golang schedule crash

golang 起超过100W的goroutine就会crash，这个算不算是个bug？

---

2036119xxxx
panic: inconsistent poll.fdMutex

goroutine 2041065 [running]:
internal/poll.(*fdMutex).rwlock(0xc420090050, 0xc517305500, 0x1089b36)
/usr/local/Cellar/go/1.10/libexec/src/internal/poll/fd_mutex.go:145 +0x13f
internal/poll.(*FD).writeLock(0xc420090050, 0x1, 0x10c1cee)
/usr/local/Cellar/go/1.10/libexec/src/internal/poll/fd_mutex.go:237 +0x32
internal/poll.(*FD).Write(0xc420090050, 0xc518138ee0, 0x7, 0x8, 0x0, 0x0, 0x0)
/usr/local/Cellar/go/1.10/libexec/src/internal/poll/fd_unix.go:243 +0x46
os.(*File).write(0xc42000c018, 0xc518138ee0, 0x7, 0x8, 0x0, 0x0, 0x0)
/usr/local/Cellar/go/1.10/libexec/src/os/file_unix.go:243 +0x4e
os.(*File).Write(0xc42000c018, 0xc518138ee0, 0x7, 0x8, 0x8, 0xc517a3bd50, 0x0)
/usr/local/Cellar/go/1.10/libexec/src/os/file.go:144 +0x6f
fmt.Fprint(0x10d2720, 0xc42000c018, 0xc5173057b8, 0x1, 0x1, 0x109ed40, 0x0, 0xc518138ed8)
/usr/local/Cellar/go/1.10/libexec/src/fmt/print.go:223 +0x8b
fmt.Print(0xc5173057b8, 0x1, 0x1, 0xc518138ed8, 0x0, 0x0)
/usr/local/Cellar/go/1.10/libexec/src/fmt/print.go:232 +0x57
main.test(0x1f24c1)
/Users/guanshuai/go/src/main.go:11 +0x81
created by main.main
/Users/guanshuai/go/src/main.go:19 +0x87
exit status 2

real 0m10.859s
user 0m29.635s
sys 0m10.859s
[guanshuai] src $

---

mac os

goroutine 15192446 [running]:
internal/poll.(*fdMutex).rwlock(0xc420080050, 0x1000000010bf000, 0x0)
	/usr/local/go/src/internal/poll/fd_mutex.go:145 +0x13f
internal/poll.(*FD).writeLock(0xc420080050, 0xc420034800, 0xc4ddd4cc40)
	/usr/local/go/src/internal/poll/fd_mutex.go:237 +0x32
internal/poll.(*FD).Write(0xc420080050, 0xc4ddcea480, 0x11, 0x20, 0x0, 0x0, 0x0)
	/usr/local/go/src/internal/poll/fd_unix.go:243 +0x46
os.(*File).write(0xc42000c018, 0xc4ddcea480, 0x11, 0x20, 0x10, 0x10, 0x11)
	/usr/local/go/src/os/file_unix.go:243 +0x4e
os.(*File).Write(0xc42000c018, 0xc4ddcea480, 0x11, 0x20, 0x8, 0xc4531795a0, 0x0)
	/usr/local/go/src/os/file.go:144 +0x6f
fmt.Fprintln(0x10d09a0, 0xc42000c018, 0xc4ddd7e7a8, 0x2, 0x2, 0x109d300, 0x0, 0xc4531795a0)
	/usr/local/go/src/fmt/print.go:255 +0x8b
fmt.Println(0xc4ddd7e7a8, 0x2, 0x2, 0xc4531795a0, 0x0, 0x0)
	/usr/local/go/src/fmt/print.go:264 +0x57

　　

// lock adds a reference to mu and locks mu.
// It reports whether mu is available for reading or writing.
func (mu *fdMutex) rwlock(read bool) bool {
   var mutexBit, mutexWait, mutexMask uint64
   var mutexSema *uint32
   if read {
      mutexBit = mutexRLock
      mutexWait = mutexRWait
      mutexMask = mutexRMask
      mutexSema = &mu.rsema
   } else {
      mutexBit = mutexWLock
      mutexWait = mutexWWait
      mutexMask = mutexWMask
      mutexSema = &mu.wsema
   }
   for {
      old := atomic.LoadUint64(&mu.state)
      if old&mutexClosed != 0 {
         return false
      }
      var new uint64
      if old&mutexBit == 0 {
         // Lock is free, acquire it.
         new = (old | mutexBit) + mutexRef
         if new&mutexRefMask == 0 {
            panic("inconsistent poll.fdMutex")
         }
      } else {
         // Wait for lock.
         new = old + mutexWait
         if new&mutexMask == 0 {
            panic("inconsistent poll.fdMutex")
         }
      }
      if atomic.CompareAndSwapUint64(&mu.state, old, new) {
         if old&mutexBit == 0 {
            return true
         }
         runtime_Semacquire(mutexSema)
         // The signaller has subtracted mutexWait.
      }
   }
}

　　

// 1 bit - lock for write operations.
// 20 bits - total number of references (read+write+misc).
// 20 bits - number of outstanding read waiters.
// 20 bits - number of outstanding write waiter

// fdMutex.state is organized as follows:
// 1 bit - whether FD is closed, if set all subsequent lock operations will fail.
// 1 bit - lock for read operations.
// 1 bit - lock for write operations.
// 20 bits - total number of references (read+write+misc).
// 20 bits - number of outstanding read waiters.
// 20 bits - number of outstanding write waiters.
const (
   mutexClosed  = 1 << 0
   mutexRLock   = 1 << 1
   mutexWLock   = 1 << 2
   mutexRef     = 1 << 3
   mutexRefMask = (1<<20 - 1) << 3
   mutexRWait   = 1 << 23
   mutexRMask   = (1<<20 - 1) << 23
   mutexWWait   = 1 << 43
   mutexWMask   = (1<<20 - 1) << 43
)

互斥的变量里面是64位的数值

1.bit 代表是否关闭

2bit 锁的类型是读

3bit 锁的类型是写

4bit 可以递增的单位数值

5bit-- （22位）   掩码   2**22 = 2 * 2 ** 20

>>> import math
>>> pow(2, 20)
1048576
>>>

　　在一个file 或者socket上最大的锁为1000000， 所以有人提交patch，提示更精细的panic

https://go-review.googlesource.com/c/go/+/119956

internal/poll: better panic message for lock overflow

const overflowMsg = "too many concurrent operations on a single file or socket (max 1000000)"