netpoll.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 unix || (js && wasm) || wasip1 || windows
     6  
     7  package runtime
     8  
     9  import (
    10  	"runtime/internal/atomic"
    11  	"runtime/internal/sys"
    12  	"unsafe"
    13  )
    14  
    15  // Integrated network poller (platform-independent part).
    16  // A particular implementation (epoll/kqueue/port/AIX/Windows)
    17  // must define the following functions:
    18  //
    19  // func netpollinit()
    20  //     Initialize the poller. Only called once.
    21  //
    22  // func netpollopen(fd uintptr, pd *pollDesc) int32
    23  //     Arm edge-triggered notifications for fd. The pd argument is to pass
    24  //     back to netpollready when fd is ready. Return an errno value.
    25  //
    26  // func netpollclose(fd uintptr) int32
    27  //     Disable notifications for fd. Return an errno value.
    28  //
    29  // func netpoll(delta int64) gList
    30  //     Poll the network. If delta < 0, block indefinitely. If delta == 0,
    31  //     poll without blocking. If delta > 0, block for up to delta nanoseconds.
    32  //     Return a list of goroutines built by calling netpollready.
    33  //
    34  // func netpollBreak()
    35  //     Wake up the network poller, assumed to be blocked in netpoll.
    36  //
    37  // func netpollIsPollDescriptor(fd uintptr) bool
    38  //     Reports whether fd is a file descriptor used by the poller.
    39  
    40  // Error codes returned by runtime_pollReset and runtime_pollWait.
    41  // These must match the values in internal/poll/fd_poll_runtime.go.
    42  const (
    43  	pollNoError        = 0 // no error
    44  	pollErrClosing     = 1 // descriptor is closed
    45  	pollErrTimeout     = 2 // I/O timeout
    46  	pollErrNotPollable = 3 // general error polling descriptor
    47  )
    48  
    49  // pollDesc contains 2 binary semaphores, rg and wg, to park reader and writer
    50  // goroutines respectively. The semaphore can be in the following states:
    51  //
    52  //	pdReady - io readiness notification is pending;
    53  //	          a goroutine consumes the notification by changing the state to pdNil.
    54  //	pdWait - a goroutine prepares to park on the semaphore, but not yet parked;
    55  //	         the goroutine commits to park by changing the state to G pointer,
    56  //	         or, alternatively, concurrent io notification changes the state to pdReady,
    57  //	         or, alternatively, concurrent timeout/close changes the state to pdNil.
    58  //	G pointer - the goroutine is blocked on the semaphore;
    59  //	            io notification or timeout/close changes the state to pdReady or pdNil respectively
    60  //	            and unparks the goroutine.
    61  //	pdNil - none of the above.
    62  const (
    63  	pdNil   uintptr = 0
    64  	pdReady uintptr = 1
    65  	pdWait  uintptr = 2
    66  )
    67  
    68  const pollBlockSize = 4 * 1024
    69  
    70  // Network poller descriptor.
    71  //
    72  // No heap pointers.
    73  type pollDesc struct {
    74  	_     sys.NotInHeap
    75  	link  *pollDesc      // in pollcache, protected by pollcache.lock
    76  	fd    uintptr        // constant for pollDesc usage lifetime
    77  	fdseq atomic.Uintptr // protects against stale pollDesc
    78  
    79  	// atomicInfo holds bits from closing, rd, and wd,
    80  	// which are only ever written while holding the lock,
    81  	// summarized for use by netpollcheckerr,
    82  	// which cannot acquire the lock.
    83  	// After writing these fields under lock in a way that
    84  	// might change the summary, code must call publishInfo
    85  	// before releasing the lock.
    86  	// Code that changes fields and then calls netpollunblock
    87  	// (while still holding the lock) must call publishInfo
    88  	// before calling netpollunblock, because publishInfo is what
    89  	// stops netpollblock from blocking anew
    90  	// (by changing the result of netpollcheckerr).
    91  	// atomicInfo also holds the eventErr bit,
    92  	// recording whether a poll event on the fd got an error;
    93  	// atomicInfo is the only source of truth for that bit.
    94  	atomicInfo atomic.Uint32 // atomic pollInfo
    95  
    96  	// rg, wg are accessed atomically and hold g pointers.
