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sync: release Pool memory during second and later GCs
Pool memory was only being released during the first GC after the first Put.

Put assumes that p.local != nil means p is on the allPools list.
poolCleanup (called during each GC) removed each pool from allPools
but did not clear p.local, so each pool was cleared by exactly one GC
and then never cleared again.

This bug was introduced late in the Go 1.3 release cycle.

Fixes #8979.

LGTM=rsc
R=golang-codereviews, bradfitz, r, rsc
CC=golang-codereviews, khr
https://golang.org/cl/162980043
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dvyukov committed Oct 22, 2014
1 parent 18051c0 commit af3868f1879c7f8bef1a4ac43cfe1ab1304ad6a4
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Showing 2 changed files with 35 additions and 21 deletions.
@@ -200,6 +200,8 @@ func poolCleanup() {
}
l.shared = nil
}
p.local = nil
p.localSize = 0
}
allPools = []*Pool{}
}
@@ -69,32 +69,44 @@ func TestPoolNew(t *testing.T) {
}
}

// Test that Pool does not hold pointers to previously cached
// resources
// Test that Pool does not hold pointers to previously cached resources.
func TestPoolGC(t *testing.T) {
testPool(t, true)
}

// Test that Pool releases resources on GC.
func TestPoolRelease(t *testing.T) {
testPool(t, false)
}

func testPool(t *testing.T, drain bool) {
var p Pool
var fin uint32
const N = 100
for i := 0; i < N; i++ {
v := new(string)
runtime.SetFinalizer(v, func(vv *string) {
atomic.AddUint32(&fin, 1)
})
p.Put(v)
}
for i := 0; i < N; i++ {
p.Get()
}
for i := 0; i < 5; i++ {
runtime.GC()
time.Sleep(time.Duration(i*100+10) * time.Millisecond)
// 1 pointer can remain on stack or elsewhere
if atomic.LoadUint32(&fin) >= N-1 {
return
loop:
for try := 0; try < 3; try++ {
var fin, fin1 uint32
for i := 0; i < N; i++ {
v := new(string)
runtime.SetFinalizer(v, func(vv *string) {
atomic.AddUint32(&fin, 1)
})
p.Put(v)
}
if drain {
for i := 0; i < N; i++ {
p.Get()
}
}
for i := 0; i < 5; i++ {
runtime.GC()
time.Sleep(time.Duration(i*100+10) * time.Millisecond)
// 1 pointer can remain on stack or elsewhere
if fin1 = atomic.LoadUint32(&fin); fin1 >= N-1 {
continue loop
}
}
t.Fatalf("only %v out of %v resources are finalized on try %v", fin1, N, try)
}
t.Fatalf("only %v out of %v resources are finalized",
atomic.LoadUint32(&fin), N)
}

func TestPoolStress(t *testing.T) {

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