221 lines
6.2 KiB
Go
221 lines
6.2 KiB
Go
// Copyright 2018 Google Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package tty
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import (
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"bytes"
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"sync"
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"gvisor.googlesource.com/gvisor/pkg/abi/linux"
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"gvisor.googlesource.com/gvisor/pkg/sentry/arch"
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"gvisor.googlesource.com/gvisor/pkg/sentry/context"
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"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
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"gvisor.googlesource.com/gvisor/pkg/syserror"
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"gvisor.googlesource.com/gvisor/pkg/waiter"
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)
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// queue represents one of the input or output queues between a pty master and
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// slave. Bytes written to a queue are added to the read buffer until it is
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// full, at which point they are written to the wait buffer. Bytes are
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// processed (i.e. undergo termios transformations) as they are added to the
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// read buffer. The read buffer is readable when its length is nonzero and
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// readable is true.
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//
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// +stateify savable
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type queue struct {
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// mu protects everything in queue.
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mu sync.Mutex `state:"nosave"`
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waiter.Queue `state:"zerovalue"`
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// readBuf is buffer of data ready to be read when readable is true.
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// This data has been processed.
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readBuf bytes.Buffer `state:".([]byte)"`
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// waitBuf contains data that can't fit into readBuf. It is put here
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// until it can be loaded into the read buffer. waitBuf contains data
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// that hasn't been processed.
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waitBuf bytes.Buffer `state:".([]byte)"`
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// readable indicates whether the read buffer can be read from. In
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// canonical mode, there can be an unterminated line in the read buffer,
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// so readable must be checked.
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readable bool
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// transform is the the queue's function for transforming bytes
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// entering the queue. For example, transform might convert all '\r's
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// entering the queue to '\n's.
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transformer
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}
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// saveReadBuf is invoked by stateify.
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func (q *queue) saveReadBuf() []byte {
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return append([]byte(nil), q.readBuf.Bytes()...)
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}
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// loadReadBuf is invoked by stateify.
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func (q *queue) loadReadBuf(b []byte) {
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q.readBuf.Write(b)
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}
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// saveWaitBuf is invoked by stateify.
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func (q *queue) saveWaitBuf() []byte {
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return append([]byte(nil), q.waitBuf.Bytes()...)
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}
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// loadWaitBuf is invoked by stateify.
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func (q *queue) loadWaitBuf(b []byte) {
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q.waitBuf.Write(b)
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}
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// readReadiness returns whether q is ready to be read from.
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func (q *queue) readReadiness(t *linux.KernelTermios) waiter.EventMask {
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q.mu.Lock()
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defer q.mu.Unlock()
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if q.readBuf.Len() > 0 && q.readable {
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return waiter.EventIn
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}
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return waiter.EventMask(0)
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}
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// writeReadiness returns whether q is ready to be written to.
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func (q *queue) writeReadiness(t *linux.KernelTermios) waiter.EventMask {
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// Like Linux, we don't impose a maximum size on what can be enqueued.
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return waiter.EventOut
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}
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// readableSize writes the number of readable bytes to userspace.
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func (q *queue) readableSize(ctx context.Context, io usermem.IO, args arch.SyscallArguments) error {
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q.mu.Lock()
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defer q.mu.Unlock()
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var size int32
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if q.readable {
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size = int32(q.readBuf.Len())
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}
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_, err := usermem.CopyObjectOut(ctx, io, args[2].Pointer(), size, usermem.IOOpts{
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AddressSpaceActive: true,
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})
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return err
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}
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// read reads from q to userspace.
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//
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// Preconditions:
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// * l.termiosMu must be held for reading.
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func (q *queue) read(ctx context.Context, dst usermem.IOSequence, l *lineDiscipline) (int64, error) {
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q.mu.Lock()
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defer q.mu.Unlock()
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if !q.readable {
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return 0, syserror.ErrWouldBlock
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}
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// Read out from the read buffer.
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n := canonMaxBytes
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if n > int(dst.NumBytes()) {
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n = int(dst.NumBytes())
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}
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if n > q.readBuf.Len() {
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n = q.readBuf.Len()
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}
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n, err := dst.Writer(ctx).Write(q.readBuf.Bytes()[:n])
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if err != nil {
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return 0, err
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}
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// Discard bytes read out.
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q.readBuf.Next(n)
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// If we read everything, this queue is no longer readable.
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if q.readBuf.Len() == 0 {
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q.readable = false
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}
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// Move data from the queue's wait buffer to its read buffer.
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q.pushWaitBufLocked(l)
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// If state changed, notify any waiters. If nothing was available to
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// read, let the caller know we could block.
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if n > 0 {
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q.Notify(waiter.EventOut)
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} else {
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return 0, syserror.ErrWouldBlock
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}
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return int64(n), nil
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}
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// write writes to q from userspace.
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//
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// Preconditions:
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// * l.termiosMu must be held for reading.
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func (q *queue) write(ctx context.Context, src usermem.IOSequence, l *lineDiscipline) (int64, error) {
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// TODO: Use CopyInTo/safemem to avoid extra copying.
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// Copy in the bytes to write from user-space.
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b := make([]byte, src.NumBytes())
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n, err := src.CopyIn(ctx, b)
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if err != nil {
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return 0, err
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}
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b = b[:n]
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return q.writeBytes(b, l)
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}
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// writeBytes writes to q from b.
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//
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// Preconditions:
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// * l.termiosMu must be held for reading.
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func (q *queue) writeBytes(b []byte, l *lineDiscipline) (int64, error) {
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q.mu.Lock()
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defer q.mu.Unlock()
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// Write as much as possible to the read buffer.
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n := q.transform(l, q, b)
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// Write remaining data to the wait buffer.
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nWaiting, _ := q.waitBuf.Write(b[n:])
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// If state changed, notify any waiters. If we were unable to write
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// anything, let the caller know we could block.
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if n > 0 {
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q.Notify(waiter.EventIn)
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} else if nWaiting == 0 {
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return 0, syserror.ErrWouldBlock
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}
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return int64(n + nWaiting), nil
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}
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// pushWaitBuf fills the queue's read buffer with data from the wait buffer.
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//
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// Preconditions:
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// * l.termiosMu must be held for reading.
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func (q *queue) pushWaitBuf(l *lineDiscipline) {
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q.mu.Lock()
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defer q.mu.Unlock()
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q.pushWaitBufLocked(l)
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}
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// Preconditions:
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// * l.termiosMu must be held for reading.
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// * q.mu must be locked.
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func (q *queue) pushWaitBufLocked(l *lineDiscipline) {
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// Remove bytes from the wait buffer and move them to the read buffer.
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n := q.transform(l, q, q.waitBuf.Bytes())
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q.waitBuf.Next(n)
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// If state changed, notify any waiters.
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if n > 0 {
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q.Notify(waiter.EventIn)
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}
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}
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