netpoll_epoll.go

     1  // Copyright 2013 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  //go:build linux
     6  
     7  package runtime
     8  
     9  import (
    10  	"internal/runtime/atomic"
    11  	"internal/runtime/syscall"
    12  	"unsafe"
    13  )
    14  
    15  var (
    16  	epfd           int32         = -1 // epoll descriptor
    17  	netpollEventFd uintptr            // eventfd for netpollBreak
    18  	netpollWakeSig atomic.Uint32      // used to avoid duplicate calls of netpollBreak
    19  )
    20  
    21  func netpollinit() {
    22  	var errno uintptr
    23  	epfd, errno = syscall.EpollCreate1(syscall.EPOLL_CLOEXEC)
    24  	if errno != 0 {
    25  		println("runtime: epollcreate failed with", errno)
    26  		throw("runtime: netpollinit failed")
    27  	}
    28  	efd, errno := syscall.Eventfd(0, syscall.EFD_CLOEXEC|syscall.EFD_NONBLOCK)
    29  	if errno != 0 {
    30  		println("runtime: eventfd failed with", -errno)
    31  		throw("runtime: eventfd failed")
    32  	}
    33  	ev := syscall.EpollEvent{
    34  		Events: syscall.EPOLLIN,
    35  	}
    36  	*(**uintptr)(unsafe.Pointer(&ev.Data)) = &netpollEventFd
    37  	errno = syscall.EpollCtl(epfd, syscall.EPOLL_CTL_ADD, efd, &ev)
    38  	if errno != 0 {
    39  		println("runtime: epollctl failed with", errno)
    40  		throw("runtime: epollctl failed")
    41  	}
    42  	netpollEventFd = uintptr(efd)
    43  }
    44  
    45  func netpollIsPollDescriptor(fd uintptr) bool {
    46  	return fd == uintptr(epfd) || fd == netpollEventFd
    47  }
    48  
    49  func netpollopen(fd uintptr, pd *pollDesc) uintptr {
    50  	var ev syscall.EpollEvent
    51  	ev.Events = syscall.EPOLLIN | syscall.EPOLLOUT | syscall.EPOLLRDHUP | syscall.EPOLLET
    52  	tp := taggedPointerPack(unsafe.Pointer(pd), pd.fdseq.Load())
    53  	*(*taggedPointer)(unsafe.Pointer(&ev.Data)) = tp
    54  	return syscall.EpollCtl(epfd, syscall.EPOLL_CTL_ADD, int32(fd), &ev)
    55  }
    56  
    57  func netpollclose(fd uintptr) uintptr {
    58  	var ev syscall.EpollEvent
    59  	return syscall.EpollCtl(epfd, syscall.EPOLL_CTL_DEL, int32(fd), &ev)
    60  }
    61  
    62  func netpollarm(pd *pollDesc, mode int) {
    63  	throw("runtime: unused")
    64  }
    65  
    66  // netpollBreak interrupts an epollwait.
    67  func netpollBreak() {
    68  	// Failing to cas indicates there is an in-flight wakeup, so we're done here.
    69  	if !netpollWakeSig.CompareAndSwap(0, 1) {
    70  		return
    71  	}
    72  
    73  	var one uint64 = 1
    74  	oneSize := int32(unsafe.Sizeof(one))
    75  	for {
    76  		n := write(netpollEventFd, noescape(unsafe.Pointer(&one)), oneSize)
    77  		if n == oneSize {
    78  			break
    79  		}
    80  		if n == -_EINTR {
    81  			continue
    82  		}
    83  		if n == -_EAGAIN {
    84  			return
    85  		}
    86  		println("runtime: netpollBreak write failed with", -n)
    87  		throw("runtime: netpollBreak write failed")
    88  	}
    89  }
    90  
    91  // netpoll checks for ready network connections.
    92  // Returns a list of goroutines that become runnable,
    93  // and a delta to add to netpollWaiters.
    94  // This must never return an empty list with a non-zero delta.
    95  //
    96  // delay < 0: blocks indefinitely
    97  // delay == 0: does not block, just polls
    98  // delay > 0: block for up to that many nanoseconds
    99  func netpoll(delay int64) (gList, int32) {
   100  	if epfd == -1 {
   101  		return gList{}, 0
   102  	}
   103  	var waitms int32
   104  	if delay < 0 {
   105  		waitms = -1
   106  	} else if delay == 0 {
   107  		waitms = 0
   108  	} else if delay < 1e6 {
   109  		waitms = 1
   110  	} else if delay < 1e15 {
   111  		waitms = int32(delay / 1e6)
   112  	} else {
   113  		// An arbitrary cap on how long to wait for a timer.
   114  		// 1e9 ms == ~11.5 days.
   115  		waitms = 1e9
   116  	}
   117  	var events [128]syscall.EpollEvent
   118  retry:
   119  	n, errno := syscall.EpollWait(epfd, events[:], int32(len(events)), waitms)
   120  	if errno != 0 {
   121  		if errno != _EINTR {
   122  			println("runtime: epollwait on fd", epfd, "failed with", errno)
   123  			throw("runtime: netpoll failed")
   124  		}
   125  		// If a timed sleep was interrupted, just return to
   126  		// recalculate how long we should sleep now.
   127  		if waitms > 0 {
   128  			return gList{}, 0
   129  		}
   130  		goto retry
   131  	}
   132  	var toRun gList
   133  	delta := int32(0)
   134  	for i := int32(0); i < n; i++ {
   135  		ev := events[i]
   136  		if ev.Events == 0 {
   137  			continue
   138  		}
   139  
   140  		if *(**uintptr)(unsafe.Pointer(&ev.Data)) == &netpollEventFd {
   141  			if ev.Events != syscall.EPOLLIN {
   142  				println("runtime: netpoll: eventfd ready for", ev.Events)
   143  				throw("runtime: netpoll: eventfd ready for something unexpected")
   144  			}
   145  			if delay != 0 {
   146  				// netpollBreak could be picked up by a
   147  				// nonblocking poll. Only read the 8-byte
   148  				// integer if blocking.
   149  				// Since EFD_SEMAPHORE was not specified,
   150  				// the eventfd counter will be reset to 0.
   151  				var one uint64
   152  				read(int32(netpollEventFd), noescape(unsafe.Pointer(&one)), int32(unsafe.Sizeof(one)))
   153  				netpollWakeSig.Store(0)
   154  			}
   155  			continue
   156  		}
   157  
   158  		var mode int32
   159  		if ev.Events&(syscall.EPOLLIN|syscall.EPOLLRDHUP|syscall.EPOLLHUP|syscall.EPOLLERR) != 0 {
   160  			mode += 'r'
   161  		}
   162  		if ev.Events&(syscall.EPOLLOUT|syscall.EPOLLHUP|syscall.EPOLLERR) != 0 {
   163  			mode += 'w'
   164  		}
   165  		if mode != 0 {
   166  			tp := *(*taggedPointer)(unsafe.Pointer(&ev.Data))
   167  			pd := (*pollDesc)(tp.pointer())
   168  			tag := tp.tag()
   169  			if pd.fdseq.Load() == tag {
   170  				pd.setEventErr(ev.Events == syscall.EPOLLERR, tag)
   171  				delta += netpollready(&toRun, pd, mode)
   172  			}
   173  		}
   174  	}
   175  	return toRun, delta
   176  }
   177
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