    97  	// (Using atomic.Uintptr here is similar to using guintptr elsewhere.)
    98  	rg atomic.Uintptr // pdReady, pdWait, G waiting for read or pdNil
    99  	wg atomic.Uintptr // pdReady, pdWait, G waiting for write or pdNil
   100  
   101  	lock    mutex // protects the following fields
   102  	closing bool
   103  	user    uint32    // user settable cookie
   104  	rseq    uintptr   // protects from stale read timers
   105  	rt      timer     // read deadline timer (set if rt.f != nil)
   106  	rd      int64     // read deadline (a nanotime in the future, -1 when expired)
   107  	wseq    uintptr   // protects from stale write timers
   108  	wt      timer     // write deadline timer
   109  	wd      int64     // write deadline (a nanotime in the future, -1 when expired)
   110  	self    *pollDesc // storage for indirect interface. See (*pollDesc).makeArg.
   111  }
   112  
   113  // pollInfo is the bits needed by netpollcheckerr, stored atomically,
   114  // mostly duplicating state that is manipulated under lock in pollDesc.
   115  // The one exception is the pollEventErr bit, which is maintained only
   116  // in the pollInfo.
   117  type pollInfo uint32
   118  
   119  const (
   120  	pollClosing = 1 << iota
   121  	pollEventErr
   122  	pollExpiredReadDeadline
   123  	pollExpiredWriteDeadline
   124  	pollFDSeq // 20 bit field, low 20 bits of fdseq field
   125  )
   126  
   127  const (
   128  	pollFDSeqBits = 20                   // number of bits in pollFDSeq
   129  	pollFDSeqMask = 1<<pollFDSeqBits - 1 // mask for pollFDSeq
   130  )
   131  
   132  func (i pollInfo) closing() bool              { return i&pollClosing != 0 }
   133  func (i pollInfo) eventErr() bool             { return i&pollEventErr != 0 }
   134  func (i pollInfo) expiredReadDeadline() bool  { return i&pollExpiredReadDeadline != 0 }
   135  func (i pollInfo) expiredWriteDeadline() bool { return i&pollExpiredWriteDeadline != 0 }
   136  
   137  // info returns the pollInfo corresponding to pd.
   138  func (pd *pollDesc) info() pollInfo {
   139  	return pollInfo(pd.atomicInfo.Load())
   140  }
   141  
   142  // publishInfo updates pd.atomicInfo (returned by pd.info)
   143  // using the other values in pd.
   144  // It must be called while holding pd.lock,
   145  // and it must be called after changing anything
   146  // that might affect the info bits.
   147  // In practice this means after changing closing
   148  // or changing rd or wd from < 0 to >= 0.
   149  func (pd *pollDesc) publishInfo() {
   150  	var info uint32
   151  	if pd.closing {
   152  		info |= pollClosing
   153  	}
   154  	if pd.rd < 0 {
   155  		info |= pollExpiredReadDeadline
   156  	}
   157  	if pd.wd < 0 {
   158  		info |= pollExpiredWriteDeadline
   159  	}
   160  	info |= uint32(pd.fdseq.Load()&pollFDSeqMask) << pollFDSeq
   161  
   162  	// Set all of x except the pollEventErr bit.
   163  	x := pd.atomicInfo.Load()
   164  	for !pd.atomicInfo.CompareAndSwap(x, (x&pollEventErr)|info) {
   165  		x = pd.atomicInfo.Load()
   166  	}
   167  }
   168  
   169  // setEventErr sets the result of pd.info().eventErr() to b.
   170  // We only change the error bit if seq == 0 or if seq matches pollFDSeq
   171  // (issue #59545).
