diff options
author | Russ Cox <rsc@golang.org> | 2014-10-06 14:18:09 -0400 |
---|---|---|
committer | Russ Cox <rsc@golang.org> | 2014-10-06 14:18:09 -0400 |
commit | 7ad347e9e6e3bc5723b709768c87e87bd4c7493c (patch) | |
tree | e95fb9f2bfed86d8f08c21769cd8f02e51e40c89 /src | |
parent | 5869c235d76fb8341743989d86d8565ae8d211d3 (diff) | |
download | go-7ad347e9e6e3bc5723b709768c87e87bd4c7493c.tar.gz |
runtime: update docs, code for SetFinalizer
At last minute before 1.3 we relaxed SetFinalizer to avoid
crashes when you pass the result of a global alloc to it.
This avoids the crash but makes SetFinalizer a bit too relaxed.
Document that the finalizer of a global allocation may not run.
Tighten the SetFinalizer check to ignore a global allocation but
not ignore everything else.
Fixes issue 7656.
LGTM=r, iant
R=golang-codereviews, iant, r
CC=dvyukov, golang-codereviews, khr, rlh
https://codereview.appspot.com/145930043
Diffstat (limited to 'src')
-rw-r--r-- | src/runtime/malloc.go | 37 | ||||
-rw-r--r-- | src/runtime/mfinal_test.go | 13 |
2 files changed, 33 insertions, 17 deletions
diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go index fc22cc29e..99d14e314 100644 --- a/src/runtime/malloc.go +++ b/src/runtime/malloc.go @@ -488,6 +488,10 @@ func GC() { gogc(2) } +// linker-provided +var noptrdata struct{} +var enoptrbss struct{} + // SetFinalizer sets the finalizer associated with x to f. // When the garbage collector finds an unreachable block // with an associated finalizer, it clears the association and runs @@ -527,6 +531,10 @@ func GC() { // It is not guaranteed that a finalizer will run if the size of *x is // zero bytes. // +// It is not guaranteed that a finalizer will run for objects allocated +// in initializers for package-level variables. Such objects may be +// linker-allocated, not heap-allocated. +// // A single goroutine runs all finalizers for a program, sequentially. // If a finalizer must run for a long time, it should do so by starting // a new goroutine. @@ -544,24 +552,25 @@ func SetFinalizer(obj interface{}, finalizer interface{}) { gothrow("nil elem type!") } - // As an implementation detail we do not run finalizers for zero-sized objects, - // because we use &runtime·zerobase for all such allocations. - if ot.elem.size == 0 { - return - } - // find the containing object _, base, _ := findObject(e.data) - // The following check is required for cases when a user passes a pointer to composite - // literal, but compiler makes it a pointer to global. For example: - // var Foo = &Object{} - // func main() { - // runtime.SetFinalizer(Foo, nil) - // } - // See issue 7656. if base == nil { - return + // 0-length objects are okay. + if e.data == unsafe.Pointer(&zerobase) { + return + } + + // Global initializers might be linker-allocated. + // var Foo = &Object{} + // func main() { + // runtime.SetFinalizer(Foo, nil) + // } + // The segments are, in order: text, rodata, noptrdata, data, bss, noptrbss. + if uintptr(unsafe.Pointer(&noptrdata)) <= uintptr(e.data) && uintptr(e.data) < uintptr(unsafe.Pointer(&enoptrbss)) { + return + } + gothrow("runtime.SetFinalizer: pointer not in allocated block") } if e.data != base { diff --git a/src/runtime/mfinal_test.go b/src/runtime/mfinal_test.go index 6b53888ab..d2cead287 100644 --- a/src/runtime/mfinal_test.go +++ b/src/runtime/mfinal_test.go @@ -44,10 +44,17 @@ func TestFinalizerType(t *testing.T) { {func(x *int) interface{} { return (*Tint)(x) }, func(v Tinter) { finalize((*int)(v.(*Tint))) }}, } - for _, tt := range finalizerTests { + for i, tt := range finalizerTests { done := make(chan bool, 1) go func() { - v := new(int) + // allocate struct with pointer to avoid hitting tinyalloc. + // Otherwise we can't be sure when the allocation will + // be freed. + type T struct { + v int + p unsafe.Pointer + } + v := &new(T).v *v = 97531 runtime.SetFinalizer(tt.convert(v), tt.finalizer) v = nil @@ -58,7 +65,7 @@ func TestFinalizerType(t *testing.T) { select { case <-ch: case <-time.After(time.Second * 4): - t.Errorf("finalizer for type %T didn't run", tt.finalizer) + t.Errorf("#%d: finalizer for type %T didn't run", i, tt.finalizer) } } } |