使用functrace輔助進(jìn)行Go項(xiàng)目源碼分析

在《像跟蹤分布式服務(wù)調(diào)用那樣跟蹤Go函數(shù)調(diào)用鏈》^[1]：https://github.com/bigwhite/functrace。這個(gè)小工具不僅僅是分享給大家的，我自己在工作和學(xué)習(xí)時(shí)也在使用。最近發(fā)現(xiàn)這個(gè)小工具在閱讀和分析某個(gè)Go項(xiàng)目源碼時(shí)也能起到關(guān)鍵的輔助作用。這里就和大家簡單講解一下如何用functrace來輔助Go源碼閱讀和分析。

程序員的日常離不開“源碼閱讀和分析”，日常閱讀代碼的姿勢無非是這么幾種（或幾種的組合）：

• 結(jié)合源碼編輯器或IDE提供的強(qiáng)大的源碼交叉索引和跳轉(zhuǎn)功能在一個(gè)龐大的源碼庫中建立起代碼間的聯(lián)系；
• 將代碼跑起來，在代碼中加上一些print輸出，跟蹤執(zhí)行流并畫出；
• 也有人喜歡用調(diào)試器從一點(diǎn)（通常是main）開始單步跟蹤執(zhí)行流。

無論哪一種方式，最終只要時(shí)間夠長，態(tài)度到位，總是會(huì)將代碼分析出個(gè)七七八八的。

就筆者來看，無論是哪種范式：命令式、面向?qū)ο蟆⒑瘮?shù)式，最終梳理出來的源碼脈絡(luò)都是建立在執(zhí)行基本單元(函數(shù)或方法)上，代碼的執(zhí)行主線（并發(fā)程序會(huì)有若干條）本質(zhì)上就是一條函數(shù)/方法調(diào)用鏈。只要把這條鏈理出來，代碼理解起來就不難了。上述的代碼閱讀方法實(shí)質(zhì)也是參照這個(gè)邏輯的。只是對于調(diào)用層次較深，還伴隨有回調(diào)的代碼，梳理調(diào)用鏈難度高、效率低。

functrace最初用于跟蹤函數(shù)調(diào)用鏈（得益于Go核心開發(fā)團(tuán)隊(duì)公開的抽象語法樹AST API^[2]），但如果在閱讀代碼時(shí)直接用functrace輸出函數(shù)調(diào)用鏈，那將大幅提高我們源碼閱讀分析的效率。下面我們就用一個(gè)樣例項(xiàng)目來試試如何用functrace梳理出代碼的執(zhí)行主線。

我們以Go高性能、輕量級(jí)、非阻塞的事件驅(qū)動(dòng)網(wǎng)絡(luò)框架gnet為例，來看看如何閱讀分析gnet的源碼。首先我們需要安裝functrace工具：

$go install github.com/bigwhite/functrace/cmd/gen@latest
go: downloading github.com/bigwhite/functrace v0.0.0-20210603024853-ccab68a2604c
go: downloading golang.org/x/tools v0.0.0-20201204062850-545788942d5f

$gen -h
[gen -h]
gen [-w] xxx.go
  -w write result to (source) file instead of stdout

接下來，我們下載要進(jìn)行源碼分析的gnet源碼：

$git clone [email protected]:panjf2000/gnet.git

我們進(jìn)入gnet目錄，現(xiàn)在我們可以使用gen命令為任意go源文件添加“跟蹤設(shè)施”了，比如：

$gen -w gnet.go
[gen -w gnet.go]
add trace for gnet.go ok

$ git diff gnet.go
diff --git a/gnet.go b/gnet.go
index b4c04a5..a7afe2b 100644
--- a/gnet.go
+++ b/gnet.go
@@ -29,6 +29,7 @@ import (
        "sync"
        "time"
 
+       "github.com/bigwhite/functrace"
        "github.com/panjf2000/gnet/errors"
        "github.com/panjf2000/gnet/internal"
        "github.com/panjf2000/gnet/internal/logging"
... ...

