Go-基础篇-图解启动过程启动过程环境: go1.8 流程图概览步骤解释入口文件 runtime/asm_amd6

启动过程

环境: go1.8

流程图概览

Go语言启动流程 (1).png

步骤解释

入口文件 runtime/asm_amd64.s
- 根据不同的机器对应不同的文件，本文以mac电脑为例
启动入口函数 - _rt0_amd64
- 这是大部分在使用的64位操作系统的通用启动代码，

JMP runtime·rt0_go(SB) 跳到该函数

复制入口参数进入栈中
设置tls线程本地存储
启动G0/启动M0建立关联关系
runtime.check - 运行时检查
args(argc/argv)参数处理
调用runtime.args处理
调用runtime.osinit
- 获取CPU数量
- 获取物理内存页的大小PageSize，为了将来mallocinit使用
调用runtime.schedinit 调度器初始化 - 该处应为启动的核心逻辑(进行各种运行时组件初始化工作，这包括我们的调度器与内存分配器、回收器的初始化)

// The bootstrap sequence is:
//
//	call osinit
//	call schedinit
//	make & queue new G
//	call runtime·mstart
//
// The new G calls runtime·main.
func schedinit() {
	lockInit(&sched.lock, lockRankSched)
	lockInit(&sched.sysmonlock, lockRankSysmon)
	lockInit(&sched.deferlock, lockRankDefer)
	lockInit(&sched.sudoglock, lockRankSudog)
	lockInit(&deadlock, lockRankDeadlock)
	lockInit(&paniclk, lockRankPanic)
	lockInit(&allglock, lockRankAllg)
	lockInit(&allpLock, lockRankAllp)
	lockInit(&reflectOffs.lock, lockRankReflectOffs)
	lockInit(&finlock, lockRankFin)
	lockInit(&trace.bufLock, lockRankTraceBuf)
	lockInit(&trace.stringsLock, lockRankTraceStrings)
	lockInit(&trace.lock, lockRankTrace)
	lockInit(&cpuprof.lock, lockRankCpuprof)
	lockInit(&trace.stackTab.lock, lockRankTraceStackTab)
	// Enforce that this lock is always a leaf lock.
	// All of this lock's critical sections should be
	// extremely short.
	lockInit(&memstats.heapStats.noPLock, lockRankLeafRank)

	// raceinit must be the first call to race detector.
	// In particular, it must be done before mallocinit below calls racemapshadow.
	_g_ := getg()
	if raceenabled {
		_g_.racectx, raceprocctx0 = raceinit()
	}

	sched.maxmcount = 10000 // 限制最大系统线程数量

	// The world starts stopped.
	worldStopped()

	moduledataverify()
	stackinit()  // 栈初始化
	mallocinit() // 内存分配器初始化
	cpuinit()      // must run before alginit
	alginit()      // maps, hash, fastrand must not be used before this call
	fastrandinit() // must run before mcommoninit
	mcommoninit(_g_.m, -1)
	modulesinit()   // provides activeModules
	typelinksinit() // uses maps, activeModules
	itabsinit()     // uses activeModules
	stkobjinit()    // must run before GC starts

	sigsave(&_g_.m.sigmask)
	initSigmask = _g_.m.sigmask

	if offset := unsafe.Offsetof(sched.timeToRun); offset%8 != 0 {
		println(offset)
		throw("sched.timeToRun not aligned to 8 bytes")
	}

	goargs()
	goenvs()
	parsedebugvars()
	gcinit()    // 垃圾回收器初始化

	lock(&sched.lock)
	sched.lastpoll = uint64(nanotime())
	
	// 创建 P
    // 通过 CPU 核心数和 GOMAXPROCS 环境变量确定 P 的数量
	procs := ncpu
	if n, ok := atoi32(gogetenv("GOMAXPROCS")); ok && n > 0 {
		procs = n
	}
	if procresize(procs) != nil {
		throw("unknown runnable goroutine during bootstrap")
	}
	unlock(&sched.lock)

	// World is effectively started now, as P's can run.
	worldStarted()

	// For cgocheck > 1, we turn on the write barrier at all times
	// and check all pointer writes. We can't do this until after
	// procresize because the write barrier needs a P.
	if debug.cgocheck > 1 {
		writeBarrier.cgo = true
		writeBarrier.enabled = true
		for _, p := range allp {
			p.wbBuf.reset()
		}
	}

	if buildVersion == "" {
		// Condition should never trigger. This code just serves
		// to ensure runtime·buildVersion is kept in the resulting binary.
		buildVersion = "unknown"
	}
	if len(modinfo) == 1 {
		// Condition should never trigger. This code just serves
		// to ensure runtime·modinfo is kept in the resulting binary.
		modinfo = ""
	}
}

newproc 负责根据主 goroutine （即main）入口地址创建可被运行时调度的执行单元
msstart 开始启动调度器的调度循环

Go-基础篇-图解启动过程

启动过程

流程图概览

步骤解释

参考