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Diffstat (limited to 'pkg/refsvfs2/refs_template.go')
| -rw-r--r-- | pkg/refsvfs2/refs_template.go | 161 |
1 files changed, 0 insertions, 161 deletions
diff --git a/pkg/refsvfs2/refs_template.go b/pkg/refsvfs2/refs_template.go deleted file mode 100644 index 55b0a60a1..000000000 --- a/pkg/refsvfs2/refs_template.go +++ /dev/null @@ -1,161 +0,0 @@ -// Copyright 2020 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 refs_template defines a template that can be used by reference -// counted objects. The template comes with leak checking capabilities. -package refs_template - -import ( - "fmt" - "sync/atomic" - - "gvisor.dev/gvisor/pkg/refsvfs2" -) - -// enableLogging indicates whether reference-related events should be logged (with -// stack traces). This is false by default and should only be set to true for -// debugging purposes, as it can generate an extremely large amount of output -// and drastically degrade performance. -const enableLogging = false - -// T is the type of the reference counted object. It is only used to customize -// debug output when leak checking. -type T interface{} - -// obj is used to customize logging. Note that we use a pointer to T so that -// we do not copy the entire object when passed as a format parameter. -var obj *T - -// Refs implements refs.RefCounter. It keeps a reference count using atomic -// operations and calls the destructor when the count reaches zero. -// -// NOTE: Do not introduce additional fields to the Refs struct. It is used by -// many filesystem objects, and we want to keep it as small as possible (i.e., -// the same size as using an int64 directly) to avoid taking up extra cache -// space. In general, this template should not be extended at the cost of -// performance. If it does not offer enough flexibility for a particular object -// (example: b/187877947), we should implement the RefCounter/CheckedObject -// interfaces manually. -// -// +stateify savable -type Refs struct { - // refCount is composed of two fields: - // - // [32-bit speculative references]:[32-bit real references] - // - // Speculative references are used for TryIncRef, to avoid a CompareAndSwap - // loop. See IncRef, DecRef and TryIncRef for details of how these fields are - // used. - refCount int64 -} - -// InitRefs initializes r with one reference and, if enabled, activates leak -// checking. -func (r *Refs) InitRefs() { - atomic.StoreInt64(&r.refCount, 1) - refsvfs2.Register(r) -} - -// RefType implements refsvfs2.CheckedObject.RefType. -func (r *Refs) RefType() string { - return fmt.Sprintf("%T", obj)[1:] -} - -// LeakMessage implements refsvfs2.CheckedObject.LeakMessage. -func (r *Refs) LeakMessage() string { - return fmt.Sprintf("[%s %p] reference count of %d instead of 0", r.RefType(), r, r.ReadRefs()) -} - -// LogRefs implements refsvfs2.CheckedObject.LogRefs. -func (r *Refs) LogRefs() bool { - return enableLogging -} - -// ReadRefs returns the current number of references. The returned count is -// inherently racy and is unsafe to use without external synchronization. -func (r *Refs) ReadRefs() int64 { - return atomic.LoadInt64(&r.refCount) -} - -// IncRef implements refs.RefCounter.IncRef. -// -//go:nosplit -func (r *Refs) IncRef() { - v := atomic.AddInt64(&r.refCount, 1) - if enableLogging { - refsvfs2.LogIncRef(r, v) - } - if v <= 1 { - panic(fmt.Sprintf("Incrementing non-positive count %p on %s", r, r.RefType())) - } -} - -// TryIncRef implements refs.TryRefCounter.TryIncRef. -// -// To do this safely without a loop, a speculative reference is first acquired -// on the object. This allows multiple concurrent TryIncRef calls to distinguish -// other TryIncRef calls from genuine references held. -// -//go:nosplit -func (r *Refs) TryIncRef() bool { - const speculativeRef = 1 << 32 - if v := atomic.AddInt64(&r.refCount, speculativeRef); int32(v) == 0 { - // This object has already been freed. - atomic.AddInt64(&r.refCount, -speculativeRef) - return false - } - - // Turn into a real reference. - v := atomic.AddInt64(&r.refCount, -speculativeRef+1) - if enableLogging { - refsvfs2.LogTryIncRef(r, v) - } - return true -} - -// DecRef implements refs.RefCounter.DecRef. -// -// Note that speculative references are counted here. Since they were added -// prior to real references reaching zero, they will successfully convert to -// real references. In other words, we see speculative references only in the -// following case: -// -// A: TryIncRef [speculative increase => sees non-negative references] -// B: DecRef [real decrease] -// A: TryIncRef [transform speculative to real] -// -//go:nosplit -func (r *Refs) DecRef(destroy func()) { - v := atomic.AddInt64(&r.refCount, -1) - if enableLogging { - refsvfs2.LogDecRef(r, v) - } - switch { - case v < 0: - panic(fmt.Sprintf("Decrementing non-positive ref count %p, owned by %s", r, r.RefType())) - - case v == 0: - refsvfs2.Unregister(r) - // Call the destructor. - if destroy != nil { - destroy() - } - } -} - -func (r *Refs) afterLoad() { - if r.ReadRefs() > 0 { - refsvfs2.Register(r) - } -} |