libgo/go/runtime/proflabel.go

   1 // Copyright 2017 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 package runtime
   6
   7 import "unsafe"
   8
   9 var labelSync uintptr
  10
  11 //go:linkname runtime_setProfLabel runtime_pprof.runtime_setProfLabel
  12 func runtime_setProfLabel(labels unsafe.Pointer) {
  13         // Introduce race edge for read-back via profile.
  14         // This would more properly use &getg().labels as the sync address,
  15         // but we do the read in a signal handler and can't call the race runtime then.
  16         //
  17         // This uses racereleasemerge rather than just racerelease so
  18         // the acquire in profBuf.read synchronizes with *all* prior
  19         // setProfLabel operations, not just the most recent one. This
  20         // is important because profBuf.read will observe different
  21         // labels set by different setProfLabel operations on
  22         // different goroutines, so it needs to synchronize with all
  23         // of them (this wouldn't be an issue if we could synchronize
  24         // on &getg().labels since we would synchronize with each
  25         // most-recent labels write separately.)
  26         //
  27         // racereleasemerge is like a full read-modify-write on
  28         // labelSync, rather than just a store-release, so it carries
  29         // a dependency on the previous racereleasemerge, which
  30         // ultimately carries forward to the acquire in profBuf.read.
  31         if raceenabled {
  32                 racereleasemerge(unsafe.Pointer(&labelSync))
  33         }
  34         getg().labels = labels
  35 }
  36
  37 //go:linkname runtime_getProfLabel runtime_pprof.runtime_getProfLabel
  38 func runtime_getProfLabel() unsafe.Pointer {
  39         return getg().labels
  40 }