diff options
Diffstat (limited to 'pkg/sentry/kernel/futex')
| -rw-r--r-- | pkg/sentry/kernel/futex/BUILD | 57 | ||||
| -rwxr-xr-x | pkg/sentry/kernel/futex/atomicptr_bucket_unsafe.go | 37 | ||||
| -rwxr-xr-x | pkg/sentry/kernel/futex/futex_state_autogen.go | 79 | ||||
| -rw-r--r-- | pkg/sentry/kernel/futex/futex_test.go | 530 | ||||
| -rwxr-xr-x | pkg/sentry/kernel/futex/waiter_list.go | 182 |
5 files changed, 298 insertions, 587 deletions
diff --git a/pkg/sentry/kernel/futex/BUILD b/pkg/sentry/kernel/futex/BUILD deleted file mode 100644 index c5021f2db..000000000 --- a/pkg/sentry/kernel/futex/BUILD +++ /dev/null @@ -1,57 +0,0 @@ -load("//tools:defs.bzl", "go_library", "go_test") -load("//tools/go_generics:defs.bzl", "go_template_instance") - -package(licenses = ["notice"]) - -go_template_instance( - name = "atomicptr_bucket", - out = "atomicptr_bucket_unsafe.go", - package = "futex", - suffix = "Bucket", - template = "//pkg/sync:generic_atomicptr", - types = { - "Value": "bucket", - }, -) - -go_template_instance( - name = "waiter_list", - out = "waiter_list.go", - package = "futex", - prefix = "waiter", - template = "//pkg/ilist:generic_list", - types = { - "Element": "*Waiter", - "Linker": "*Waiter", - }, -) - -go_library( - name = "futex", - srcs = [ - "atomicptr_bucket_unsafe.go", - "futex.go", - "waiter_list.go", - ], - visibility = ["//pkg/sentry:internal"], - deps = [ - "//pkg/abi/linux", - "//pkg/context", - "//pkg/log", - "//pkg/sentry/memmap", - "//pkg/sync", - "//pkg/syserror", - "//pkg/usermem", - ], -) - -go_test( - name = "futex_test", - size = "small", - srcs = ["futex_test.go"], - library = ":futex", - deps = [ - "//pkg/sync", - "//pkg/usermem", - ], -) diff --git a/pkg/sentry/kernel/futex/atomicptr_bucket_unsafe.go b/pkg/sentry/kernel/futex/atomicptr_bucket_unsafe.go new file mode 100755 index 000000000..d3fdf09b0 --- /dev/null +++ b/pkg/sentry/kernel/futex/atomicptr_bucket_unsafe.go @@ -0,0 +1,37 @@ +package futex + +import ( + "sync/atomic" + "unsafe" +) + +// An AtomicPtr is a pointer to a value of type Value that can be atomically +// loaded and stored. The zero value of an AtomicPtr represents nil. +// +// Note that copying AtomicPtr by value performs a non-atomic read of the +// stored pointer, which is unsafe if Store() can be called concurrently; in +// this case, do `dst.Store(src.Load())` instead. +// +// +stateify savable +type AtomicPtrBucket struct { + ptr unsafe.Pointer `state:".(*bucket)"` +} + +func (p *AtomicPtrBucket) savePtr() *bucket { + return p.Load() +} + +func (p *AtomicPtrBucket) loadPtr(v *bucket) { + p.Store(v) +} + +// Load returns the value set by the most recent Store. It returns nil if there +// has been no previous call to Store. +func (p *AtomicPtrBucket) Load() *bucket { + return (*bucket)(atomic.LoadPointer(&p.ptr)) +} + +// Store sets the value returned by Load to x. +func (p *AtomicPtrBucket) Store(x *bucket) { + atomic.StorePointer(&p.ptr, (unsafe.Pointer)(x)) +} diff --git a/pkg/sentry/kernel/futex/futex_state_autogen.go b/pkg/sentry/kernel/futex/futex_state_autogen.go new file mode 100755 index 000000000..d5ed3466f --- /dev/null +++ b/pkg/sentry/kernel/futex/futex_state_autogen.go @@ -0,0 +1,79 @@ +// automatically generated by stateify. + +package futex + +import ( + "gvisor.dev/gvisor/pkg/state" +) + +func (x *AtomicPtrBucket) beforeSave() {} +func (x *AtomicPtrBucket) save(m state.Map) { + x.beforeSave() + var ptr *bucket = x.savePtr() + m.SaveValue("ptr", ptr) +} + +func (x *AtomicPtrBucket) afterLoad() {} +func (x *AtomicPtrBucket) load(m state.Map) { + m.LoadValue("ptr", new(*bucket), func(y interface{}) { x.loadPtr(y.