   172  func (pd *pollDesc) setEventErr(b bool, seq uintptr) {
   173  	mSeq := uint32(seq & pollFDSeqMask)
   174  	x := pd.atomicInfo.Load()
   175  	xSeq := (x >> pollFDSeq) & pollFDSeqMask
   176  	if seq != 0 && xSeq != mSeq {
   177  		return
   178  	}
   179  	for (x&pollEventErr != 0) != b && !pd.atomicInfo.CompareAndSwap(x, x^pollEventErr) {
   180  		x = pd.atomicInfo.Load()
   181  		xSeq := (x >> pollFDSeq) & pollFDSeqMask
   182  		if seq != 0 && xSeq != mSeq {
   183  			return
   184  		}
   185  	}
   186  }
   187  
   188  type pollCache struct {
   189  	lock  mutex
   190  	first *pollDesc
   191  	// PollDesc objects must be type-stable,
   192  	// because we can get ready notification from epoll/kqueue
   193  	// after the descriptor is closed/reused.
   194  	// Stale notifications are detected using seq variable,
   195  	// seq is incremented when deadlines are changed or descriptor is reused.
   196  }
   197  
   198  var (
   199  	netpollInitLock mutex
   200  	netpollInited   atomic.Uint32
   201  
   202  	pollcache      pollCache
   203  	netpollWaiters atomic.Uint32
   204  )
   205  
   206  //go:linkname poll_runtime_pollServerInit internal/poll.runtime_pollServerInit
   207  func poll_runtime_pollServerInit() {
   208  	netpollGenericInit()
   209  }
   210  
   211  func netpollGenericInit() {
   212  	if netpollInited.Load() == 0 {
   213  		lockInit(&netpollInitLock, lockRankNetpollInit)
   214  		lock(&netpollInitLock)
   215  		if netpollInited.Load() == 0 {
   216  			netpollinit()
   217  			netpollInited.Store(1)
   218  		}
   219  		unlock(&netpollInitLock)
   220  	}
   221  }
   222  
   223  func netpollinited() bool {
   224  	return netpollInited.Load() != 0
   225  }
   226  
   227  //go:linkname poll_runtime_isPollServerDescriptor internal/poll.runtime_isPollServerDescriptor
   228  
   229  // poll_runtime_isPollServerDescriptor reports whether fd is a
   230  // descriptor being used by netpoll.
   231  func poll_runtime_isPollServerDescriptor(fd uintptr) bool {
   232  	return netpollIsPollDescriptor(fd)
   233  }
   234  
   235  //go:linkname poll_runtime_pollOpen internal/poll.runtime_pollOpen
   236  func poll_runtime_pollOpen(fd uintptr) (*pollDesc, int) {
   237  	pd := pollcache.alloc()
   238  	lock(&pd.lock)
   239  	wg := pd.wg.Load()
   240  	if wg != pdNil && wg != pdReady {
   241  		throw("runtime: blocked write on free polldesc")
   242  	}
   243  	rg := pd.rg.Load()
   244  	if rg != pdNil && rg != pdReady {
   245  		throw("runtime: blocked read on free polldesc")
   246  	}
   247  	pd.fd = fd
   248  	if pd.fdseq.Load() == 0 {
   249  		// The value 0 is special in setEventErr, so don't use it.
   250  		pd.fdseq.Store(1)
   251  	}
   252  	pd.closing = false
   253  	pd.setEventErr(false, 0)
   254  	pd.rseq++
   255  	pd.rg.Store(pdNil)
   256  	pd.rd = 0
   257  	pd.wseq++
   258  	pd.wg.Store(pdNil)
   259  	pd.wd = 0
   260  	pd.self = pd
   261  	pd.publishInfo()
   262  	unlock(&pd.lock)
   263  
   264  	errno := netpollopen(fd, pd)
   265  	if errno != 0 {
   266  		pollcache.free(pd)
   267  		return nil, int(errno)
   268  	}
   269  	return pd, 0
   270  }
   271  
   272  //go:linkname poll_runtime_pollClose internal/poll.runtime_pollClose
   273  func poll_runtime_pollClose(pd *pollDesc) {
   274  	if !pd.closing {
   275  		throw("runtime: close polldesc w/o unblock")
   276  	}
   277  	wg := pd.wg.Load()
   278  	if wg != pdNil && wg != pdReady {
   279  		throw("runtime: blocked write on closing polldesc")
   280  	}
   281  	rg := pd.rg.Load()
   282  	if rg != pdNil && rg != pdReady {
   283  		throw("runtime: blocked read on closing polldesc")
   284  	}
   285  	netpollclose(pd.fd)
   286  	pollcache.free(pd)
   287  }
   288  
   289  func (c *pollCache) free(pd *pollDesc) {
   290  	// pd can't be shared here, but lock anyhow because
   291  	// that's what publishInfo documents.