我們可以這樣根據(jù)自己的需要在特定的go源文件上添加“跟蹤設(shè)施”，但是多數(shù)情況下，我們也可以通過腳本為項(xiàng)目內(nèi)所有g(shù)o源文件批量添加“跟蹤設(shè)施”，functrace項(xiàng)目提供了一個(gè)簡單的腳本batch_add_trace.sh^[3]，下面我們就來通過該腳本將gnet下的go源文件批量加上函數(shù)跟蹤設(shè)施：

下載functrace源碼：

$git clone https://github.com/bigwhite/functrace.git

將functrace/scripts/batch_add_trace.sh 拷貝到上面gnet目錄下并執(zhí)行下面命令：

# bash batch_add_trace.sh 
... ...
[gen -w ./server_unix.go]
add trace for ./server_unix.go ok
[gen -w ./internal/socket/sockopts_posix.go]
add trace for ./internal/socket/sockopts_posix.go ok
... ...
[gen -w ./ringbuffer/ring_buffer_test.go]
add trace for ./ringbuffer/ring_buffer_test.go ok
[gen -w ./ringbuffer/ring_buffer.go]
add trace for ./ringbuffer/ring_buffer.go ok
[gen -w ./pool/bytebuffer/bytebuffer.go]
no trace added for ./pool/bytebuffer/bytebuffer.go
[gen -w ./pool/goroutine/goroutine.go]
add trace for ./pool/goroutine/goroutine.go ok
[gen -w ./pool/ringbuffer/ringbuffer.go]
add trace for ./pool/ringbuffer/ringbuffer.go ok
[gen -w ./loop_linux.go]
add trace for ./loop_linux.go ok
[gen -w ./server_windows.go]
add trace for ./server_windows.go ok

接下來我們編寫一個(gè)基于gnet的程序，我們就使用gnet參加TechEmpower^[4]的那份代碼：

//main.go
package main

import (
 "bytes"
 "flag"
 "fmt"
 "log"
 "runtime"
 "time"

 "github.com/panjf2000/gnet"
)

type httpServer struct {
 *gnet.EventServer
}

type httpCodec struct {
 delimiter []byte
}

func (hc *httpCodec) Encode(c gnet.Conn, buf []byte) (out []byte, err error) {
 return buf, nil
}

func (hc *httpCodec) Decode(c gnet.Conn) (out []byte, err error) {
 buf := c.Read()
 if buf == nil {
  return
 }
 c.ResetBuffer()

 // process the pipeline
 var i int
pipeline:
 if i = bytes.Index(buf, hc.delimiter); i != -1 {
  out = append(out, "HTTP/1.1 200 OK\r\nServer: gnet\r\nContent-Type: text/plain\r\nDate: "...)
  out = time.Now().AppendFormat(out, "Mon, 02 Jan 2006 15:04:05 GMT")
  out = append(out, "\r\nContent-Length: 13\r\n\r\nHello, World!"...)
  buf = buf[i+4:]
  goto pipeline
 }
 // request not ready, yet
 return
}

func (hs *httpServer) OnInitComplete(srv gnet.Server) (action gnet.Action) {
 log.Printf("HTTP server is listening on %s (multi-cores: %t, loops: %d)\n",
  srv.Addr.String(), srv.Multicore, srv.NumEventLoop)
 return
}

func (hs *httpServer) React(frame []byte, c gnet.Conn) (out []byte, action gnet.Action) {
 // handle the request
 out = frame
 return
}

func init() {
 runtime.GOMAXPROCS(runtime.NumCPU() * 2)
}

func main() {
 var port int
 var multicore bool

 // Example command: go run main.go --port 8080 --multicore=true
 flag.IntVar(&port, "port", 8080, "server port")
 flag.BoolVar(&multicore, "multicore", true, "multicore")
 flag.Parse()

 http := new(httpServer)
 hc := &httpCodec{delimiter: []byte("\r\n\r\n")}

 // Start serving!
 log.Fatal(gnet.Serve(http, fmt.Sprintf("tcp://:%d", port), gnet.WithMulticore(multicore), gnet.WithCodec(hc)))
}

