从计算机底层深入Golang高并发

从计算机底层深入Golang高并发

1.源码流程架构图

2.源码解读

runtime/proc.go下的newpro()

func newproc(fn *funcval) {
   //计算额外参数的地址argp
   gp := getg()
   pc := getcallerpc()
   //s1使用systemstack调用newproc1 
   systemstack(func() {
      newg := newproc1(fn, gp, pc)

      _p_ := getg().m.p.ptr()
      //s1将放到运行队列 
      runqput(_p_, newg, true)
      //s1 主是否启动，是否唤醒
      if mainStarted {
         wakep()
      }
   })
}

func newproc1(fn *funcval, callergp *g, callerpc uintptr) *g {
    //调用getg获取当前的g，会编译为讯取FS寄存器（TLS),这里会获到g
	_g_ := getg()

	if fn == nil {
		_g_.m.throwing = -1 // do not dump full stacks
		throw("go of nil func value")
	}
    //禁用抢咪，因为它可以在本地var中保存p,进入可见 设g对应的m的locks++
	acquirem() // disable preemption because it can be holding p in a local var

    //获取m拥有的p
	_p_ := _g_.m.p.ptr()
    //新建一个g
	newg := gfget(_p_)
	if newg == nil {
		newg = malg(_StackMin)
		casgstatus(newg, _Gidle, _Gdead)
		allgadd(newg) // publishes with a g->status of Gdead so GC scanner doesn't look at uninitialized stack.
	}
	if newg.stack.hi == 0 {
		throw("newproc1: newg missing stack")
	}

	if readgstatus(newg) != _Gdead {
		throw("newproc1: new g is not Gdead")
	}

	totalSize := uintptr(4*goarch.PtrSize + sys.MinFrameSize) // extra space in case of reads slightly beyond frame
	totalSize = alignUp(totalSize, sys.StackAlign)
	sp := newg.stack.hi - totalSize
	spArg := sp
	if usesLR {
		// caller's LR
		*(*uintptr)(unsafe.Pointer(sp)) = 0
		prepGoExitFrame(sp)
		spArg += sys.MinFrameSize
	}
	
    //设置g的调度
	memclrNoHeapPointers(unsafe.Pointer(&newg.sched), unsafe.Sizeof(newg.sched))
	newg.sched.sp = sp
	newg.stktopsp = sp
	newg.sched.pc = abi.FuncPCABI0(goexit) + sys.PCQuantum // +PCQuantum so that previous instruction is in same function
	newg.sched.g = guintptr(unsafe.Pointer(newg))
	gostartcallfn(&newg.sched, fn)
	newg.gopc = callerpc
	newg.ancestors = saveAncestors(callergp)
	newg.startpc = fn.fn
	if isSystemGoroutine(newg, false) {
		atomic.Xadd(&sched.ngsys, +1)
	} else {
		// Only user goroutines inherit pprof labels.
		if _g_.m.curg != nil {
			newg.labels = _g_.m.curg.labels
		}
	}
	// Track initial transition?
	newg.trackingSeq = uint8(fastrand())
	if newg.trackingSeq%gTrackingPeriod == 0 {
		newg.tracking = true
	}
    //设置g的状态为待运行
	casgstatus(newg, _Gdead, _Grunnable)
	gcController.addScannableStack(_p_, int64(newg.stack.hi-newg.stack.lo))

	if _p_.goidcache == _p_.goidcacheend {
		// Sched.goidgen is the last allocated id,
		// this batch must be [sched.goidgen+1, sched.goidgen+GoidCacheBatch].
		// At startup sched.goidgen=0, so main goroutine receives goid=1.
		_p_.goidcache = atomic.Xadd64(&sched.goidgen, _GoidCacheBatch)
		_p_.goidcache -= _GoidCacheBatch - 1
		_p_.goidcacheend = _p_.goidcache + _GoidCacheBatch
	}
	newg.goid = int64(_p_.goidcache)
	_p_.goidcache++
	if raceenabled {
		newg.racectx = racegostart(callerpc)
	}
	if trace.enabled {
		traceGoCreate(newg, newg.startpc)
	}
	releasem(_g_.m)

	return newg
}

func main() {
	g := getg() //获取g

	// Racectx of m0->g0 is used only as the parent of the main goroutine.
	// It must not be used for anything else.
	g.m.g0.racectx = 0

	// Max stack size is 1 GB on 64-bit, 250 MB on 32-bit.
	// Using decimal instead of binary GB and MB because
	// they look nicer in the stack overflow failure message.
	if goarch.PtrSize == 8 {
		maxstacksize = 1000000000
	} else {
		maxstacksize = 250000000
	}

