writev.go

     1  // Copyright 2016 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 darwin || dragonfly || freebsd || illumos || linux || netbsd || openbsd
     6  
     7  package poll
     8  
     9  import (
    10  	"io"
    11  	"syscall"
    12  )
    13  
    14  // Writev wraps the writev system call.
    15  func (fd *FD) Writev(v *[][]byte) (int64, error) {
    16  	if err := fd.writeLock(); err != nil {
    17  		return 0, err
    18  	}
    19  	defer fd.writeUnlock()
    20  	if err := fd.pd.prepareWrite(fd.isFile); err != nil {
    21  		return 0, err
    22  	}
    23  
    24  	var iovecs []syscall.Iovec
    25  	if fd.iovecs != nil {
    26  		iovecs = *fd.iovecs
    27  	}
    28  	// TODO: read from sysconf(_SC_IOV_MAX)? The Linux default is
    29  	// 1024 and this seems conservative enough for now. Darwin's
    30  	// UIO_MAXIOV also seems to be 1024.
    31  	maxVec := 1024
    32  
    33  	var n int64
    34  	var err error
    35  	for len(*v) > 0 {
    36  		iovecs = iovecs[:0]
    37  		for _, chunk := range *v {
    38  			if len(chunk) == 0 {
    39  				continue
    40  			}
    41  			iovecs = append(iovecs, newIovecWithBase(&chunk[0]))
    42  			if fd.IsStream && len(chunk) > 1<<30 {
    43  				iovecs[len(iovecs)-1].SetLen(1 << 30)
    44  				break // continue chunk on next writev
    45  			}
    46  			iovecs[len(iovecs)-1].SetLen(len(chunk))
    47  			if len(iovecs) == maxVec {
    48  				break
    49  			}
    50  		}
    51  		if len(iovecs) == 0 {
    52  			break
    53  		}
    54  		if fd.iovecs == nil {
    55  			fd.iovecs = new([]syscall.Iovec)
    56  		}
    57  		*fd.iovecs = iovecs // cache
    58  
    59  		var wrote uintptr
    60  		wrote, err = writev(fd.Sysfd, iovecs)
    61  		if wrote == ^uintptr(0) {
    62  			wrote = 0
    63  		}
    64  		TestHookDidWritev(int(wrote))
    65  		n += int64(wrote)
    66  		consume(v, int64(wrote))
    67  		for i := range iovecs {
    68  			iovecs[i] = syscall.Iovec{}
    69  		}
    70  		if err != nil {
    71  			if err == syscall.EINTR {
    72  				continue
    73  			}
    74  			if err == syscall.EAGAIN {
    75  				if err = fd.pd.waitWrite(fd.isFile); err == nil {
    76  					continue
    77  				}
    78  			}
    79  			break
    80  		}
    81  		if n == 0 {
    82  			err = io.ErrUnexpectedEOF
    83  			break
    84  		}
    85  	}
    86  	return n, err
    87  }
    88
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