構(gòu)建這份代碼：

$go mod init gnet-demo
$go get github.com/panjf2000/gnet
go: downloading github.com/panjf2000/gnet v1.4.5
go get: added github.com/panjf2000/gnet v1.4.5

//修改go.mod，使用replace讓gnet-demo使用本地的gnet代碼
$cat go.mod
module gnet-demo

go 1.16

replace github.com/panjf2000/gnet => /root/go/src/github.com/panjf2000/gnet

require (
        github.com/panjf2000/gnet v1.4.5
)

$go get github.com/bigwhite/functrace
go get: added github.com/bigwhite/functrace v0.0.0-20210603024853-ccab68a2604c

$go build -tags trace //-tags trace務(wù)必不能省略，這個(gè)是開啟functrace的關(guān)鍵

構(gòu)建后，我們來執(zhí)行構(gòu)建出的可執(zhí)行程序：gnet-demo：

$ go build -tags trace
root@VM-0-12-ubuntu:~/test/go/gnet-demo# ./gnet-demo
g[01]: ->github.com/panjf2000/gnet/internal/socket.maxListenerBacklog
g[01]: <-github.com/panjf2000/gnet/internal/socket.maxListenerBacklog
g[01]: ->github.com/panjf2000/gnet/ringbuffer.New
g[01]: <-github.com/panjf2000/gnet/ringbuffer.New
g[01]: ->github.com/panjf2000/gnet/internal/logging.init.0
g[01]: <-github.com/panjf2000/gnet/internal/logging.init.0
g[01]: ->github.com/panjf2000/gnet.WithMulticore
g[01]: <-github.com/panjf2000/gnet.WithMulticore
g[01]: ->github.com/panjf2000/gnet.WithCodec
g[01]: <-github.com/panjf2000/gnet.WithCodec
g[01]: ->github.com/panjf2000/gnet.Serve
g[01]:  ->github.com/panjf2000/gnet.loadOptions
g[01]:  <-github.com/panjf2000/gnet.loadOptions
g[01]:  ->github.com/panjf2000/gnet.parseProtoAddr
g[01]:  <-github.com/panjf2000/gnet.parseProtoAddr
g[01]:  ->github.com/panjf2000/gnet.initListener
g[01]:   ->github.com/panjf2000/gnet.(*listener).normalize
g[01]:    ->github.com/panjf2000/gnet/internal/socket.TCPSocket
g[01]:     ->github.com/panjf2000/gnet/internal/socket.tcpSocket
g[01]:      ->github.com/panjf2000/gnet/internal/socket.getTCPSockaddr
g[01]:       ->github.com/panjf2000/gnet/internal/socket.determineTCPProto
g[01]:       <-github.com/panjf2000/gnet/internal/socket.determineTCPProto
g[01]:      <-github.com/panjf2000/gnet/internal/socket.getTCPSockaddr
g[01]:      ->github.com/panjf2000/gnet/internal/socket.sysSocket
g[01]:      <-github.com/panjf2000/gnet/internal/socket.sysSocket
g[01]:      ->github.com/panjf2000/gnet/internal/socket.SetNoDelay
g[01]:      <-github.com/panjf2000/gnet/internal/socket.SetNoDelay
g[01]:     <-github.com/panjf2000/gnet/internal/socket.tcpSocket
g[01]:    <-github.com/panjf2000/gnet/internal/socket.TCPSocket
g[01]:   <-github.com/panjf2000/gnet.(*listener).normalize
g[01]:  <-github.com/panjf2000/gnet.initListener
