netpoll_epoll.go

Documentation: runtime

     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  	"runtime/internal/atomic"
    11  	"runtime/internal/syscall"
    12  	"unsafe"
    13  )
    14  
    15  var (
    16  	epfd int32 = -1 // epoll descriptor
    17  
    18  	netpollBreakRd, netpollBreakWr uintptr // for netpollBreak
    19  
    20  	netpollWakeSig atomic.Uint32 // used to avoid duplicate calls of netpollBreak
    21  )
    22  
    23  func netpollinit() {
    24  	var errno uintptr
    25  	epfd, errno = syscall.EpollCreate1(syscall.EPOLL_CLOEXEC)
    26  	if errno != 0 {
    27  		println("runtime: epollcreate failed with", errno)
    28  		throw("runtime: netpollinit failed")
    29  	}
    30  	r, w, errpipe := nonblockingPipe()
    31  	if errpipe != 0 {
    32  		println("runtime: pipe failed with", -errpipe)
    33  		throw("runtime: pipe failed")
    34  	}
    35  	ev := syscall.EpollEvent{
    36  		Events: syscall.EPOLLIN,
    37  	}
    38  	*(**uintptr)(unsafe.Pointer(&ev.Data)) = &netpollBreakRd
    39  	errno = syscall.EpollCtl(epfd, syscall.EPOLL_CTL_ADD, r, &ev)
    40  	if errno != 0 {
    41  		println("runtime: epollctl failed with", errno)
    42  		throw("runtime: epollctl failed")
    43  	}
    44  	netpollBreakRd = uintptr(r)
    45  	netpollBreakWr = uintptr(w)
    46  }
    47  
    48  func netpollIsPollDescriptor(fd uintptr) bool {
    49  	return fd == uintptr(epfd) || fd == netpollBreakRd || fd == netpollBreakWr
    50  }
    51  
    52  func netpollopen(fd uintptr, pd *pollDesc) uintptr {
    53  	var ev syscall.EpollEvent
    54  	ev.Events = syscall.EPOLLIN | syscall.EPOLLOUT | syscall.EPOLLRDHUP | syscall.EPOLLET
    55  	tp := taggedPointerPack(unsafe.Pointer(pd), pd.fdseq.Load())
    56  	*(*taggedPointer)(unsafe.Pointer(&ev.Data)) = tp
    57  	return syscall.EpollCtl(epfd, syscall.EPOLL_CTL_ADD, int32(fd), &ev)
    58  }
    59  
    60  func netpollclose(fd uintptr) uintptr {
    61  	var ev syscall.EpollEvent
    62  	return syscall.EpollCtl(epfd, syscall.EPOLL_CTL_DEL, int32(fd), &ev)
    63  }
    64  
    65  func netpollarm(pd *pollDesc, mode int) {
    66  	throw("runtime: unused")
    67  }
    68  
    69  // netpollBreak interrupts an epollwait.
    70  func netpollBreak() {
    71  	// Failing to cas indicates there is an in-flight wakeup, so we're done here.
    72  	if !netpollWakeSig.CompareAndSwap(0, 1) {
    73  		return
    74  	}
    75  
    76  	for {
    77  		var b byte
    78  		n := write(netpollBreakWr, unsafe.Pointer(&b), 1)
    79  		if n == 1 {
    80  			break
    81  		}
    82  		if n == -_EINTR {
    83  			continue
    84  		}
    85  		if n == -_EAGAIN {
    86  			return
    87  		}
    88  		println("runtime: netpollBreak write failed with", -n)
    89  		throw("runtime: netpollBreak write failed")
    90  	}
    91  }
    92  
    93  // netpoll checks for ready network connections.
    94  // Returns list of goroutines that become runnable.
    95  // delay < 0: blocks indefinitely
    96  // delay == 0: does not block, just polls
    97  // delay > 0: block for up to that many nanoseconds
    98  func netpoll(delay int64) (gList, int32) {
    99  	if epfd == -1 {
   100  		return gList{}, 0
   101  	}
   102  	var waitms int32
   103  	if delay < 0 {
   104  		waitms = -1
   105  	} else if delay == 0 {
   106  		waitms = 0
   107  	} else if delay < 1e6 {
   108  		waitms = 1
   109  	} else if delay < 1e15 {
   110  		waitms = int32(delay / 1e6)
   111  	} else {
   112  		// An arbitrary cap on how long to wait for a timer.
   113  		// 1e9 ms == ~11.5 days.
   114  		waitms = 1e9
   115  	}
   116  	var events [128]syscall.EpollEvent
   117  retry:
   118  	n, errno := syscall.EpollWait(epfd, events[:], int32(len(events)), waitms)
   119  	if errno != 0 {
   120  		if errno != _EINTR {
   121  			println("runtime: epollwait on fd", epfd, "failed with", errno)
   122  			throw("runtime: netpoll failed")
   123  		}
   124  		// If a timed sleep was interrupted, just return to
   125  		// recalculate how long we should sleep now.
   126  		if waitms > 0 {
   127  			return gList{}, 0
   128  		}
   129  		goto retry
   130  	}
   131  	var toRun gList
   132  	delta := int32(0)
   133  	for i := int32(0); i < n; i++ {
   134  		ev := events[i]
   135  		if ev.Events == 0 {
   136  			continue
   137  		}
   138  
   139  		if *(**uintptr)(unsafe.Pointer(&ev.Data)) == &netpollBreakRd {
   140  			if ev.Events != syscall.EPOLLIN {
   141  				println("runtime: netpoll: break fd ready for", ev.Events)
   142  				throw("runtime: netpoll: break fd ready for something unexpected")
   143  			}
   144  			if delay != 0 {
   145  				// netpollBreak could be picked up by a
   146  				// nonblocking poll. Only read the byte
   147  				// if blocking.
   148  				var tmp [16]byte
   149  				read(int32(netpollBreakRd), noescape(unsafe.Pointer(&tmp[0])), int32(len(tmp)))
   150  				netpollWakeSig.Store(0)
   151  			}
   152  			continue
   153  		}
   154  
   155  		var mode int32
   156  		if ev.Events&(syscall.EPOLLIN|syscall.EPOLLRDHUP|syscall.EPOLLHUP|syscall.EPOLLERR) != 0 {
   157  			mode += 'r'
   158  		}
   159  		if ev.Events&(syscall.EPOLLOUT|syscall.EPOLLHUP|syscall.EPOLLERR) != 0 {
   160  			mode += 'w'
   161  		}
   162  		if mode != 0 {
   163  			tp := *(*taggedPointer)(unsafe.Pointer(&ev.Data))
   164  			pd := (*pollDesc)(tp.pointer())
   165  			tag := tp.tag()
   166  			if pd.fdseq.Load() == tag {
   167  				pd.setEventErr(ev.Events == syscall.EPOLLERR, tag)
   168  				delta += netpollready(&toRun, pd, mode)
   169  			}
   170  		}
   171  	}
   172  	return toRun, delta
   173  }
   174
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