runtime: replace raw traceEv with traceBlockReason in gopark

This change adds traceBlockReason which leaks fewer implementation
details of the tracer to the runtime. Currently, gopark is called with
an explicit trace event, but this leaks details about trace internals
throughout the runtime.

This change will make it easier to change out the trace implementation.

Change-Id: Id633e1704d2c8838c6abd1214d9695537c4ac7db
Reviewed-on: https://go-review.googlesource.com/c/go/+/494185
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>

src/runtime/chan.go

@@ -162,7 +162,7 @@ func chansend(c *hchan, ep unsafe.Pointer, block bool, callerpc uintptr) bool {
 		if !block {
 			return false
 		}
-		gopark(nil, nil, waitReasonChanSendNilChan, traceEvGoStop, 2)
+		gopark(nil, nil, waitReasonChanSendNilChan, traceBlockForever, 2)
 		throw("unreachable")
 	}
 
@@ -256,7 +256,7 @@ func chansend(c *hchan, ep unsafe.Pointer, block bool, callerpc uintptr) bool {
 	// changes and when we set gp.activeStackChans is not safe for
 	// stack shrinking.
 	gp.parkingOnChan.Store(true)
-	gopark(chanparkcommit, unsafe.Pointer(&c.lock), waitReasonChanSend, traceEvGoBlockSend, 2)
+	gopark(chanparkcommit, unsafe.Pointer(&c.lock), waitReasonChanSend, traceBlockChanSend, 2)
 	// Ensure the value being sent is kept alive until the
 	// receiver copies it out. The sudog has a pointer to the
 	// stack object, but sudogs aren't considered as roots of the
@@ -466,7 +466,7 @@ func chanrecv(c *hchan, ep unsafe.Pointer, block bool) (selected, received bool)
 		if !block {
 			return
 		}
-		gopark(nil, nil, waitReasonChanReceiveNilChan, traceEvGoStop, 2)
+		gopark(nil, nil, waitReasonChanReceiveNilChan, traceBlockForever, 2)
 		throw("unreachable")
 	}
 
@@ -580,7 +580,7 @@ func chanrecv(c *hchan, ep unsafe.Pointer, block bool) (selected, received bool)
 	// changes and when we set gp.activeStackChans is not safe for
 	// stack shrinking.
 	gp.parkingOnChan.Store(true)
-	gopark(chanparkcommit, unsafe.Pointer(&c.lock), waitReasonChanReceive, traceEvGoBlockRecv, 2)
+	gopark(chanparkcommit, unsafe.Pointer(&c.lock), waitReasonChanReceive, traceBlockChanRecv, 2)
 
 	// someone woke us up
 	if mysg != gp.waiting {

src/runtime/debugcall.go

@@ -162,7 +162,7 @@ func debugCallWrap(dispatch uintptr) {
 
 		// Park the calling goroutine.
 		if traceEnabled() {
-			traceGoPark(traceEvGoBlock, 1)
+			traceGoPark(traceBlockDebugCall, 1)
 		}
 		casGToWaiting(gp, _Grunning, waitReasonDebugCall)
 		dropg()

src/runtime/lock_js.go

@@ -114,7 +114,7 @@ func notetsleepg(n *note, ns int64) bool {
 		notesWithTimeout[n] = noteWithTimeout{gp: gp, deadline: deadline}
 		releasem(mp)
 
-		gopark(nil, nil, waitReasonSleep, traceEvNone, 1)
+		gopark(nil, nil, waitReasonSleep, traceBlockSleep, 1)
 
 		clearTimeoutEvent(id) // note might have woken early, clear timeout
 		clearIdleID()
@@ -132,7 +132,7 @@ func notetsleepg(n *note, ns int64) bool {
 		notes[n] = gp
 		releasem(mp)
 