g[01]:  ->github.com/panjf2000/gnet.serve
2021/06/03 14:53:30 HTTP server is listening on :8080 (multi-cores: true, loops: 1)
g[01]:   ->github.com/panjf2000/gnet.(*server).start
g[01]:    ->github.com/panjf2000/gnet.(*server).activateReactors
g[01]:     ->github.com/panjf2000/gnet/internal/netpoll.OpenPoller
g[01]:      ->github.com/panjf2000/gnet/internal/netpoll.(*Poller).AddRead
g[01]:      <-github.com/panjf2000/gnet/internal/netpoll.(*Poller).AddRead
g[01]:      ->github.com/panjf2000/gnet/internal/netpoll/queue.NewLockFreeQueue
g[01]:      <-github.com/panjf2000/gnet/internal/netpoll/queue.NewLockFreeQueue
g[01]:     <-github.com/panjf2000/gnet/internal/netpoll.OpenPoller
g[01]:     ->github.com/panjf2000/gnet.(*roundRobinLoadBalancer).register
g[01]:     <-github.com/panjf2000/gnet.(*roundRobinLoadBalancer).register
g[01]:     ->github.com/panjf2000/gnet.(*server).startSubReactors
g[01]:      ->github.com/panjf2000/gnet.(*roundRobinLoadBalancer).iterate
g[01]:      <-github.com/panjf2000/gnet.(*roundRobinLoadBalancer).iterate
g[01]:     <-github.com/panjf2000/gnet.(*server).startSubReactors
g[01]:     ->github.com/panjf2000/gnet/internal/netpoll.OpenPoller
g[01]:      ->github.com/panjf2000/gnet/internal/netpoll.(*Poller).AddRead
g[01]:      <-github.com/panjf2000/gnet/internal/netpoll.(*Poller).AddRead
g[01]:      ->github.com/panjf2000/gnet/internal/netpoll/queue.NewLockFreeQueue
g[01]:      <-github.com/panjf2000/gnet/internal/netpoll/queue.NewLockFreeQueue
g[01]:     <-github.com/panjf2000/gnet/internal/netpoll.OpenPoller
g[01]:     ->github.com/panjf2000/gnet/internal/netpoll.(*Poller).AddRead
g[01]:     <-github.com/panjf2000/gnet/internal/netpoll.(*Poller).AddRead
g[01]:    <-github.com/panjf2000/gnet.(*server).activateReactors
g[01]:   <-github.com/panjf2000/gnet.(*server).start
g[01]:   ->github.com/panjf2000/gnet.(*server).stop
g[01]:    ->github.com/panjf2000/gnet.(*server).waitForShutdown
g[07]: ->github.com/panjf2000/gnet.(*server).activateMainReactor
g[07]:  ->github.com/panjf2000/gnet/internal/netpoll.(*Poller).Polling
g[07]:   ->github.com/panjf2000/gnet/internal/netpoll.newEventList
g[07]:   <-github.com/panjf2000/gnet/internal/netpoll.newEventList
g[06]: ->github.com/panjf2000/gnet.(*server).activateSubReactor
g[06]:  ->github.com/panjf2000/gnet/internal/netpoll.(*Poller).Polling
g[06]:   ->github.com/panjf2000/gnet/internal/netpoll.newEventList
g[06]:   <-github.com/panjf2000/gnet/internal/netpoll.newEventList

