Go 语言的 MPG 并发调度模型

type g struct {
	stack       stack
	stackguard0 uintptr
}

type stack struct {
	lo uintptr
	hi uintptr
}

type g struct {
  sched gobuf
}

type g struct {
  sched gobuf
}

type gobuf struct {
	sp   uintptr     // CPU 的 rsp 寄存器的值
	pc   uintptr     // CPU 的 rip 寄存器的值
	g    guintptr    // 记录当前的 gobuf 属于哪个 goroutine
	ret  sys.Uintreg // 保存系统调用的返回值
	bp   uintptr     // 记录 CPU 的 rbp 寄存器的值
}

type g struct {
	_panic       *_panic // 最内侧的 panic 结构体
	_defer       *_defer // 最内侧的延迟函数结构体
}

type g struct {
	m    *m
}

type g struct {
	atomicstatus uint32
}

type m struct {
	g0   *g  // goroutine with scheduling stack
}

type m struct {
	curg *g  // current running goroutine
}

type m struct {
	tls [6]uintptr // thread-local storage (for x86 extern register)
}

type m struct {
	p             puintptr
	nextp         puintptr
	oldp          puintptr
}

type p struct {
	runqhead uint32
	runqtail uint32
	runq     [256]guintptr
	runnext  guintptr
}

type p struct {
  m muintptr
}

type p struct {
	status      uint32
}

type schedt struct {
	lock mutex

	midle        muintptr // idle m's waiting for work
	nmidle       int32    // number of idle m's waiting for work
	nmidlelocked int32    // number of locked m's waiting for work
	mnext        int64    // number of m's that have been created and next M ID
	maxmcount    int32    // maximum number of m's allowed (or die)
	nmsys        int32    // number of system m's not counted for deadlock
	nmfreed      int64    // cumulative number of freed m's

	ngsys uint32 // number of system goroutines; updated atomically

	pidle      puintptr // idle p's
	npidle     uint32

	// Global runnable queue.
	runq     gQueue
	runqsize int32

	// Global cache of dead G's.
	gFree struct {
		lock    mutex
		stack   gList // Gs with stacks
		noStack gList // Gs without stacks
		n       int32
	}
  
	// freem is the list of m's waiting to be freed when their
	// m.exited is set. Linked through m.freelink.
	freem *m
}

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

	sched.maxmcount = 10000

	// The world starts stopped.
	worldStopped()

	moduledataverify()
	stackinit()
	mallocinit()
	fastrandinit() // must run before mcommoninit
	mcommoninit(_g_.m, -1)
	cpuinit()       // must run before alginit
	alginit()       // maps must not be used before this call
	modulesinit()   // provides activeModules
	typelinksinit() // uses maps, activeModules
	itabsinit()     // uses activeModules

	sigsave(&_g_.m.sigmask)

	goargs()
	goenvs()
	parsedebugvars()
	gcinit()

	lock(&sched.lock)
	sched.lastpoll = uint64(nanotime())
	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()
}

func procresize(nprocs int32) *p {
	assertLockHeld(&sched.lock)
	assertWorldStopped()

	old := gomaxprocs
	maskWords := (nprocs + 31) / 32

	// initialize new P's
	for i := old; i < nprocs; i++ {
		pp := allp[i]
		if pp == nil {
			pp = new(p)
		}
		pp.init(i)
		atomicstorep(unsafe.Pointer(&allp[i]), unsafe.Pointer(pp))
	}
	_g_ := getg()
	// g.m.p is now set, so we no longer need mcache0 for bootstrapping.
	mcache0 = nil
	// release resources from unused P's
	for i := nprocs; i < old; i++ {
		p := allp[i]
		p.destroy()
		// can't free P itself because it can be referenced by an M in syscall
	}
	var runnablePs *p
	var int32p *int32 = &gomaxprocs // make compiler check that gomaxprocs is an int32
	atomic.Store((*uint32)(unsafe.Pointer(int32p)), uint32(nprocs))
	return runnablePs
}

func newproc(siz int32, fn *funcval) {
	argp := add(unsafe.Pointer(&fn), sys.PtrSize)
	gp := getg()
	pc := getcallerpc()
	systemstack(func() {
		newg := newproc1(fn, argp, siz, gp, pc)

		_p_ := getg().m.p.ptr()
		runqput(_p_, newg, true)

		if mainStarted {
			wakep()
		}
	})
}

func newproc1(fn *funcval, argp unsafe.Pointer, narg int32, callergp *g, callerpc uintptr) *g {
	_g_ := getg()

	acquirem() // disable preemption because it can be holding p in a local var

	_p_ := _g_.m.p.ptr()
	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 isSystemGoroutine(newg, false) {
		atomic.Xadd(&sched.ngsys, +1)
	}
	casgstatus(newg, _Gdead, _Grunnable)
	releasem(_g_.m)

	return newg
}

func runqput(_p_ *p, gp *g, next bool) {
	if next {
	retryNext:
		oldnext := _p_.runnext
		if !_p_.runnext.cas(oldnext, guintptr(unsafe.Pointer(gp))) {
			goto retryNext
		}
		if oldnext == 0 {
			return
		}
		// Kick the old runnext out to the regular run queue.
		gp = oldnext.ptr()
	}

retry:
	h := atomic.LoadAcq(&_p_.runqhead) // load-acquire, synchronize with consumers
	t := _p_.runqtail
	if t-h < uint32(len(_p_.runq)) {
		_p_.runq[t%uint32(len(_p_.runq))].set(gp)
		atomic.StoreRel(&_p_.runqtail, t+1) // store-release, makes the item available for consumption
		return
	}
	if runqputslow(_p_, gp, h, t) {
		return
	}
	// the queue is not full, now the put above must succeed
	goto retry
}

func schedule() {
	_g_ := getg()

top:
	var gp *g
	var inheritTime bool

	if sched.disable.user && !schedEnabled(gp) {
		// Scheduling of this goroutine is disabled. Put it on
		// the list of pending runnable goroutines for when we
		// re-enable user scheduling and look again.
		lock(&sched.lock)
		if schedEnabled(gp) {
			// Something re-enabled scheduling while we
			// were acquiring the lock.
			unlock(&sched.lock)
		} else {
			sched.disable.runnable.pushBack(gp)
			sched.disable.n++
			unlock(&sched.lock)
			goto top
		}
	}

	execute(gp, inheritTime)
}

func execute(gp *g, inheritTime bool) {
	_g_ := getg()

	// Assign gp.m before entering _Grunning so running Gs have an
	// M.
	_g_.m.curg = gp
	gp.m = _g_.m
	casgstatus(gp, _Grunnable, _Grunning)
	gp.waitsince = 0
	gp.preempt = false
	gp.stackguard0 = gp.stack.lo + _StackGuard
	if !inheritTime {
		_g_.m.p.ptr().schedtick++
	}

	// Check whether the profiler needs to be turned on or off.
	hz := sched.profilehz
	if _g_.m.profilehz != hz {
		setThreadCPUProfiler(hz)
	}

	if trace.enabled {
		// GoSysExit has to happen when we have a P, but before GoStart.
		// So we emit it here.
		if gp.syscallsp != 0 && gp.sysblocktraced {
			traceGoSysExit(gp.sysexitticks)
		}
		traceGoStart()
	}

	gogo(&gp.sched)
}