golang源码

type m struct {
	/*
        1.  所有调用栈的Goroutine,这是一个比较特殊的Goroutine。
        2.  普通的Goroutine栈是在Heap分配的可增长的stack,而g0的stack是M对应的线程栈。
        3.  所有与调度相关的代码,都会先切换到g0的栈再执行。
    */
	g0      *g     // goroutine with scheduling stack
	morebuf gobuf  // gobuf arg to morestack
	divmod  uint32 // div/mod denominator for arm - known to liblink

	// Fields not known to debuggers.
	procid        uint64       // for debuggers, but offset not hard-coded
	gsignal       *g           // signal-handling g
	goSigStack    gsignalStack // Go-allocated signal handling stack
	sigmask       sigset       // storage for saved signal mask
	tls           [6]uintptr   // thread-local storage (for x86 extern register)
	// 表示M的起始函数。其实就是我们 go 语句携带的那个函数。
	mstartfn      func()
	// M中当前运行的goroutine
	curg          *g       // current running goroutine
	caughtsig     guintptr // goroutine running during fatal signal
	// 与M绑定的P，如果为nil表示空闲
	p             puintptr // attached p for executing go code (nil if not executing go code)
	// 用于暂存于当前M有潜在关联的P。 （预联）当M重新启动时，即用预联的这个P做关联啦
	nextp         puintptr
	id            int64
	mallocing     int32
	throwing      int32
	// 当前m是否关闭抢占式调度
	preemptoff    string // if != "", keep curg running on this m
	/**  */
	locks         int32
	dying         int32
	profilehz     int32
	// 不为0表示此m在做帮忙gc。helpgc等于n只是一个编号
	helpgc        int32
	// 自旋状态，表示当前M是否正在自旋寻找G。在寻找过程中M处于自旋状态。
	spinning      bool // m is out of work and is actively looking for work
	blocked       bool // m is blocked on a note
	inwb          bool // m is executing a write barrier
	newSigstack   bool // minit on C thread called sigaltstack
	printlock     int8
	incgo         bool   // m is executing a cgo call
	freeWait      uint32 // if == 0, safe to free g0 and delete m (atomic)
	fastrand      [2]uint32
	needextram    bool
	traceback     uint8
	ncgocall      uint64      // number of cgo calls in total
	ncgo          int32       // number of cgo calls currently in progress
	cgoCallersUse uint32      // if non-zero, cgoCallers in use temporarily
	cgoCallers    *cgoCallers // cgo traceback if crashing in cgo call
	park          note
	//这个域用于链接allm
	alllink       *m // on allm
	schedlink     muintptr
	mcache        *mcache
	// 表示与当前M锁定的那个G。运行时系统会把 一个M 和一个G锁定，一旦锁定就只能双方相互作用，不接受第三者。
	lockedg       guintptr
	createstack   [32]uintptr    // stack that created this thread.
	lockedExt     uint32         // tracking for external LockOSThread
	lockedInt     uint32         // tracking for internal lockOSThread
	nextwaitm     muintptr       // next m waiting for lock
	waitunlockf   unsafe.Pointer // todo go func(*g, unsafe.pointer) bool
	waitlock      unsafe.Pointer
	waittraceev   byte
	waittraceskip int
	startingtrace bool
	syscalltick   uint32
	thread        uintptr // thread handle
	freelink      *m      // on sched.freem

	// these are here because they are too large to be on the stack
	// of low-level NOSPLIT functions.
	libcall   libcall
	libcallpc uintptr // for cpu profiler
	libcallsp uintptr
	libcallg  guintptr
	syscall   libcall // stores syscall parameters on windows

	vdsoSP uintptr // SP for traceback while in VDSO call (0 if not in call)
	vdsoPC uintptr // PC for traceback while in VDSO call

	mOS
}