   292  	lock(&pd.lock)
   293  
   294  	// Increment the fdseq field, so that any currently
   295  	// running netpoll calls will not mark pd as ready.
   296  	fdseq := pd.fdseq.Load()
   297  	fdseq = (fdseq + 1) & (1<<taggedPointerBits - 1)
   298  	pd.fdseq.Store(fdseq)
   299  
   300  	pd.publishInfo()
   301  
   302  	unlock(&pd.lock)
   303  
   304  	lock(&c.lock)
   305  	pd.link = c.first
   306  	c.first = pd
   307  	unlock(&c.lock)
   308  }
   309  
   310  // poll_runtime_pollReset, which is internal/poll.runtime_pollReset,
   311  // prepares a descriptor for polling in mode, which is 'r' or 'w'.
   312  // This returns an error code; the codes are defined above.
   313  //
   314  //go:linkname poll_runtime_pollReset internal/poll.runtime_pollReset
   315  func poll_runtime_pollReset(pd *pollDesc, mode int) int {
   316  	errcode := netpollcheckerr(pd, int32(mode))
   317  	if errcode != pollNoError {
   318  		return errcode
   319  	}
   320  	if mode == 'r' {
   321  		pd.rg.Store(pdNil)
   322  	} else if mode == 'w' {
   323  		pd.wg.Store(pdNil)
   324  	}
   325  	return pollNoError
   326  }
   327  
   328  // poll_runtime_pollWait, which is internal/poll.runtime_pollWait,
   329  // waits for a descriptor to be ready for reading or writing,
   330  // according to mode, which is 'r' or 'w'.
   331  // This returns an error code; the codes are defined above.
   332  //
   333  //go:linkname poll_runtime_pollWait internal/poll.runtime_pollWait
   334  func poll_runtime_pollWait(pd *pollDesc, mode int) int {
   335  	errcode := netpollcheckerr(pd, int32(mode))
   336  	if errcode != pollNoError {
   337  		return errcode
   338  	}
   339  	// As for now only Solaris, illumos, AIX and wasip1 use level-triggered IO.
   340  	if GOOS == "solaris" || GOOS == "illumos" || GOOS == "aix" || GOOS == "wasip1" {
   341  		netpollarm(pd, mode)
   342  	}
   343  	for !netpollblock(pd, int32(mode), false) {
   344  		errcode = netpollcheckerr(pd, int32(mode))
   345  		if errcode != pollNoError {
   346  			return errcode
   347  		}
   348  		// Can happen if timeout has fired and unblocked us,
   349  		// but before we had a chance to run, timeout has been reset.
   350  		// Pretend it has not happened and retry.
   351  	}
   352  	return pollNoError
   353  }
   354  
   355  //go:linkname poll_runtime_pollWaitCanceled internal/poll.runtime_pollWaitCanceled
   356  func poll_runtime_pollWaitCanceled(pd *pollDesc, mode int) {
   357  	// This function is used only on windows after a failed attempt to cancel
   358  	// a pending async IO operation. Wait for ioready, ignore closing or timeouts.
   359  	for !netpollblock(pd, int32(mode), true) {
   360  	}
   361  }
   362  
   363  //go:linkname poll_runtime_pollSetDeadline internal/poll.runtime_pollSetDeadline
   364  func poll_runtime_pollSetDeadline(pd *pollDesc, d int64, mode int) {
   365  	lock(&pd.lock)
   366  	if pd.closing {
   367  		unlock(&pd.lock)
   368  		return
   369  	}
   370  	rd0, wd0 := pd.rd, pd.wd
   371  	combo0 := rd0 > 0 && rd0 == wd0
   372  	if d > 0 {
   373  		d += nanotime()
   374  		if d <= 0 {
   375  			// If the user has a deadline in the future, but the delay calculation
   376  			// overflows, then set the deadline to the maximum possible value.