(*bucket)) }) +} + +func (x *bucket) beforeSave() {} +func (x *bucket) save(m state.Map) { + x.beforeSave() + if !state.IsZeroValue(x.waiters) { + m.Failf("waiters is %v, expected zero", x.waiters) + } +} + +func (x *bucket) afterLoad() {} +func (x *bucket) load(m state.Map) { +} + +func (x *Manager) beforeSave() {} +func (x *Manager) save(m state.Map) { + x.beforeSave() + if !state.IsZeroValue(x.privateBuckets) { + m.Failf("privateBuckets is %v, expected zero", x.privateBuckets) + } + m.Save("sharedBucket", &x.sharedBucket) +} + +func (x *Manager) afterLoad() {} +func (x *Manager) load(m state.Map) { + m.Load("sharedBucket", &x.sharedBucket) +} + +func (x *waiterList) beforeSave() {} +func (x *waiterList) save(m state.Map) { + x.beforeSave() + m.Save("head", &x.head) + m.Save("tail", &x.tail) +} + +func (x *waiterList) afterLoad() {} +func (x *waiterList) load(m state.Map) { + m.Load("head", &x.head) + m.Load("tail", &x.tail) +} + +func (x *waiterEntry) beforeSave() {} +func (x *waiterEntry) save(m state.Map) { + x.beforeSave() + m.Save("next", &x.next) + m.Save("prev", &x.prev) +} + +func (x *waiterEntry) afterLoad() {} +func (x *waiterEntry) load(m state.Map) { + m.Load("next", &x.next) + m.Load("prev", &x.prev) +} + +func init() { + state.Register("pkg/sentry/kernel/futex.AtomicPtrBucket", (*AtomicPtrBucket)(nil), state.Fns{Save: (*AtomicPtrBucket).save, Load: (*AtomicPtrBucket).load}) + state.Register("pkg/sentry/kernel/futex.bucket", (*bucket)(nil), state.Fns{Save: (*bucket).save, Load: (*bucket).load}) + state.Register("pkg/sentry/kernel/futex.Manager", (*Manager)(nil), state.Fns{Save: (*Manager).save, Load: (*Manager).load}) + state.Register("pkg/sentry/kernel/futex.waiterList", (*waiterList)(nil), state.Fns{Save: (*waiterList).save, Load: (*waiterList).load}) + state.Register("pkg/sentry/kernel/futex.waiterEntry", (*waiterEntry)(nil), state.Fns{Save: (*waiterEntry).save, Load: (*waiterEntry).load}) +} diff --git a/pkg/sentry/kernel/futex/futex_test.go b/pkg/sentry/kernel/futex/futex_test.go deleted file mode 100644 index 7c5c7665b..000000000 --- a/pkg/sentry/kernel/futex/futex_test.go +++ /dev/null @@ -1,530 +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 futex - -import ( - "math" - "runtime" - "sync/atomic" - "syscall" - "testing" - "unsafe" - - "gvisor.dev/gvisor/pkg/sync" - "gvisor.dev/gvisor/pkg/usermem" -) - -// testData implements the Target interface, and allows us to -// treat the address passed for futex operations as an index in -// a byte slice for testing simplicity. -type testData []byte - -const sizeofInt32 = 4 - -func newTestData(size uint) testData { - return make([]byte, size) -} - -func (t testData) SwapUint32(addr usermem.Addr, new uint32) (uint32, error) { - val := atomic.SwapUint32((*uint32)(unsafe.Pointer(&t[addr])), new) - return val, nil -} - -func (t testData) CompareAndSwapUint32(addr usermem.Addr, old, new uint32) (uint32, error) { - if atomic.CompareAndSwapUint32((*uint32)(unsafe.Pointer(&t[addr])), old, new) { - return old, nil - } - return atomic.LoadUint32((*uint32)(unsafe.Pointer(&t[addr]))), nil -} - -func (t testData) LoadUint32(addr usermem.Addr) (uint32, error) { - return atomic.LoadUint32((*uint32)(unsafe.Pointer(&t[addr]))), nil -} - -func (t testData) GetSharedKey(addr usermem.Addr) (Key, error) { - return Key{ - Kind: