a->st_mode == b->st_mode && a->st_uid == b->st_uid && a->st_gid == b->st_gid && a->st_ino == b->st_ino && a->st_dev == b->st_dev && a->st_flags == b->st_flags && a->st_gen == b->st_gen;}#if defined(_WIN32)#include "win/internal.h"#include "win/handle-inl.h"void uv__fs_poll_endgame(uv_loop_t* loop, uv_fs_poll_t* handle) { assert(handle->flags & UV_HANDLE_CLOSING); assert(!(handle->flags & UV_HANDLE_CLOSED)); uv__handle_close(handle);}复制代码
文件监听的原理是，第一次先执行stat函数获取文件基本信息，然后在stat的回调函数里设置定时器，定时器超时后会执行stat，然后获取stat信息，再次执行stat回调函数重新设置定时器，如此反复，如果stat不一样就执行用户的回调。