   377  			d = 1<<63 - 1
   378  		}
   379  	}
   380  	if mode == 'r' || mode == 'r'+'w' {
   381  		pd.rd = d
   382  	}
   383  	if mode == 'w' || mode == 'r'+'w' {
   384  		pd.wd = d
   385  	}
   386  	pd.publishInfo()
   387  	combo := pd.rd > 0 && pd.rd == pd.wd
   388  	rtf := netpollReadDeadline
   389  	if combo {
   390  		rtf = netpollDeadline
   391  	}
   392  	if pd.rt.f == nil {
   393  		if pd.rd > 0 {
   394  			pd.rt.f = rtf
   395  			// Copy current seq into the timer arg.
   396  			// Timer func will check the seq against current descriptor seq,
   397  			// if they differ the descriptor was reused or timers were reset.
   398  			pd.rt.arg = pd.makeArg()
   399  			pd.rt.seq = pd.rseq
   400  			resettimer(&pd.rt, pd.rd)
   401  		}
   402  	} else if pd.rd != rd0 || combo != combo0 {
   403  		pd.rseq++ // invalidate current timers
   404  		if pd.rd > 0 {
   405  			modtimer(&pd.rt, pd.rd, 0, rtf, pd.makeArg(), pd.rseq)
   406  		} else {
   407  			deltimer(&pd.rt)
   408  			pd.rt.f = nil
   409  		}
   410  	}
   411  	if pd.wt.f == nil {
   412  		if pd.wd > 0 && !combo {
   413  			pd.wt.f = netpollWriteDeadline
   414  			pd.wt.arg = pd.makeArg()
   415  			pd.wt.seq = pd.wseq
   416  			resettimer(&pd.wt, pd.wd)
   417  		}
   418  	} else if pd.wd != wd0 || combo != combo0 {
   419  		pd.wseq++ // invalidate current timers
   420  		if pd.wd > 0 && !combo {
   421  			modtimer(&pd.wt, pd.wd, 0, netpollWriteDeadline, pd.makeArg(), pd.wseq)
   422  		} else {
   423  			deltimer(&pd.wt)
   424  			pd.wt.f = nil
   425  		}
   426  	}
   427  	// If we set the new deadline in the past, unblock currently pending IO if any.
   428  	// Note that pd.publishInfo has already been called, above, immediately after modifying rd and wd.
   429  	var rg, wg *g
   430  	if pd.rd < 0 {
   431  		rg = netpollunblock(pd, 'r', false)
   432  	}
   433  	if pd.wd < 0 {
   434  		wg = netpollunblock(pd, 'w', false)
   435  	}
   436  	unlock(&pd.lock)
   437  	if rg != nil {
   438  		netpollgoready(rg, 3)
   439  	}
   440  	if wg != nil {
   441  		netpollgoready(wg, 3)
   442  	}
   443  }
   444  
   445  //go:linkname poll_runtime_pollUnblock internal/poll.runtime_pollUnblock
   446  func poll_runtime_pollUnblock(pd *pollDesc) {
   447  	lock(&pd.lock)
   448  	if pd.closing {
   449  		throw("runtime: unblock on closing polldesc")
   450  	}
   451  	pd.closing = true
   452  	pd.rseq++
   453  	pd.wseq++
   454  	var rg, wg *g
   455  	pd.publishInfo()
   456  	rg = netpollunblock(pd, 'r', false)
   457  	wg = netpollunblock(pd, 'w', false)
   458  	if pd.rt.f != nil {
   459  		deltimer(&pd.rt)
   460  		pd.rt.f = nil
   461  	}
   462  	if pd.wt.f != nil {
   463  		deltimer(&pd.wt)
   464  		pd.wt.f = nil
   465  	}
   466  	unlock(&pd.lock)
   467  	if rg != nil {
   468  		netpollgoready(rg, 3)
   469  	}
   470  	if wg != nil {
   471  		netpollgoready(wg, 3)
   472  	}
   473  }
   474  
   475  // netpollready is called by the platform-specific netpoll function.
   476  // It declares that the fd associated with pd is ready for I/O.
   477  // The toRun argument is used to build a list of goroutines to return
   478  // from netpoll. The mode argument is 'r', 'w', or 'r'+'w' to indicate
   479  // whether the fd is ready for reading or writing or both.
   480  //
   481  // This may run while the world is stopped, so write barriers are not allowed.