KindSharedMappable, - Offset: uint64(addr), - }, nil -} - -func futexKind(private bool) string { - if private { - return "private" - } - return "shared" -} - -func newPreparedTestWaiter(t *testing.T, m *Manager, ta Target, addr usermem.Addr, private bool, val uint32, bitmask uint32) *Waiter { - w := NewWaiter() - if err := m.WaitPrepare(w, ta, addr, private, val, bitmask); err != nil { - t.Fatalf("WaitPrepare failed: %v", err) - } - return w -} - -func TestFutexWake(t *testing.T) { - for _, private := range []bool{false, true} { - t.Run(futexKind(private), func(t *testing.T) { - m := NewManager() - d := newTestData(sizeofInt32) - - // Start waiting for wakeup. - w := newPreparedTestWaiter(t, m, d, 0, private, 0, ^uint32(0)) - defer m.WaitComplete(w) - - // Perform a wakeup. - if n, err := m.Wake(d, 0, private, ^uint32(0), 1); err != nil || n != 1 { - t.Errorf("Wake: got (%d, %v), wanted (1, nil)", n, err) - } - - // Expect the waiter to have been woken. - if !w.woken() { - t.Error("waiter not woken") - } - }) - } -} - -func TestFutexWakeBitmask(t *testing.T) { - for _, private := range []bool{false, true} { - t.Run(futexKind(private), func(t *testing.T) { - m := NewManager() - d := newTestData(sizeofInt32) - - // Start waiting for wakeup. - w := newPreparedTestWaiter(t, m, d, 0, private, 0, 0x0000ffff) - defer m.WaitComplete(w) - - // Perform a wakeup using the wrong bitmask. - if n, err := m.Wake(d, 0, private, 0xffff0000, 1); err != nil || n != 0 { - t.Errorf("Wake with non-matching bitmask: got (%d, %v), wanted (0, nil)", n, err) - } - - // Expect the waiter to still be waiting. - if w.woken() { - t.Error("waiter woken unexpectedly") - } - - // Perform a wakeup using the right bitmask. - if n, err := m.Wake(d, 0, private, 0x00000001, 1); err != nil || n != 1 { - t.Errorf("Wake with matching bitmask: got (%d, %v), wanted (1, nil)", n, err) - } - - // Expect that the waiter was woken. - if !w.woken() { - t.Error("waiter not woken") - } - }) - } -} - -func TestFutexWakeTwo(t *testing.T) { - for _, private := range []bool{false, true} { - t.Run(futexKind(private), func(t *testing.T) { - m := NewManager() - d := newTestData(sizeofInt32) - - // Start three waiters waiting for wakeup. - var ws [3]*Waiter - for i := range ws { - ws[i] = newPreparedTestWaiter(t, m, d, 0, private, 0, ^uint32(0)) - defer m.WaitComplete(ws[i]) - } - - // Perform two wakeups. - const wakeups = 2 - if n, err := m.Wake(d, 0, private, ^uint32(0), 2); err != nil || n != wakeups { - t.Errorf("Wake: got (%d, %v), wanted (%d, nil)", n, err, wakeups) - } - - // Expect that exactly two waiters were woken. - // We don't get guarantees about exactly which two, - // (although we expect them to be w1 and w2). - awake := 0 - for i := range ws { - if ws[i].woken() { - awake++ - } - } - if awake != wakeups { - t.Errorf("got %d woken waiters, wanted %d", awake, wakeups) - } - }) - } -} - -func TestFutexWakeUnrelated(t *testing.T) { - for _, private := range []bool{false, true} { - t.Run(futexKind(private), func(t *testing.T) { - m := NewManager() - d := newTestData(2 * sizeofInt32) - - // Start two waiters waiting for wakeup on different addresses. - w1 := newPreparedTestWaiter(t, m, d, 0*sizeofInt32, private, 0, ^uint32(0)) - defer m.WaitComplete(w1) - w2 := newPreparedTestWaiter(t, m, d, 1*sizeofInt32, private, 0, ^uint32(0)) - defer m.WaitComplete(w2) - - // Perform two wakeups on the second address. - if n, err := m.Wake(d, 1*sizeofInt32, private, ^uint32(0), 2); err != nil || n != 1 { - t.Errorf("Wake: got (%d, %v), wanted (1, nil)", n, err) - } - - // Expect that only the second waiter was woken. - if w1.woken() { - t.Error("w1 woken unexpectedly") - } - if !w2.woken() { - t.Error("w2 not woken") - } - }) - } -} - -func TestWakeOpEmpty(t *testing.T) { - for _, private := range []bool{false, true} { - t.Run(futexKind(private), func(t *testing.T) { - m := NewManager() - d := newTestData(2 * sizeofInt32) - - // Perform wakeups with no waiters. - if n, err := m.WakeOp(d, 0, sizeofInt32, private, 10, 10, 0); err != nil || n != 0 { - t.Fatalf("WakeOp: got (%d, %v), wanted (0, nil)", n, err) - } - }) - } -} - -func TestWakeOpFirstNonEmpty(t *testing.T) { - for _, private := range []bool{false, true} { - t.Run(futexKind(private), func(t *testing.T) { - m := NewManager() - d := newTestData(8) - - // Add two waiters on address 0. - w1 := newPreparedTestWaiter(t, m, d, 0, private, 0, ^uint32(0)) - defer m.WaitComplete(w1) - w2 := newPreparedTestWaiter(t, m, d, 0, private, 0, ^uint32(0)) - defer m.WaitComplete(w2) - - // Perform 10 wakeups on address 0. - if n, err := m.WakeOp(d, 0, sizeofInt32, private, 10, 0, 0); err != nil || n != 2 { - t.Errorf("WakeOp: got (%d, %v), wanted (2, nil)", n, err) - } - - // Expect that both waiters were woken. - if !w1.woken() { - t.Error("w1 not woken") - } - if !w2.woken() { - t.Error("w2 not woken") - } - }) - } -} - -func TestWakeOpSecondNonEmpty(t *testing.T) { - for _, private := range []bool{false, true} { - t.Run(futexKind(private), func(t *testing.T) { - m := NewManager() - d := newTestData(8) - - // Add two waiters on address sizeofInt32. - w1 := newPreparedTestWaiter(t, m, d, sizeofInt32, private, 0, ^uint32(0)) - defer m.WaitComplete(w1) - w2 := newPreparedTestWaiter(t, m, d, sizeofInt32, private, 0, ^uint32(0)) - defer m.WaitComplete(w2) - - // Perform 10 wakeups on address sizeofInt32 (contingent on - // d.Op(0), which should succeed). - if n, err := m.WakeOp(d, 0, sizeofInt32, private, 0, 10, 0); err != nil || n != 2 { - t.Errorf("WakeOp: got (%d, %v), wanted (2, nil)", n, err) - } - - // Expect that both waiters were woken. - if !w1.woken() { - t.Error("w1 not woken") - } - if !w2.woken() { - t.Error("w2 not woken") - } - }) - } -} - -func TestWakeOpSecondNonEmptyFailingOp(t *testing.T) { - for _, private := range []bool{false, true} { - t.Run(futexKind(private), func(t *testing.T) { - m := NewManager() - d := newTestData(8) - - // Add two waiters on address sizeofInt32. - w1 := newPreparedTestWaiter(t, m, d, sizeofInt32, private, 0, ^uint32(0)) - defer m.WaitComplete(w1) - w2 := newPreparedTestWaiter(t, m, d, sizeofInt32, private, 0, ^uint32(0)) - defer m.WaitComplete(w2) - - // Perform 10 wakeups on address sizeofInt32 (contingent on - // d.Op(1), which should fail). - if n, err := m.WakeOp(d, 0, sizeofInt32, private, 0, 10, 1); err != nil || n != 0 { - t.Errorf("WakeOp: got (%d, %v), wanted (0, nil)", n, err) - } - - // Expect that neither waiter was woken. - if w1.woken() { - t.Error("w1 woken unexpectedly") - } - if w2.woken() { - t.Error("w2 woken unexpectedly") - } - }) - } -} - -func TestWakeOpAllNonEmpty(t *testing.T) { - for _, private := range []bool{false, true} { - t.Run(futexKind(private), func(t *testing.T) { - m := NewManager() - d := newTestData(8) - - // Add two waiters on address 0. - w1 := newPreparedTestWaiter(t, m, d, 0, private, 0, ^uint32(0)) - defer m.WaitComplete(w1) - w2 := newPreparedTestWaiter(t, m, d, 0, private, 