我們看到gnet的執(zhí)行主線被清晰的打印出來，通過輸出的函數(shù)所在包我們可以輕松找到對應(yīng)的源文件。g[01]這goroutine顯然是main goroutine，整個(gè)程序的初始化線索通過跟蹤g[01]的函數(shù)鏈便一目了然。

如果我們要看gnet是如何處理一個(gè)外部鏈接的，我們可以向gnet-demo建立一個(gè)連接，看看gnet-demo的輸出。

我們通過curl命令向gnet-demo發(fā)起一個(gè)http請求：

$curl localhost:8080
Hello, World!

gnet-demo輸出：

g[07]:   ->github.com/panjf2000/gnet.(*server).acceptNewConnection
g[07]:    ->github.com/panjf2000/gnet/internal/socket.SockaddrToTCPOrUnixAddr
g[07]:     ->github.com/panjf2000/gnet/internal/socket.sockaddrInet6ToIPAndZone
g[07]:      ->github.com/panjf2000/gnet/internal/socket.ip6ZoneToString
g[07]:      <-github.com/panjf2000/gnet/internal/socket.ip6ZoneToString
g[07]:     <-github.com/panjf2000/gnet/internal/socket.sockaddrInet6ToIPAndZone
g[07]:    <-github.com/panjf2000/gnet/internal/socket.SockaddrToTCPOrUnixAddr
g[07]:    ->github.com/panjf2000/gnet.(*roundRobinLoadBalancer).next
g[07]:    <-github.com/panjf2000/gnet.(*roundRobinLoadBalancer).next
g[07]:    ->github.com/panjf2000/gnet.newTCPConn
g[07]:     ->github.com/panjf2000/gnet/pool/ringbuffer.Get
g[07]:      ->github.com/panjf2000/gnet/pool/ringbuffer.(*Pool).Get
g[07]:       ->github.com/panjf2000/gnet/ringbuffer.New
g[07]:       <-github.com/panjf2000/gnet/ringbuffer.New
g[07]:      <-github.com/panjf2000/gnet/pool/ringbuffer.(*Pool).Get
g[07]:     <-github.com/panjf2000/gnet/pool/ringbuffer.Get
g[07]:     ->github.com/panjf2000/gnet/pool/ringbuffer.Get
g[07]:      ->github.com/panjf2000/gnet/pool/ringbuffer.(*Pool).Get
g[07]:       ->github.com/panjf2000/gnet/ringbuffer.New
g[07]:       <-github.com/panjf2000/gnet/ringbuffer.New
g[07]:      <-github.com/panjf2000/gnet/pool/ringbuffer.(*Pool).Get
g[07]:     <-github.com/panjf2000/gnet/pool/ringbuffer.Get
g[07]:    <-github.com/panjf2000/gnet.newTCPConn
g[07]:    ->github.com/panjf2000/gnet/internal/netpoll.(*Poller).Trigger
g[07]:     ->github.com/panjf2000/gnet/internal/netpoll/queue.(*lockFreeQueue).Enqueue
g[07]:      ->github.com/panjf2000/gnet/internal/netpoll/queue.load
g[07]:      <-github.com/panjf2000/gnet/internal/netpoll/queue.load
g[07]:      ->github.com/panjf2000/gnet/internal/netpoll/queue.load
g[07]:      <-github.com/panjf2000/gnet/internal/netpoll/queue.load
g[07]:      ->github.com/panjf2000/gnet/internal/netpoll/queue.load
g[07]:      <-github.com/panjf2000/gnet/internal/netpoll/queue.load
g[07]:      ->github.com/panjf2000/gnet/internal/netpoll/queue.cas
g[07]:      <-github.com/panjf2000/gnet/internal/netpoll/queue.cas
g[07]:      ->github.com/panjf2000/gnet/internal/netpoll/queue.cas
g[07]:      <-github.com/panjf2000/gnet/internal/netpoll/queue.cas
g[07]:     <-github.com/panjf2000/gnet/internal/netpoll/queue.(*lockFreeQueue).Enqueue
g[07]:    <-github.com/panjf2000/gnet/internal/netpoll.(*Poller).Trigger
g[07]:   <-github.com/panjf2000/gnet.(*server).acceptNewConnection
g[07]:   ->github.com/panjf2000/gnet/internal/netpoll.(*eventList).shrink
g[07]:   <-github.com/panjf2000/gnet/internal/netpoll.(*eventList).shrink
g[06]:   ->github.com/panjf2000/gnet/internal/netpoll/queue.(*lockFreeQueue).Dequeue
g[06]:    ->github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:    <-github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:    ->github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:    <-github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:    ->github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:    <-github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:    ->github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:    <-github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:    ->github.com/panjf2000/gnet/internal/netpoll/queue.cas