	// An upper limit for max stack size. Used to avoid random crashes
	// after calling SetMaxStack and trying to allocate a stack that is too big,
	// since stackalloc works with 32-bit sizes.
	maxstackceiling = 2 * maxstacksize

	// 标记主函数已调用.
    mainStarted = true
	//判断是否已就绪
	if GOARCH != "wasm" { // no threads on wasm yet, so no sysmon
		systemstack(func() {
			newm(sysmon, nil, -1)
		})
	}

	// Lock the main goroutine onto this, the main OS thread,
	// during initialization. Most programs won't care, but a few
	// do require certain calls to be made by the main thread.
	// Those can arrange for main.main to run in the main thread
	// by calling runtime.LockOSThread during initialization
	// to preserve the lock.
	lockOSThread()

	if g.m != &m0 {
		throw("runtime.main not on m0")
	}

	// Record when the world started.
	// Must be before doInit for tracing init.
	runtimeInitTime = nanotime()
	if runtimeInitTime == 0 {
		throw("nanotime returning zero")
	}

	if debug.inittrace != 0 {
		inittrace.id = getg().goid
		inittrace.active = true
	}
	//初始化
	doInit(&runtime_inittask) // Must be before defer.

	// Defer unlock so that runtime.Goexit during init does the unlock too.
	needUnlock := true
	defer func() {
		if needUnlock {
			unlockOSThread()
		}
	}()

	gcenable()

	main_init_done = make(chan bool)
	if iscgo {
		if _cgo_thread_start == nil {
			throw("_cgo_thread_start missing")
		}
		if GOOS != "windows" {
			if _cgo_setenv == nil {
				throw("_cgo_setenv missing")
			}
			if _cgo_unsetenv == nil {
				throw("_cgo_unsetenv missing")
			}
		}
		if _cgo_notify_runtime_init_done == nil {
			throw("_cgo_notify_runtime_init_done missing")
		}
		// Start the template thread in case we enter Go from
		// a C-created thread and need to create a new thread.
		startTemplateThread()
		cgocall(_cgo_notify_runtime_init_done, nil)
	}

	doInit(&main_inittask)

	// Disable init tracing after main init done to avoid overhead
	// of collecting statistics in malloc and newproc
	inittrace.active = false

	close(main_init_done)

	needUnlock = false
	unlockOSThread()

	if isarchive || islibrary {
		// A program compiled with -buildmode=c-archive or c-shared
		// has a main, but it is not executed.
		return
	}
    //进行间接调用
	fn := main_main // make an indirect call, as the linker doesn't know the address of the main package when laying down the runtime
	fn()
	if raceenabled {
		racefini()
	}

	// Make racy client program work: if panicking on
	// another goroutine at the same time as main returns,
	// let the other goroutine finish printing the panic trace.
	// Once it does, it will exit. See issues 3934 and 20018.
	if atomic.Load(&runningPanicDefers) != 0 {
		// Running deferred functions should not take long.
		for c := 0; c < 1000; c++ {
			if atomic.Load(&runningPanicDefers) == 0 {
				break
			}
			Gosched()
		}
	}
	if atomic.Load(&panicking) != 0 {
		gopark(nil, nil, waitReasonPanicWait, traceEvGoStop, 1)
	}

	exit(0)
	for {
		var x *int32
		*x = 0
	}
}

func sysmon() {
	lock(&sched.lock)
	sched.nmsys++
	checkdead()
	unlock(&sched.lock)

	lasttrace := int64(0)
	idle := 0 // how many cycles in succession we had not wokeup somebody
	delay := uint32(0)

	for {
		if idle == 0 { // start with 20us sleep...
			delay = 20
		} else if idle > 50 { // start doubling the sleep after 1ms...
			delay *= 2
		}
		if delay > 10*1000 { // up to 10ms
			delay = 10 * 1000
		}
		usleep(delay)