0, ^uint32(0)) - defer m.WaitComplete(w2) - - // Add two waiters on address sizeofInt32. - w3 := newPreparedTestWaiter(t, m, d, sizeofInt32, private, 0, ^uint32(0)) - defer m.WaitComplete(w3) - w4 := newPreparedTestWaiter(t, m, d, sizeofInt32, private, 0, ^uint32(0)) - defer m.WaitComplete(w4) - - // Perform 10 wakeups on address 0 (unconditionally), and 10 - // wakeups on address sizeofInt32 (contingent on d.Op(0), which - // should succeed). - if n, err := m.WakeOp(d, 0, sizeofInt32, private, 10, 10, 0); err != nil || n != 4 { - t.Errorf("WakeOp: got (%d, %v), wanted (4, nil)", n, err) - } - - // Expect that all waiters were woken. - if !w1.woken() { - t.Error("w1 not woken") - } - if !w2.woken() { - t.Error("w2 not woken") - } - if !w3.woken() { - t.Error("w3 not woken") - } - if !w4.woken() { - t.Error("w4 not woken") - } - }) - } -} - -func TestWakeOpAllNonEmptyFailingOp(t *testing.T) { - for _, private := range []bool{false, true} { - t.Run(futexKind(private), func(t *testing.T) { - m := NewManager() - d := newTestData(8) - - // Add two waiters on address 0. - w1 := newPreparedTestWaiter(t, m, d, 0, private, 0, ^uint32(0)) - defer m.WaitComplete(w1) - w2 := newPreparedTestWaiter(t, m, d, 0, private, 0, ^uint32(0)) - defer m.WaitComplete(w2) - - // Add two waiters on address sizeofInt32. - w3 := newPreparedTestWaiter(t, m, d, sizeofInt32, private, 0, ^uint32(0)) - defer m.WaitComplete(w3) - w4 := newPreparedTestWaiter(t, m, d, sizeofInt32, private, 0, ^uint32(0)) - defer m.WaitComplete(w4) - - // Perform 10 wakeups on address 0 (unconditionally), and 10 - // wakeups on address sizeofInt32 (contingent on d.Op(1), which - // should fail). - if n, err := m.WakeOp(d, 0, sizeofInt32, private, 10, 10, 1); err != nil || n != 2 { - t.Errorf("WakeOp: got (%d, %v), wanted (2, nil)", n, err) - } - - // Expect that only the first two waiters were woken. - if !w1.woken() { - t.Error("w1 not woken") - } - if !w2.woken() { - t.Error("w2 not woken") - } - if w3.woken() { - t.Error("w3 woken unexpectedly") - } - if w4.woken() { - t.Error("w4 woken unexpectedly") - } - }) - } -} - -func TestWakeOpSameAddress(t *testing.T) { - for _, private := range []bool{false, true} { - t.Run(futexKind(private), func(t *testing.T) { - m := NewManager() - d := newTestData(8) - - // Add four waiters on address 0. - var ws [4]*Waiter - for i := range ws { - ws[i] = newPreparedTestWaiter(t, m, d, 0, private, 0, ^uint32(0)) - defer m.WaitComplete(ws[i]) - } - - // Perform 1 wakeup on address 0 (unconditionally), and 1 wakeup - // on address 0 (contingent on d.Op(0), which should succeed). - const wakeups = 2 - if n, err := m.WakeOp(d, 0, 0, private, 1, 1, 0); err != nil || n != wakeups { - t.Errorf("WakeOp: got (%d, %v), wanted (%d, nil)", n, err, wakeups) - } - - // Expect that exactly two waiters were woken. - awake := 0 - for i := range ws { - if ws[i].woken() { - awake++ - } - } - if awake != wakeups { - t.Errorf("got %d woken waiters, wanted %d", awake, wakeups) - } - }) - } -} - -func TestWakeOpSameAddressFailingOp(t *testing.T) { - for _, private := range []bool{false, true} { - t.Run(futexKind(private), func(t *testing.T) { - m := NewManager() - d := newTestData(8) - - // Add four waiters on address 0. - var ws [4]*Waiter - for i := range ws { - ws[i] = newPreparedTestWaiter(t, m, d, 0, private, 0, ^uint32(0)) - defer m.WaitComplete(ws[i]) - } - - // Perform 1 wakeup on address 0 (unconditionally), and 1 wakeup - // on address 0 (contingent on d.Op(1), which