Source file src/runtime/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  	"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  	*(**pollDesc)(unsafe.Pointer(&ev.Data)) = pd
    56  	return syscall.EpollCtl(epfd, syscall.EPOLL_CTL_ADD, int32(fd), &ev)
    57  }
    58  
    59  func netpollclose(fd uintptr) uintptr {
    60  	var ev syscall.EpollEvent
    61  	return syscall.EpollCtl(epfd, syscall.EPOLL_CTL_DEL, int32(fd), &ev)
    62  }
    63  
    64  func netpollarm(pd *pollDesc, mode int) {
    65  	throw("runtime: unused")
    66  }
    67  
    68  // netpollBreak interrupts an epollwait.
    69  func netpollBreak() {
    70  	// Failing to cas indicates there is an in-flight wakeup, so we're done here.
    71  	if !netpollWakeSig.CompareAndSwap(0, 1) {
    72  		return
    73  	}
    74  
    75  	for {
    76  		var b byte
    77  		n := write(netpollBreakWr, unsafe.Pointer(&b), 1)
    78  		if n == 1 {
    79  			break
    80  		}
    81  		if n == -_EINTR {
    82  			continue
    83  		}
    84  		if n == -_EAGAIN {
    85  			return
    86  		}
    87  		println("runtime: netpollBreak write failed with", -n)
    88  		throw("runtime: netpollBreak write failed")
    89  	}
    90  }
    91  
    92  // netpoll checks for ready network connections.
    93  // Returns list of goroutines that become runnable.
    94  // delay < 0: blocks indefinitely
    95  // delay == 0: does not block, just polls
    96  // delay > 0: block for up to that many nanoseconds
    97  func netpoll(delay int64) gList {
    98  	if epfd == -1 {
    99  		return gList{}
   100  	}
   101  	var waitms int32
   102  	if delay < 0 {
   103  		waitms = -1
   104  	} else if delay == 0 {
   105  		waitms = 0
   106  	} else if delay < 1e6 {
   107  		waitms = 1
   108  	} else if delay < 1e15 {
   109  		waitms = int32(delay / 1e6)
   110  	} else {
   111  		// An arbitrary cap on how long to wait for a timer.
   112  		// 1e9 ms == ~11.5 days.
   113  		waitms = 1e9
   114  	}
   115  	var events [128]syscall.EpollEvent
   116  retry:
   117  	n, errno := syscall.EpollWait(epfd, events[:], int32(len(events)), waitms)
   118  	if errno != 0 {
   119  		if errno != _EINTR {
   120  			println("runtime: epollwait on fd", epfd, "failed with", errno)
   121  			throw("runtime: netpoll failed")
   122  		}
   123  		// If a timed sleep was interrupted, just return to
   124  		// recalculate how long we should sleep now.
   125  		if waitms > 0 {
   126  			return gList{}
   127  		}
   128  		goto retry
   129  	}
   130  	var toRun gList
   131  	for i := int32(0); i < n; i++ {
   132  		ev := events[i]
   133  		if ev.Events == 0 {
   134  			continue
   135  		}
   136  
   137  		if *(**uintptr)(unsafe.Pointer(&ev.Data)) == &netpollBreakRd {
   138  			if ev.Events != syscall.EPOLLIN {
   139  				println("runtime: netpoll: break fd ready for", ev.Events)
   140  				throw("runtime: netpoll: break fd ready for something unexpected")
   141  			}
   142  			if delay != 0 {
   143  				// netpollBreak could be picked up by a
   144  				// nonblocking poll. Only read the byte
   145  				// if blocking.
   146  				var tmp [16]byte
   147  				read(int32(netpollBreakRd), noescape(unsafe.Pointer(&tmp[0])), int32(len(tmp)))
   148  				netpollWakeSig.Store(0)
   149  			}
   150  			continue
   151  		}
   152  
   153  		var mode int32
   154  		if ev.Events&(syscall.EPOLLIN|syscall.EPOLLRDHUP|syscall.EPOLLHUP|syscall.EPOLLERR) != 0 {
   155  			mode += 'r'
   156  		}
   157  		if ev.Events&(syscall.EPOLLOUT|syscall.EPOLLHUP|syscall.EPOLLERR) != 0 {
   158  			mode += 'w'
   159  		}
   160  		if mode != 0 {
   161  			pd := *(**pollDesc)(unsafe.Pointer(&ev.Data))
   162  			pd.setEventErr(ev.Events == syscall.EPOLLERR)
   163  			netpollready(&toRun, pd, mode)
   164  		}
   165  	}
   166  	return toRun
   167  }
   168  

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