diff options
Diffstat (limited to 'src/runtime/proc.go')
| -rw-r--r-- | src/runtime/proc.go | 28 |
1 files changed, 27 insertions, 1 deletions
diff --git a/src/runtime/proc.go b/src/runtime/proc.go index 2c0b3df167..1d00930ac5 100644 --- a/src/runtime/proc.go +++ b/src/runtime/proc.go @@ -1389,10 +1389,27 @@ func needm(x byte) { var earlycgocallback = []byte("fatal error: cgo callback before cgo call\n") -// newextram allocates an m and puts it on the extra list. +// newextram allocates m's and puts them on the extra list. // It is called with a working local m, so that it can do things // like call schedlock and allocate. func newextram() { + c := atomic.Xchg(&extraMWaiters, 0) + if c > 0 { + for i := uint32(0); i < c; i++ { + oneNewExtraM() + } + } else { + // Make sure there is at least one extra M. + mp := lockextra(true) + unlockextra(mp) + if mp == nil { + oneNewExtraM() + } + } +} + +// oneNewExtraM allocates an m and puts it on the extra list. +func oneNewExtraM() { // Create extra goroutine locked to extra m. // The goroutine is the context in which the cgo callback will run. // The sched.pc will never be returned to, but setting it to @@ -1485,6 +1502,7 @@ func getm() uintptr { } var extram uintptr +var extraMWaiters uint32 // lockextra locks the extra list and returns the list head. // The caller must unlock the list by storing a new list head @@ -1495,6 +1513,7 @@ var extram uintptr func lockextra(nilokay bool) *m { const locked = 1 + incr := false for { old := atomic.Loaduintptr(&extram) if old == locked { @@ -1503,6 +1522,13 @@ func lockextra(nilokay bool) *m { continue } if old == 0 && !nilokay { + if !incr { + // Add 1 to the number of threads + // waiting for an M. + // This is cleared by newextram. + atomic.Xadd(&extraMWaiters, 1) + incr = true + } usleep(1) continue } |