should fail). - const wakeups = 1 - if n, err := m.WakeOp(d, 0, 0, private, 1, 1, 1); err != nil || n != wakeups { - t.Errorf("WakeOp: got (%d, %v), wanted (%d, nil)", n, err, wakeups) - } - - // Expect that exactly one waiter was woken. - awake := 0 - for i := range ws { - if ws[i].woken() { - awake++ - } - } - if awake != wakeups { - t.Errorf("got %d woken waiters, wanted %d", awake, wakeups) - } - }) - } -} - -const ( - testMutexSize = sizeofInt32 - testMutexLocked uint32 = 1 - testMutexUnlocked uint32 = 0 -) - -// testMutex ties together a testData slice, an address, and a -// futex manager in order to implement the sync.Locker interface. -// Beyond being used as a Locker, this is a simple mechanism for -// changing the underlying values for simpler tests. -type testMutex struct { - a usermem.Addr - d testData - m *Manager -} - -func newTestMutex(addr usermem.Addr, d testData, m *Manager) *testMutex { - return &testMutex{a: addr, d: d, m: m} -} - -// Lock acquires the testMutex. -// This may wait for it to be available via the futex manager. -func (t *testMutex) Lock() { - for { - // Attempt to grab the lock. - if atomic.CompareAndSwapUint32( - (*uint32)(unsafe.Pointer(&t.d[t.a])), - testMutexUnlocked, - testMutexLocked) { - // Lock held. - return - } - - // Wait for it to be "not locked". - w := NewWaiter() - err := t.m.WaitPrepare(w, t.d, t.a, true, testMutexLocked, ^uint32(0)) - if err == syscall.EAGAIN { - continue - } - if err != nil { - // Should never happen. - panic("WaitPrepare returned unexpected error: " + err.Error()) - } - <-w.C - t.m.WaitComplete(w) - } -} - -// Unlock releases the testMutex. -// This will notify any waiters via the futex manager. -func (t *testMutex) Unlock() { - // Unlock. - atomic.StoreUint32((*uint32)(unsafe.Pointer(&t.d[t.a])), testMutexUnlocked) - - // Notify all waiters. - t.m.Wake(t.d, t.a, true, ^uint32(0), math.MaxInt32) -} - -// This function was shamelessly stolen from mutex_test.go. -func HammerMutex(l sync.Locker, loops int, cdone chan bool) { - for i := 0; i < loops; i++ { - l.Lock() - runtime.Gosched() - l.Unlock() - } - cdone <- true -} - -func TestMutexStress(t *testing.T) { - m := NewManager() - d := newTestData(testMutexSize) - tm := newTestMutex(0*testMutexSize, d, m) - c := make(chan bool) - - for i := 0; i < 10; i++ { - go HammerMutex(tm, 1000, c) - } - - for i := 0; i < 10; i++ { - <-c - } -} diff --git a/pkg/sentry/kernel/futex/waiter_list.go b/pkg/sentry/kernel/futex/waiter_list.go new file mode 100755 index 000000000..b6baa1b5b --- /dev/null +++ b/pkg/sentry/kernel/futex/waiter_list.go @@ -0,0 +1,182 @@ +package futex + +// ElementMapper provides an identity mapping by default. +// +// This can be replaced to provide a struct that maps elements to linker +// objects, if they are not the same. An ElementMapper is not typically +// required if: Linker is left as is, Element is left as is, or Linker and +// Element are the same type. +type waiterElementMapper struct{} + +// linkerFor maps an Element to a Linker. +// +// This default implementation should be inlined. +// +//go:nosplit +func (waiterElementMapper) linkerFor(elem *Waiter) *Waiter { return elem } + +// List is an intrusive list. Entries can be added to or removed from the list +// in O(1) time and with no additional memory allocations. +// +// The zero value for List is an empty list ready to use. +// +// To iterate over a list (where l is a List): +// for e := l.Front(); e != nil; e = e.Next() { +// // do