		// sysmon should not enter deep sleep if schedtrace is enabled so that
		// it can print that information at the right time.
		//
		// It should also not enter deep sleep if there are any active P's so
		// that it can retake P's from syscalls, preempt long running G's, and
		// poll the network if all P's are busy for long stretches.
		//
		// It should wakeup from deep sleep if any P's become active either due
		// to exiting a syscall or waking up due to a timer expiring so that it
		// can resume performing those duties. If it wakes from a syscall it
		// resets idle and delay as a bet that since it had retaken a P from a
		// syscall before, it may need to do it again shortly after the
		// application starts work again. It does not reset idle when waking
		// from a timer to avoid adding system load to applications that spend
		// most of their time sleeping.
		now := nanotime()
		if debug.schedtrace <= 0 && (sched.gcwaiting != 0 || atomic.Load(&sched.npidle) == uint32(gomaxprocs)) {
			lock(&sched.lock)
			if atomic.Load(&sched.gcwaiting) != 0 || atomic.Load(&sched.npidle) == uint32(gomaxprocs) {
				syscallWake := false
				next, _ := timeSleepUntil()
				if next > now {
					atomic.Store(&sched.sysmonwait, 1)
					unlock(&sched.lock)
					// Make wake-up period small enough
					// for the sampling to be correct.
					sleep := forcegcperiod / 2
					if next-now < sleep {
						sleep = next - now
					}
					shouldRelax := sleep >= osRelaxMinNS
					if shouldRelax {
						osRelax(true)
					}
					syscallWake = notetsleep(&sched.sysmonnote, sleep)
					if shouldRelax {
						osRelax(false)
					}
					lock(&sched.lock)
					atomic.Store(&sched.sysmonwait, 0)
					noteclear(&sched.sysmonnote)
				}
				if syscallWake {
					idle = 0
					delay = 20
				}
			}
			unlock(&sched.lock)
		}

		lock(&sched.sysmonlock)
		// Update now in case we blocked on sysmonnote or spent a long time
		// blocked on schedlock or sysmonlock above.
		now = nanotime()

		// trigger libc interceptors if needed
		if *cgo_yield != nil {
			asmcgocall(*cgo_yield, nil)
		}
		// poll network if not polled for more than 10ms
		lastpoll := int64(atomic.Load64(&sched.lastpoll))
		if netpollinited() && lastpoll != 0 && lastpoll+10*1000*1000 < now {
			atomic.Cas64(&sched.lastpoll, uint64(lastpoll), uint64(now))
			list := netpoll(0) // non-blocking - returns list of goroutines
			if !list.empty() {
				// Need to decrement number of idle locked M's
				// (pretending that one more is running) before injectglist.
				// Otherwise it can lead to the following situation:
				// injectglist grabs all P's but before it starts M's to run the P's,
				// another M returns from syscall, finishes running its G,
				// observes that there is no work to do and no other running M's
				// and reports deadlock.
				incidlelocked(-1)
				injectglist(&list)
				incidlelocked(1)
			}
		}
		if GOOS == "netbsd" && needSysmonWorkaround {
			// netpoll is responsible for waiting for timer
			// expiration, so we typically don't have to worry
			// about starting an M to service timers. (Note that
			// sleep for timeSleepUntil above simply ensures sysmon
			// starts running again when that timer expiration may
			// cause Go code to run again).
			//
			// However, netbsd has a kernel bug that sometimes
			// misses netpollBreak wake-ups, which can lead to
			// unbounded delays servicing timers. If we detect this
			// overrun, then startm to get something to handle the
			// timer.
			//
			// See issue 42515 and
			// https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=50094.
			if next, _ := timeSleepUntil(); next < now {
				startm(nil, false)
			}
		}
		if atomic.Load(&scavenge.sysmonWake) != 0 {
			// Kick the scavenger awake if someone requested it.
			wakeScavenger()
		}
		 // S1重新获取系统调用中阻塞的P，点长时间运行的G
		if retake(now) != 0 {
			idle = 0
		} else {
			idle++
		}
		// check if we need to force a GC
		if t := (gcTrigger{kind: gcTriggerTime, now: now}); t.test() && atomic.Load(&forcegc.idle) != 0 {
			lock(&forcegc.lock)
			forcegc.idle = 0
			var list gList
			list.push(forcegc.g)
			injectglist(&list)
			unlock(&forcegc.lock)
		}
		if debug.schedtrace > 0 && lasttrace+int64(debug.schedtrace)*1000000 <= now {
			lasttrace = now
			schedtrace(debug.scheddetail > 0)
		}
		unlock(&sched.sysmonlock)
	}
}