g[06]:    <-github.com/panjf2000/gnet/internal/netpoll/queue.cas
g[06]:   <-github.com/panjf2000/gnet/internal/netpoll/queue.(*lockFreeQueue).Dequeue
g[06]:   ->github.com/panjf2000/gnet/internal/netpoll.(*Poller).AddRead
g[06]:   <-github.com/panjf2000/gnet/internal/netpoll.(*Poller).AddRead
g[06]:   ->github.com/panjf2000/gnet.(*eventloop).loopOpen
g[06]:    ->github.com/panjf2000/gnet.(*eventloop).addConn
g[06]:    <-github.com/panjf2000/gnet.(*eventloop).addConn
g[06]:    ->github.com/panjf2000/gnet.(*EventServer).OnOpened
g[06]:    <-github.com/panjf2000/gnet.(*EventServer).OnOpened
g[06]:    ->github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).IsEmpty
g[06]:    <-github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).IsEmpty
g[06]:    ->github.com/panjf2000/gnet.(*eventloop).handleAction
g[06]:    <-github.com/panjf2000/gnet.(*eventloop).handleAction
g[06]:   <-github.com/panjf2000/gnet.(*eventloop).loopOpen
g[06]:   ->github.com/panjf2000/gnet/internal/netpoll/queue.(*lockFreeQueue).Dequeue
g[06]:    ->github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:    <-github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:    ->github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:    <-github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:    ->github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:    <-github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:    ->github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:    <-github.com/panjf2000/gnet/internal/netpoll/queue.load
g[06]:   <-github.com/panjf2000/gnet/internal/netpoll/queue.(*lockFreeQueue).Dequeue
g[06]:   ->github.com/panjf2000/gnet/internal/netpoll/queue.(*lockFreeQueue).Empty
g[06]:   <-github.com/panjf2000/gnet/internal/netpoll/queue.(*lockFreeQueue).Empty
g[06]:   ->github.com/panjf2000/gnet/internal/netpoll.(*eventList).shrink
g[06]:   <-github.com/panjf2000/gnet/internal/netpoll.(*eventList).shrink
g[06]:   ->github.com/panjf2000/gnet.(*eventloop).loopRead
g[06]:    ->github.com/panjf2000/gnet.(*conn).read
g[06]:     ->github.com/panjf2000/gnet.(*conn).Read
g[06]:      ->github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).IsEmpty
g[06]:      <-github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).IsEmpty
g[06]:     <-github.com/panjf2000/gnet.(*conn).Read
g[06]:     ->github.com/panjf2000/gnet.(*conn).ResetBuffer
g[06]:      ->github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).Reset
g[06]:      <-github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).Reset
g[06]:     <-github.com/panjf2000/gnet.(*conn).ResetBuffer
g[06]:    <-github.com/panjf2000/gnet.(*conn).read
g[06]:    ->github.com/panjf2000/gnet.(*EventServer).PreWrite
g[06]:    <-github.com/panjf2000/gnet.(*EventServer).PreWrite
g[06]:    ->github.com/panjf2000/gnet.(*conn).write
g[06]:     ->github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).IsEmpty
g[06]:     <-github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).IsEmpty
g[06]:    <-github.com/panjf2000/gnet.(*conn).write
g[06]:    ->github.com/panjf2000/gnet.(*conn).read
g[06]:     ->github.com/panjf2000/gnet.(*conn).Read
g[06]:      ->github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).IsEmpty
g[06]:      <-github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).IsEmpty
g[06]:     <-github.com/panjf2000/gnet.(*conn).Read
g[06]:     ->github.com/panjf2000/gnet.(*conn).ResetBuffer
g[06]:      ->github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).Reset