something with e. +// } +// +// +stateify savable +type waiterList struct { + head *Waiter + tail *Waiter +} + +// Reset resets list l to the empty state. +func (l *waiterList) Reset() { + l.head = nil + l.tail = nil +} + +// Empty returns true iff the list is empty. +func (l *waiterList) Empty() bool { + return l.head == nil +} + +// Front returns the first element of list l or nil. +func (l *waiterList) Front() *Waiter { + return l.head +} + +// Back returns the last element of list l or nil. +func (l *waiterList) Back() *Waiter { + return l.tail +} + +// PushFront inserts the element e at the front of list l. +func (l *waiterList) PushFront(e *Waiter) { + linker := waiterElementMapper{}.linkerFor(e) + linker.SetNext(l.head) + linker.SetPrev(nil) + + if l.head != nil { + waiterElementMapper{}.linkerFor(l.head).SetPrev(e) + } else { + l.tail = e + } + + l.head = e +} + +// PushBack inserts the element e at the back of list l. +func (l *waiterList) PushBack(e *Waiter) { + linker := waiterElementMapper{}.linkerFor(e) + linker.SetNext(nil) + linker.SetPrev(l.tail) + + if l.tail != nil { + waiterElementMapper{}.linkerFor(l.tail).SetNext(e) + } else { + l.head = e + } + + l.tail = e +} + +// PushBackList inserts list m at the end of list l, emptying m. +func (l *waiterList) PushBackList(m *waiterList) { + if l.head == nil { + l.head = m.head + l.tail = m.tail + } else if m.head != nil { + waiterElementMapper{}.linkerFor(l.tail).SetNext(m.head) + waiterElementMapper{}.linkerFor(m.head).SetPrev(l.tail) + + l.tail = m.tail + } + + m.head = nil + m.tail = nil +} + +// InsertAfter inserts e after b. +func (l *waiterList) InsertAfter(b, e *Waiter) { + bLinker := waiterElementMapper{}.linkerFor(b) + eLinker := waiterElementMapper{}.linkerFor(e) + + a := bLinker.Next() + + eLinker.SetNext(a) + eLinker.SetPrev(b) + bLinker.SetNext(e) + + if a != nil { + waiterElementMapper{}.linkerFor(a).SetPrev(e) + } else { + l.tail = e + } +} + +// InsertBefore inserts e before a. +func (l *waiterList) InsertBefore(a, e *Waiter) { + aLinker := waiterElementMapper{}.linkerFor(a) + eLinker := waiterElementMapper{}.linkerFor(e) + + b := aLinker.Prev() + eLinker.SetNext(a) + eLinker.SetPrev(b) + aLinker.SetPrev(e) + + if b != nil { + waiterElementMapper{}.linkerFor(b).SetNext(e) + } else { + l.head = e + } +} + +// Remove removes e from l. +func (l *waiterList) Remove(e *Waiter) { + prev := waiterElementMapper{}.linkerFor(e).Prev() + next := waiterElementMapper{}.linkerFor(e).Next() + + if prev != nil { + waiterElementMapper{}.linkerFor(prev).SetNext(next) + } else { + l.head = next + } + + if next != nil { + waiterElementMapper{}.linkerFor(next).SetPrev(prev) + } else { + l.tail = prev + } +} + +// Entry is a default implementation of Linker. Users can add anonymous fields +// of this type to their structs to make them automatically implement the +// methods needed by List. +// +// +stateify savable +type waiterEntry struct { + next *Waiter + prev *Waiter +} + +// Next returns the entry that follows e in the list. +func (e *waiterEntry) Next() *Waiter { + return e.next +} + +// Prev returns the entry that precedes e in the list. +func (e *waiterEntry) Prev() *Waiter { + return e.prev +} + +// SetNext assigns 'entry' as the entry that follows e in the list. +func (e *waiterEntry) SetNext(elem *Waiter) { + e.next = elem +} + +// SetPrev assigns 'entry' as the entry that precedes e in the list. +func (e *waiterEntry) SetPrev(elem *Waiter) { + e.prev = elem +} |