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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build unix
package poll
import (
"io"
"runtime"
"syscall"
)
// Writev wraps the writev system call.
func (fd *FD) Writev(v *[][]byte) (int64, error) {
if err := fd.writeLock(); err != nil {
return 0, err
}
defer fd.writeUnlock()
if err := fd.pd.prepareWrite(fd.isFile); err != nil {
return 0, err
}
var iovecs []syscall.Iovec
if fd.iovecs != nil {
iovecs = *fd.iovecs
}
// TODO: read from sysconf(_SC_IOV_MAX)? The Linux default is
// 1024 and this seems conservative enough for now. Darwin's
// UIO_MAXIOV also seems to be 1024.
maxVec := 1024
if runtime.GOOS == "aix" || runtime.GOOS == "solaris" {
// IOV_MAX is set to XOPEN_IOV_MAX on AIX and Solaris.
maxVec = 16
}
var n int64
var err error
for len(*v) > 0 {
iovecs = iovecs[:0]
for _, chunk := range *v {
if len(chunk) == 0 {
continue
}
iovecs = append(iovecs, newIovecWithBase(&chunk[0]))
if fd.IsStream && len(chunk) > 1<<30 {
iovecs[len(iovecs)-1].SetLen(1 << 30)
break // continue chunk on next writev
}
iovecs[len(iovecs)-1].SetLen(len(chunk))
if len(iovecs) == maxVec {
break
}
}
if len(iovecs) == 0 {
break
}
if fd.iovecs == nil {
fd.iovecs = new([]syscall.Iovec)
}
*fd.iovecs = iovecs // cache
var wrote uintptr
wrote, err = writev(fd.Sysfd, iovecs)
if wrote == ^uintptr(0) {
wrote = 0
}
TestHookDidWritev(int(wrote))
n += int64(wrote)
consume(v, int64(wrote))
for i := range iovecs {
iovecs[i] = syscall.Iovec{}
}
if err != nil {
if err == syscall.EINTR {
continue
}
if err == syscall.EAGAIN {
if err = fd.pd.waitWrite(fd.isFile); err == nil {
continue
}
}
break
}
if n == 0 {
err = io.ErrUnexpectedEOF
break
}
}
return n, err
}
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