g[06]:      <-github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).Reset
g[06]:     <-github.com/panjf2000/gnet.(*conn).ResetBuffer
g[06]:    <-github.com/panjf2000/gnet.(*conn).read
g[06]:    ->github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).Write
g[06]:    <-github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).Write
g[06]:   <-github.com/panjf2000/gnet.(*eventloop).loopRead
g[06]:   ->github.com/panjf2000/gnet/internal/netpoll.(*eventList).shrink
g[06]:   <-github.com/panjf2000/gnet/internal/netpoll.(*eventList).shrink
g[06]:   ->github.com/panjf2000/gnet.(*eventloop).loopRead
g[06]:    ->github.com/panjf2000/gnet.(*eventloop).loopCloseConn
g[06]:     ->github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).IsEmpty
g[06]:     <-github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).IsEmpty
g[06]:     ->github.com/panjf2000/gnet/internal/netpoll.(*Poller).Delete
g[06]:     <-github.com/panjf2000/gnet/internal/netpoll.(*Poller).Delete
g[06]:     ->github.com/panjf2000/gnet.(*eventloop).addConn
g[06]:     <-github.com/panjf2000/gnet.(*eventloop).addConn
g[06]:     ->github.com/panjf2000/gnet.(*EventServer).OnClosed
g[06]:     <-github.com/panjf2000/gnet.(*EventServer).OnClosed
g[06]:     ->github.com/panjf2000/gnet.(*conn).releaseTCP
g[06]:      ->github.com/panjf2000/gnet/pool/ringbuffer.Put
g[06]:       ->github.com/panjf2000/gnet/pool/ringbuffer.(*Pool).Put
g[06]:        ->github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).Len
g[06]:        <-github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).Len
g[06]:        ->github.com/panjf2000/gnet/pool/ringbuffer.index
g[06]:        <-github.com/panjf2000/gnet/pool/ringbuffer.index
g[06]:        ->github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).Reset
g[06]:        <-github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).Reset
g[06]:       <-github.com/panjf2000/gnet/pool/ringbuffer.(*Pool).Put
g[06]:      <-github.com/panjf2000/gnet/pool/ringbuffer.Put
g[06]:      ->github.com/panjf2000/gnet/pool/ringbuffer.Put
g[06]:       ->github.com/panjf2000/gnet/pool/ringbuffer.(*Pool).Put
g[06]:        ->github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).Len
g[06]:        <-github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).Len
g[06]:        ->github.com/panjf2000/gnet/pool/ringbuffer.index
g[06]:        <-github.com/panjf2000/gnet/pool/ringbuffer.index
g[06]:        ->github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).Reset
g[06]:        <-github.com/panjf2000/gnet/ringbuffer.(*RingBuffer).Reset
g[06]:       <-github.com/panjf2000/gnet/pool/ringbuffer.(*Pool).Put
g[06]:      <-github.com/panjf2000/gnet/pool/ringbuffer.Put
g[06]:     <-github.com/panjf2000/gnet.(*conn).releaseTCP
g[06]:    <-github.com/panjf2000/gnet.(*eventloop).loopCloseConn
g[06]:   <-github.com/panjf2000/gnet.(*eventloop).loopRead
g[06]:   ->github.com/panjf2000/gnet/internal/netpoll.(*eventList).shrink
g[06]:   <-github.com/panjf2000/gnet/internal/netpoll.(*eventList).shrink

通過gnet-demo輸出，我們可以清晰看到gnet接收一個(gè)連接，在這個(gè)連接上讀寫以及關(guān)閉這個(gè)連接的函數(shù)調(diào)用鏈，有了這個(gè)鏈條，我們再來閱讀gnet源碼就輕松許多了，即便有回調(diào)函數(shù)也沒有問題。

上面輸出的函數(shù)調(diào)用鏈的內(nèi)容已經(jīng)很多了。但如果你還不滿足于這些，比如我還要跟蹤到gnet依賴的golang.org/x/sys中，那可以利用相同思路，將golang.org/x/sys下載到本地，并通過functrace添加跟蹤設(shè)施，并在gnet-demo中用replace換掉golang.org/x/sys，讓其指向本地的sys包代碼。如果覺得信息太多，可以通過gen命令做單個(gè)必要go源文件的跟蹤信息添加，而不必要用批量方式。進(jìn)一步的跟蹤sys包的函數(shù)調(diào)用鏈的作業(yè)就留給大家了，這里就不深入了。

代碼閱讀完成后，我們只需在gnet目錄下執(zhí)行如下命令便可以恢復(fù)gnet原來的面貌：

$git checkout .

參考資料