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Merge release-20210208.0-89-gba4dfa717 (automated)

This commit is contained in:
gVisor bot 2021-02-24 20:05:55 +00:00
parent 0bca8624f6 ba4dfa7172
commit 0328d62d64
6 changed files with 160 additions and 143 deletions
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134
pkg/gate/gate.go
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@ -1,134 +0,0 @@
// Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package gate provides a usage Gate synchronization primitive.
package gate
import (
"sync/atomic"
)
const (
// gateClosed is the bit set in the gate's user count to indicate that
// it has been closed. It is the MSB of the 32-bit field; the other 31
// bits carry the actual count.
gateClosed = 0x80000000
)
// Gate is a synchronization primitive that allows concurrent goroutines to
// "enter" it as long as it hasn't been closed yet. Once it's been closed,
// goroutines cannot enter it anymore, but are allowed to leave, and the closer
// will be informed when all goroutines have left.
//
// Many goroutines are allowed to enter the gate concurrently, but only one is
// allowed to close it.
//
// This is similar to a r/w critical section, except that goroutines "entering"
// never block: they either enter immediately or fail to enter. The closer will
// block waiting for all goroutines currently inside the gate to leave.
//
// This function is implemented efficiently. On x86, only one interlocked
// operation is performed on enter, and one on leave.
//
// This is useful, for example, in cases when a goroutine is trying to clean up
// an object for which multiple goroutines have pointers. In such a case, users
// would be required to enter and leave the gates, and the cleaner would wait
// until all users are gone (and no new ones are allowed) before proceeding.
//
// Users:
//
// if !g.Enter() {
// // Gate is closed, we can't use the object.
// return
// }
//
// // Do something with object.
// [...]
//
// g.Leave()
//
// Closer:
//
// // Prevent new users from using the object, and wait for the existing
// // ones to complete.
// g.Close()
//
// // Clean up the object.
// [...]
//
type Gate struct {
userCount uint32
done chan struct{}
}
// Enter tries to enter the gate. It will succeed if it hasn't been closed yet,
// in which case the caller must eventually call Leave().
//
// This function is thread-safe.
func (g *Gate) Enter() bool {
if g == nil {
return false
}
for {
v := atomic.LoadUint32(&g.userCount)
if v&gateClosed != 0 {
return false
}
if atomic.CompareAndSwapUint32(&g.userCount, v, v+1) {
return true
}
}
}
// Leave leaves the gate. This must only be called after a successful call to
// Enter(). If the gate has been closed and this is the last one inside the
// gate, it will notify the closer that the gate is done.
//
// This function is thread-safe.
func (g *Gate) Leave() {
for {
v := atomic.LoadUint32(&g.userCount)
if v&^gateClosed == 0 {
panic("leaving a gate with zero usage count")
}
if atomic.CompareAndSwapUint32(&g.userCount, v, v-1) {
if v == gateClosed+1 {
close(g.done)
}
return
}
}
}
// Close closes the gate for entering, and waits until all goroutines [that are
// currently inside the gate] leave before returning.
//
// Only one goroutine can call this function.
func (g *Gate) Close() {
for {
v := atomic.LoadUint32(&g.userCount)
if v&^gateClosed != 0 && g.done == nil {
g.done = make(chan struct{})
}
if atomic.CompareAndSwapUint32(&g.userCount, v, v|gateClosed) {
if v&^gateClosed != 0 {
<-g.done
}
return
}
}
}

3
pkg/gate/gate_state_autogen.go
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@ -1,3 +0,0 @@
// automatically generated by stateify.
package gate