   482  //
   483  //go:nowritebarrier
   484  func netpollready(toRun *gList, pd *pollDesc, mode int32) {
   485  	var rg, wg *g
   486  	if mode == 'r' || mode == 'r'+'w' {
   487  		rg = netpollunblock(pd, 'r', true)
   488  	}
   489  	if mode == 'w' || mode == 'r'+'w' {
   490  		wg = netpollunblock(pd, 'w', true)
   491  	}
   492  	if rg != nil {
   493  		toRun.push(rg)
   494  	}
   495  	if wg != nil {
   496  		toRun.push(wg)
   497  	}
   498  }
   499  
   500  func netpollcheckerr(pd *pollDesc, mode int32) int {
   501  	info := pd.info()
   502  	if info.closing() {
   503  		return pollErrClosing
   504  	}
   505  	if (mode == 'r' && info.expiredReadDeadline()) || (mode == 'w' && info.expiredWriteDeadline()) {
   506  		return pollErrTimeout
   507  	}
   508  	// Report an event scanning error only on a read event.
   509  	// An error on a write event will be captured in a subsequent
   510  	// write call that is able to report a more specific error.
   511  	if mode == 'r' && info.eventErr() {
   512  		return pollErrNotPollable
   513  	}
   514  	return pollNoError
   515  }
   516  
   517  func netpollblockcommit(gp *g, gpp unsafe.Pointer) bool {
   518  	r := atomic.Casuintptr((*uintptr)(gpp), pdWait, uintptr(unsafe.Pointer(gp)))
   519  	if r {
   520  		// Bump the count of goroutines waiting for the poller.
   521  		// The scheduler uses this to decide whether to block
   522  		// waiting for the poller if there is nothing else to do.
   523  		netpollWaiters.Add(1)
   524  	}
   525  	return r
   526  }
   527  
   528  func netpollgoready(gp *g, traceskip int) {
   529  	netpollWaiters.Add(-1)
   530  	goready(gp, traceskip+1)
   531  }
   532  
   533  // returns true if IO is ready, or false if timed out or closed
   534  // waitio - wait only for completed IO, ignore errors
   535  // Concurrent calls to netpollblock in the same mode are forbidden, as pollDesc
   536  // can hold only a single waiting goroutine for each mode.
   537  func netpollblock(pd *pollDesc, mode int32, waitio bool) bool {
   538  	gpp := &pd.rg
   539  	if mode == 'w' {
   540  		gpp = &pd.wg
   541  	}
   542  
   543  	// set the gpp semaphore to pdWait
   544  	for {
   545  		// Consume notification if already ready.
   546  		if gpp.CompareAndSwap(pdReady, pdNil) {
   547  			return true
   548  		}
   549  		if gpp.CompareAndSwap(pdNil, pdWait) {
   550  			break
   551  		}
   552  
   553  		// Double check that this isn't corrupt; otherwise we'd loop
   554  		// forever.
   555  		if v := gpp.Load(); v != pdReady && v != pdNil {
   556  			throw("runtime: double wait")
   557  		}
   558  	}
   559  
   560  	// need to recheck error states after setting gpp to pdWait
   561  	// this is necessary because runtime_pollUnblock/runtime_pollSetDeadline/deadlineimpl
   562  	// do the opposite: store to closing/rd/wd, publishInfo, load of rg/wg
   563  	if waitio || netpollcheckerr(pd, mode) == pollNoError {
   564  		gopark(netpollblockcommit, unsafe.Pointer(gpp), waitReasonIOWait, traceBlockNet, 5)
   565  	}
   566  	// be careful to not lose concurrent pdReady notification
   567  	old := gpp.Swap(pdNil)
   568  	if old > pdWait {
   569  		throw("runtime: corrupted polldesc")
   570  	}
   571  	return old == pdReady
   572  }
   573  
   574  func netpollunblock(pd *pollDesc, mode int32, ioready bool) *g {
   575  	gpp := &pd.rg
   576  	if mode == 'w' {
   577  		gpp = &pd.wg
   578  	}
   579  
   580  	for {
   581  		old := gpp.Load()
   582  		if old == pdReady {
   583  			return nil
   584  		}
   585  		if old == pdNil && !ioready {
   586  			// Only set pdReady for ioready. runtime_pollWait
   587  			// will check for timeout/cancel before waiting.
