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vfs: factor waiting code from read and writes into common function

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This commit is contained in:
Nick Craig-Wood 2020-05-18 16:52:56 +01:00
parent 3de9bd9d04
commit 0f9267d5fc
2 changed files with 39 additions and 56 deletions
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71
vfs/read.go
View file

@ -212,6 +212,43 @@ func (fh *ReadFileHandle) ReadAt(p []byte, off int64) (n int, err error) {
return fh.readAt(p, off)
}
// This waits for *poff to equal off or aborts after the timeout.
//
// Waits here potentially affect all seeks so need to keep them short
//
// Call with fh.mu Locked
func waitSequential(what string, remote string, cond *sync.Cond, maxWait time.Duration, poff *int64, off int64) {
var (
timeout = time.NewTimer(maxWait)
done = make(chan struct{})
abort = false
)
go func() {
select {
case <-timeout.C:
// take the lock to make sure that cond.Wait() is called before
// cond.Broadcast. NB cond.L == mu
cond.L.Lock()
// set abort flag and give all the waiting goroutines a kick on timeout
abort = true
fs.Debugf(remote, "aborting in-sequence %s wait, off=%d", what, off)
cond.Broadcast()
cond.L.Unlock()
case <-done:
}
}()
for *poff != off && !abort {
fs.Debugf(remote, "waiting for in-sequence %s to %d for %v", what, off, maxWait)
cond.Wait()
}
// tidy up end timer
close(done)
timeout.Stop()
if *poff != off {
fs.Debugf(remote, "failed to wait for in-sequence %s to %d", what, off)
}
}
// Implementation of ReadAt - call with lock held
func (fh *ReadFileHandle) readAt(p []byte, off int64) (n int, err error) {
// defer log.Trace(fh.remote, "p[%d], off=%d", len(p), off)("n=%d, err=%v", &n, &err)
@ -229,39 +266,7 @@ func (fh *ReadFileHandle) readAt(p []byte, off int64) (n int, err error) {
maxBuf = len(p)
}
if gap := off - fh.offset; gap > 0 && gap < int64(8*maxBuf) {
// Set a background timer so we don't wait for long
// Waits here potentially affect all seeks so need to keep them short
// The default time here was made by finding the
// smallest when mounting a local backend that didn't
// cause seeks.
maxWait := fh.file.VFS().Opt.ReadWait
timeout := time.NewTimer(maxWait)
done := make(chan struct{})
abort := false
go func() {
select {
case <-timeout.C:
// take the lock to make sure that fh.cond.Wait() is called before
// fh.cond.Broadcast. NB fh.cond.L == fh.mu
fh.mu.Lock()
// set abort flag and give all the waiting goroutines a kick on timeout
abort = true
fs.Debugf(fh.remote, "aborting in-sequence read wait, off=%d", off)
fh.cond.Broadcast()
fh.mu.Unlock()
case <-done:
}
}()
for fh.offset != off && !abort {
fs.Debugf(fh.remote, "waiting for in-sequence read to %d for %v", off, maxWait)
fh.cond.Wait()
}
// tidy up end timer
close(done)
timeout.Stop()
if fh.offset != off {
fs.Debugf(fh.remote, "failed to wait for in-sequence read to %d", off)
}
waitSequential("read", fh.remote, fh.cond, fh.file.VFS().Opt.ReadWait, &fh.offset, off)
}
doSeek := off != fh.offset
if doSeek && fh.noSeek {

24
vfs/write.go
View file

@ -5,7 +5,6 @@ import (
"io"
"os"
"sync"
"sync/atomic"
"time"
"github.com/rclone/rclone/fs"
@ -131,28 +130,7 @@ func (fh *WriteFileHandle) writeAt(p []byte, off int64) (n int, err error) {
return 0, ECLOSED
}
if fh.offset != off {
// Set a background timer so we don't wait forever
maxWait := fh.file.VFS().Opt.WriteWait
timeout := time.NewTimer(maxWait)
done := make(chan struct{})
abort := int32(0)
go func() {
select {
case <-timeout.C:
// set abort flag an give all the waiting goroutines a kick on timeout
atomic.StoreInt32(&abort, 1)
fh.cond.Broadcast()
case <-done:
}
}()
// Wait for an in-sequence write or abort
for fh.offset != off && atomic.LoadInt32(&abort) == 0 {
// fs.Debugf(fh.remote, "waiting for in-sequence write to %d", off)
fh.cond.Wait()
}
// tidy up end timer
close(done)
timeout.Stop()
waitSequential("write", fh.remote, fh.cond, fh.file.VFS().Opt.WriteWait, &fh.offset, off)
}
if fh.offset != off {
fs.Errorf(fh.remote, "WriteFileHandle.Write: can't seek in file without --vfs-cache-mode >= writes")