150
pkg/sync/gate_unsafe.go Normal file
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@ -0,0 +1,150 @@
// Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package sync
import (
"fmt"
"math"
"sync/atomic"
"unsafe"
"gvisor.dev/gvisor/pkg/gohacks"
)
// Gate is a synchronization primitive that allows concurrent goroutines to
// "enter" it as long as it hasn't been closed yet. Once it's been closed,
// goroutines cannot enter it anymore, but are allowed to leave, and the closer
// will be informed when all goroutines have left.
//
// Gate is similar to WaitGroup:
//
// - Gate.Enter() is analogous to WaitGroup.Add(1), but may be called even if
// the Gate counter is 0 and fails if Gate.Close() has been called.
//
// - Gate.Leave() is equivalent to WaitGroup.Done().
//
// - Gate.Close() is analogous to WaitGroup.Wait(), but also causes future
// calls to Gate.Enter() to fail and may only be called once, from a single
// goroutine.
//
// This is useful, for example, in cases when a goroutine is trying to clean up
// an object for which multiple goroutines have pointers. In such a case, users
// would be required to enter and leave the Gate, and the cleaner would wait
// until all users are gone (and no new ones are allowed) before proceeding.
//
// Users:
//
// if !g.Enter() {
// // Gate is closed, we can't use the object.
// return
// }
//
// // Do something with object.
// [...]
//
// g.Leave()
//
// Closer:
//
// // Prevent new users from using the object, and wait for the existing
// // ones to complete.
// g.Close()
//
// // Clean up the object.
// [...]
//
type Gate struct {
userCount int32
closingG uintptr
}
const preparingG = 1
// Enter tries to enter the gate. It will succeed if it hasn't been closed yet,
// in which case the caller must eventually call Leave().
//
// This function is thread-safe.
func (g *Gate) Enter() bool {
if atomic.AddInt32(&g.userCount, 1) > 0 {
return true
}
g.leaveAfterFailedEnter()
return false
}
// leaveAfterFailedEnter is identical to Leave, but is marked noinline to
// prevent it from being inlined into Enter, since as of this writing inlining
// Leave into Enter prevents Enter from being inlined into its callers.
//go:noinline
func (g *Gate) leaveAfterFailedEnter() {
if atomic.AddInt32(&g.userCount, -1) == math.MinInt32 {
g.leaveClosed()
}
}
// Leave leaves the gate. This must only be called after a successful call to
// Enter(). If the gate has been closed and this is the last one inside the
// gate, it will notify the closer that the gate is done.
//
// This function is thread-safe.
func (g *Gate) Leave() {
if atomic.AddInt32(&g.userCount, -1) == math.MinInt32 {
g.leaveClosed()
}
}
func (g *Gate) leaveClosed() {
if atomic.LoadUintptr(&g.closingG) == 0 {
return
}
if g := atomic.SwapUintptr(&g.closingG, 0); g > preparingG {
goready(g, 0)
}
}
// Close closes the gate, causing future calls to Enter to fail, and waits
// until all goroutines that are currently inside the gate leave before
// returning.
//
// Only one goroutine can call this function.
func (g *Gate) Close() {
if atomic.LoadInt32(&g.userCount) == math.MinInt32 {
// The gate is already closed, with no goroutines inside. For legacy
// reasons, we have to allow Close to be called again in this case.
return
}
if v := atomic.AddInt32(&g.userCount, math.MinInt32); v == math.MinInt32 {
// userCount was already 0.
return
} else if v >= 0 {
panic("concurrent Close of sync.Gate")
}
if g := atomic.SwapUintptr(&g.closingG, preparingG); g != 0 {
panic(fmt.Sprintf("invalid sync.Gate.closingG during Close: %#x", g))
}
if atomic.LoadInt32(&g.userCount) == math.MinInt32 {
// The last call to Leave arrived while we were setting up closingG.
return
}
// WaitReasonSemacquire/TraceEvGoBlockSync are consistent with WaitGroup.
gopark(gateCommit, gohacks.Noescape(unsafe.Pointer(&g.closingG)), WaitReasonSemacquire, TraceEvGoBlockSync, 0)
}
//go:norace
//go:nosplit
func gateCommit(g uintptr, closingG unsafe.Pointer) bool {
return RaceUncheckedAtomicCompareAndSwapUintptr((*uintptr)(closingG), preparingG, g)
}

6
pkg/sync/runtime_unsafe.go
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@ -56,12 +56,16 @@ func goready(gp uintptr, traceskip int)
// Values for the reason argument to gopark, from Go's src/runtime/runtime2.go.
const (
WaitReasonSelect uint8 = 9
WaitReasonSelect uint8 = 9
WaitReasonChanReceive uint8 = 14
WaitReasonSemacquire uint8 = 18
)
// Values for the traceEv argument to gopark, from Go's src/runtime/trace.go.
const (
TraceEvGoBlockRecv byte = 23
TraceEvGoBlockSelect byte = 24
TraceEvGoBlockSync byte = 25
)
// Rand32 returns a non-cryptographically-secure random uint32.

6
pkg/tcpip/link/waitable/waitable.go
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@ -22,7 +22,7 @@
package waitable
import (
"gvisor.dev/gvisor/pkg/gate"
"gvisor.dev/gvisor/pkg/sync"
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/header"
"gvisor.dev/gvisor/pkg/tcpip/stack"
@ -30,10 +30,10 @@ import (
// Endpoint is a waitable link-layer endpoint.
type Endpoint struct {
dispatchGate gate.Gate
dispatchGate sync.Gate
dispatcher stack.NetworkDispatcher
writeGate gate.Gate
writeGate sync.Gate
lower stack.LinkEndpoint
}

4
pkg/unet/unet.go
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@ -23,7 +23,7 @@ import (
"sync/atomic"
"syscall"
"gvisor.dev/gvisor/pkg/gate"
"gvisor.dev/gvisor/pkg/sync"
)
// backlog is used for the listen request.
@ -67,7 +67,7 @@ func eventFD() (int, error) {
// Socket is a connected unix domain socket.
type Socket struct {
// gate protects use of fd.
gate gate.Gate
gate sync.Gate
// fd is the bound socket.
//