diff options
Diffstat (limited to 'libgo/go/runtime/select.go')
| -rw-r--r-- | libgo/go/runtime/select.go | 76 |
1 files changed, 9 insertions, 67 deletions
diff --git a/libgo/go/runtime/select.go b/libgo/go/runtime/select.go index 9f8ac49..096af52 100644 --- a/libgo/go/runtime/select.go +++ b/libgo/go/runtime/select.go @@ -88,7 +88,7 @@ func newselect(sel *hselect, selsize int64, size int32) { } func selectsend(sel *hselect, c *hchan, elem unsafe.Pointer) { - pc := getcallerpc(unsafe.Pointer(&sel)) + pc := getcallerpc() i := sel.ncase if i >= sel.tcase { throw("selectsend: too many cases") @@ -109,7 +109,7 @@ func selectsend(sel *hselect, c *hchan, elem unsafe.Pointer) { } func selectrecv(sel *hselect, c *hchan, elem unsafe.Pointer, received *bool) { - pc := getcallerpc(unsafe.Pointer(&sel)) + pc := getcallerpc() i := sel.ncase if i >= sel.tcase { throw("selectrecv: too many cases") @@ -131,7 +131,7 @@ func selectrecv(sel *hselect, c *hchan, elem unsafe.Pointer, received *bool) { } func selectdefault(sel *hselect) { - pc := getcallerpc(unsafe.Pointer(&sel)) + pc := getcallerpc() i := sel.ncase if i >= sel.tcase { throw("selectdefault: too many cases") @@ -301,7 +301,6 @@ func selectgo(sel *hselect) int { var ( gp *g - done uint32 sg *sudog c *hchan k *scase @@ -368,7 +367,6 @@ loop: // pass 2 - enqueue on all chans gp = getg() - done = 0 if gp.waiting != nil { throw("gp.waiting != nil") } @@ -382,8 +380,7 @@ loop: c = cas.c sg := acquireSudog() sg.g = gp - // Note: selectdone is adjusted for stack copies in stack1.go:adjustsudogs - sg.selectdone = (*uint32)(noescape(unsafe.Pointer(&done))) + sg.isSelect = true // No stack splits between assigning elem and enqueuing // sg on gp.waiting where copystack can find it. sg.elem = cas.elem @@ -409,62 +406,9 @@ loop: gp.param = nil gopark(selparkcommit, nil, "select", traceEvGoBlockSelect, 1) - // While we were asleep, some goroutine came along and completed - // one of the cases in the select and woke us up (called ready). - // As part of that process, the goroutine did a cas on done above - // (aka *sg.selectdone for all queued sg) to win the right to - // complete the select. Now done = 1. - // - // If we copy (grow) our own stack, we will update the - // selectdone pointers inside the gp.waiting sudog list to point - // at the new stack. Another goroutine attempting to - // complete one of our (still linked in) select cases might - // see the new selectdone pointer (pointing at the new stack) - // before the new stack has real data; if the new stack has done = 0 - // (before the old values are copied over), the goroutine might - // do a cas via sg.selectdone and incorrectly believe that it has - // won the right to complete the select, executing a second - // communication and attempting to wake us (call ready) again. - // - // Then things break. - // - // The best break is that the goroutine doing ready sees the - // _Gcopystack status and throws, as in #17007. - // A worse break would be for us to continue on, start running real code, - // block in a semaphore acquisition (sema.go), and have the other - // goroutine wake us up without having really acquired the semaphore. - // That would result in the goroutine spuriously running and then - // queue up another spurious wakeup when the semaphore really is ready. - // In general the situation can cascade until something notices the - // problem and causes a crash. - // - // A stack shrink does not have this problem, because it locks - // all the channels that are involved first, blocking out the - // possibility of a cas on selectdone. - // - // A stack growth before gopark above does not have this - // problem, because we hold those channel locks (released by - // selparkcommit). - // - // A stack growth after sellock below does not have this - // problem, because again we hold those channel locks. - // - // The only problem is a stack growth during sellock. - // To keep that from happening, run sellock on the system stack. - // - // It might be that we could avoid this if copystack copied the - // stack before calling adjustsudogs. In that case, - // syncadjustsudogs would need to recopy the tiny part that - // it copies today, resulting in a little bit of extra copying. - // - // An even better fix, not for the week before a release candidate, - // would be to put space in every sudog and make selectdone - // point at (say) the space in the first sudog. - - systemstack(func() { - sellock(scases, lockorder) - }) + sellock(scases, lockorder) + gp.selectDone = 0 sg = (*sudog)(gp.param) gp.param = nil @@ -477,7 +421,7 @@ loop: sglist = gp.waiting // Clear all elem before unlinking from gp.waiting. for sg1 := gp.waiting; sg1 != nil; sg1 = sg1.waitlink { - sg1.selectdone = nil + sg1.isSelect = false sg1.elem = nil sg1.c = nil } @@ -528,10 +472,8 @@ loop: print("wait-return: sel=", sel, " c=", c, " cas=", cas, " kind=", cas.kind, "\n") } - if cas.kind == caseRecv { - if cas.receivedp != nil { - *cas.receivedp = true - } + if cas.kind == caseRecv && cas.receivedp != nil { + *cas.receivedp = true } if raceenabled { |