func retake(now int64) uint32 {
	n := 0
	// Prevent allp slice changes. This lock will be completely
	// uncontended unless we're already stopping the world.
	lock(&allpLock)
	// We can't use a range loop over allp because we may
	// temporarily drop the allpLock. Hence, we need to re-fetch
	// allp each time around the loop.
	for i := 0; i < len(allp); i++ {
		_p_ := allp[i]
		if _p_ == nil {
			// This can happen if procresize has grown
			// allp but not yet created new Ps.
			continue
		}
		pd := &_p_.sysmontick
		s := _p_.status
		sysretake := false
		if s == _Prunning || s == _Psyscall {
			// Preempt G if it's running for too long.
			t := int64(_p_.schedtick)
			if int64(pd.schedtick) != t {
				pd.schedtick = uint32(t)
				pd.schedwhen = now
			} else if pd.schedwhen+forcePreemptNS <= now {
				preemptone(_p_)
				// In case of syscall, preemptone() doesn't
				// work, because there is no M wired to P.
				sysretake = true
			}
		}
        //如果P在系统中调用( _Psyscall),且经历过了sysmon循环（20us-10ms)，则抢占这个P
		if s == _Psyscall {
			// Retake P from syscall if it's there for more than 1 sysmon tick (at least 20us).
			t := int64(_p_.syscalltick)
			if !sysretake && int64(pd.syscalltick) != t {
				pd.syscalltick = uint32(t)
				pd.syscallwhen = now
				continue
			}
			// On the one hand we don't want to retake Ps if there is no other work to do,
			// but on the other hand we want to retake them eventually
			// because they can prevent the sysmon thread from deep sleep.
            //如果当前P,Local队列没有其它G,当前有其它G处理Idle状态，并且syscall执行事件不超过10ms,则不用解绑当前P
			if runqempty(_p_) && atomic.Load(&sched.nmspinning)+atomic.Load(&sched.npidle) > 0 && pd.syscallwhen+10*1000*1000 > now {
				continue
			}
			// Drop allpLock so we can take sched.lock.
			unlock(&allpLock)
			// Need to decrement number of idle locked M's
			// (pretending that one more is running) before the CAS.
			// Otherwise the M from which we retake can exit the syscall,
			// increment nmidle and report deadlock.
			incidlelocked(-1)
			if atomic.Cas(&_p_.status, s, _Pidle) {
				if trace.enabled {
					traceGoSysBlock(_p_)
					traceProcStop(_p_)
				}
				n++
				_p_.syscalltick++
				handoffp(_p_)
			}
			incidlelocked(1)
			lock(&allpLock)
		}
	}
	unlock(&allpLock)
	return uint32(n)
}


func startm(_p_ *p, spinning bool) {
	// Disable preemption.
	//
	// Every owned P must have an owner that will eventually stop it in the
	// event of a GC stop request. startm takes transient ownership of a P
	// (either from argument or pidleget below) and transfers ownership to
	// a started M, which will be responsible for performing the stop.
	//
	// Preemption must be disabled during this transient ownership,
	// otherwise the P this is running on may enter GC stop while still
	// holding the transient P, leaving that P in limbo and deadlocking the
	// STW.
	//
	// Callers passing a non-nil P must already be in non-preemptible
	// context, otherwise such preemption could occur on function entry to
	// startm. Callers passing a nil P may be preemptible, so we must
	// disable preemption before acquiring a P from pidleget below.
	mp := acquirem()
	lock(&sched.lock)
	if _p_ == nil { //从"空闲P链表"获取一个空间的P
		_p_ = pidleget()
		if _p_ == nil {
			unlock(&sched.lock)
			if spinning {
				// The caller incremented nmspinning, but there are no idle Ps,
				// so it's okay to just undo the increment and give up.
				if int32(atomic.Xadd(&sched.nmspinning, -1)) < 0 {
					throw("startm: negative nmspinning")
				}
			}
			releasem(mp)
			return
		}
	} //
	nmp := mget() //从"空闲m链表"获取一个空间的m
    //如果没有空闲的m,则会创建一个
	if nmp == nil {
		// No M is available, we must drop sched.lock and call newm.
		// However, we already own a P to assign to the M.
		//
		// Once sched.lock is released, another G (e.g., in a syscall),
		// could find no idle P while checkdead finds a runnable G but
		// no running M's because this new M hasn't started yet, thus
		// throwing in an apparent deadlock.
		//
		// Avoid this situation by pre-allocating the ID for the new M,
		// thus marking it as 'running' before we drop sched.lock. This
		// new M will eventually run the scheduler to execute any
		// queued G's.
		id := mReserveID()
		unlock(&sched.lock)

		var fn func()
		if spinning {
			// The caller incremented nmspinning, so set m.spinning in the new M.
			fn = mspinning
		}
        //会新建一个的m实例，m的实例包含一个go,然后调用newsproc动一个系统线程
		newm(fn, _p_, id)
		// Ownership transfer of _p_ committed by start in newm.
		// Preemption is now safe.
		releasem(mp)
		return
	}
	unlock(&sched.lock)
	if nmp.spinning {
		throw("startm: m is spinning")
	}
	if nmp.nextp != 0 {
		throw("startm: m has p")
	}
	if spinning && !runqempty(_p_) {
		throw("startm: p has runnable gs")
	}
	// The caller incremented nmspinning, so set m.spinning in the new M.
	nmp.spinning = spinning
	nmp.nextp.set(_p_)
	notewakeup(&nmp.park)
	// Ownership transfer of _p_ committed by wakeup. Preemption is now
	// safe.
	releasem(mp)
}