   588  			return nil
   589  		}
   590  		var new uintptr
   591  		if ioready {
   592  			new = pdReady
   593  		}
   594  		if gpp.CompareAndSwap(old, new) {
   595  			if old == pdWait {
   596  				old = pdNil
   597  			}
   598  			return (*g)(unsafe.Pointer(old))
   599  		}
   600  	}
   601  }
   602  
   603  func netpolldeadlineimpl(pd *pollDesc, seq uintptr, read, write bool) {
   604  	lock(&pd.lock)
   605  	// Seq arg is seq when the timer was set.
   606  	// If it's stale, ignore the timer event.
   607  	currentSeq := pd.rseq
   608  	if !read {
   609  		currentSeq = pd.wseq
   610  	}
   611  	if seq != currentSeq {
   612  		// The descriptor was reused or timers were reset.
   613  		unlock(&pd.lock)
   614  		return
   615  	}
   616  	var rg *g
   617  	if read {
   618  		if pd.rd <= 0 || pd.rt.f == nil {
   619  			throw("runtime: inconsistent read deadline")
   620  		}
   621  		pd.rd = -1
   622  		pd.publishInfo()
   623  		rg = netpollunblock(pd, 'r', false)
   624  	}
   625  	var wg *g
   626  	if write {
   627  		if pd.wd <= 0 || pd.wt.f == nil && !read {
   628  			throw("runtime: inconsistent write deadline")
   629  		}
   630  		pd.wd = -1
   631  		pd.publishInfo()
   632  		wg = netpollunblock(pd, 'w', false)
   633  	}
   634  	unlock(&pd.lock)
   635  	if rg != nil {
   636  		netpollgoready(rg, 0)
   637  	}
   638  	if wg != nil {
   639  		netpollgoready(wg, 0)
   640  	}
   641  }
   642  
   643  func netpollDeadline(arg any, seq uintptr) {
   644  	netpolldeadlineimpl(arg.(*pollDesc), seq, true, true)
   645  }
   646  
   647  func netpollReadDeadline(arg any, seq uintptr) {
   648  	netpolldeadlineimpl(arg.(*pollDesc), seq, true, false)
   649  }
   650  
   651  func netpollWriteDeadline(arg any, seq uintptr) {
   652  	netpolldeadlineimpl(arg.(*pollDesc), seq, false, true)
   653  }
   654  
   655  func (c *pollCache) alloc() *pollDesc {
   656  	lock(&c.lock)
   657  	if c.first == nil {
   658  		const pdSize = unsafe.Sizeof(pollDesc{})
   659  		n := pollBlockSize / pdSize
   660  		if n == 0 {
   661  			n = 1
   662  		}
   663  		// Must be in non-GC memory because can be referenced
   664  		// only from epoll/kqueue internals.
   665  		mem := persistentalloc(n*pdSize, 0, &memstats.other_sys)
   666  		for i := uintptr(0); i < n; i++ {
   667  			pd := (*pollDesc)(add(mem, i*pdSize))
   668  			pd.link = c.first
   669  			c.first = pd
   670  		}
   671  	}
   672  	pd := c.first
   673  	c.first = pd.link
   674  	lockInit(&pd.lock, lockRankPollDesc)
   675  	unlock(&c.lock)
   676  	return pd
   677  }
   678  
   679  // makeArg converts pd to an interface{}.
   680  // makeArg does not do any allocation. Normally, such
   681  // a conversion requires an allocation because pointers to
   682  // types which embed runtime/internal/sys.NotInHeap (which pollDesc is)
   683  // must be stored in interfaces indirectly. See issue 42076.
   684  func (pd *pollDesc) makeArg() (i any) {
   685  	x := (*eface)(unsafe.Pointer(&i))
   686  	x._type = pdType
   687  	x.data = unsafe.Pointer(&pd.self)
   688  	return
   689  }
   690  
   691  var (
   692  	pdEface any    = (*pollDesc)(nil)
   693  	pdType  *_type = efaceOf(&pdEface)._type
   694  )
   695
View as plain text