-		gopark(nil, nil, waitReasonZero, traceEvNone, 1)
+		gopark(nil, nil, waitReasonZero, traceBlockGeneric, 1)
 
 		mp = acquirem()
 		delete(notes, n)
@@ -256,7 +256,7 @@ func handleEvent() {
 
 	// wait until all goroutines are idle
 	e.returned = true
-	gopark(nil, nil, waitReasonZero, traceEvNone, 1)
+	gopark(nil, nil, waitReasonZero, traceBlockGeneric, 1)
 
 	events[len(events)-1] = nil
 	events = events[:len(events)-1]

src/runtime/mfinal.go

@@ -190,7 +190,7 @@ func runfinq() {
 		fb := finq
 		finq = nil
 		if fb == nil {
-			gopark(finalizercommit, unsafe.Pointer(&finlock), waitReasonFinalizerWait, traceEvGoBlock, 1)
+			gopark(finalizercommit, unsafe.Pointer(&finlock), waitReasonFinalizerWait, traceBlockSystemGoroutine, 1)
 			continue
 		}
 		argRegs = intArgRegs

src/runtime/mgc.go

@@ -500,7 +500,7 @@ func gcWaitOnMark(n uint32) {
 		// Wait until sweep termination, mark, and mark
 		// termination of cycle N complete.
 		work.sweepWaiters.list.push(getg())
-		goparkunlock(&work.sweepWaiters.lock, waitReasonWaitForGCCycle, traceEvGoBlock, 1)
+		goparkunlock(&work.sweepWaiters.lock, waitReasonWaitForGCCycle, traceBlockUntilGCEnds, 1)
 	}
 }
 
@@ -1315,7 +1315,7 @@ func gcBgMarkWorker() {
 			// Note that at this point, the G may immediately be
 			// rescheduled and may be running.
 			return true
-		}, unsafe.Pointer(node), waitReasonGCWorkerIdle, traceEvGoBlock, 0)
+		}, unsafe.Pointer(node), waitReasonGCWorkerIdle, traceBlockSystemGoroutine, 0)
 
 		// Preemption must not occur here, or another G might see
 		// p.gcMarkWorkerMode.

src/runtime/mgcmark.go

@@ -649,7 +649,7 @@ func gcParkAssist() bool {
 		return false
 	}
 	// Park.
-	goparkunlock(&work.assistQueue.lock, waitReasonGCAssistWait, traceEvGoBlockGC, 2)
+	goparkunlock(&work.assistQueue.lock, waitReasonGCAssistWait, traceBlockGCMarkAssist, 2)
 	return true
 }
 

src/runtime/mgcscavenge.go

@@ -422,7 +422,7 @@ func (s *scavengerState) park() {
 		throw("tried to park scavenger from another goroutine")
 	}
 	s.parked = true
-	goparkunlock(&s.lock, waitReasonGCScavengeWait, traceEvGoBlock, 2)
+	goparkunlock(&s.lock, waitReasonGCScavengeWait, traceBlockSystemGoroutine, 2)
 }
 
 // ready signals to sysmon that the scavenger should be awoken.
@@ -501,7 +501,7 @@ func (s *scavengerState) sleep(worked float64) {
 
 		// Mark ourselves as asleep and go to sleep.
 		s.parked = true
-		goparkunlock(&s.lock, waitReasonSleep, traceEvGoSleep, 2)
+		goparkunlock(&s.lock, waitReasonSleep, traceBlockSleep, 2)
 
 		// How long we actually slept for.
 		slept = nanotime() - start

src/runtime/mgcsweep.go

@@ -277,7 +277,7 @@ func bgsweep(c chan int) {
 	lock(&sweep.lock)
 	sweep.parked = true
 	c <- 1
-	goparkunlock(&sweep.lock, waitReasonGCSweepWait, traceEvGoBlock, 1)
+	goparkunlock(&sweep.lock, waitReasonGCSweepWait, traceBlockGCSweep, 1)
 
 	for {
 		// bgsweep attempts to be a "low priority" goroutine by intentionally
@@ -318,7 +318,7 @@ func bgsweep(c chan int) {
 			continue
 		}
 		sweep.parked = true
-		goparkunlock(&sweep.lock, waitReasonGCSweepWait, traceEvGoBlock, 1)
+		goparkunlock(&sweep.lock, waitReasonGCSweepWait, traceBlockGCSweep, 1)
 	}
 }
 

src/runtime/netpoll.go

@@ -561,7 +561,7 @@ func netpollblock(pd *pollDesc, mode int32, waitio bool) bool {
 	// this is necessary because runtime_pollUnblock/runtime_pollSetDeadline/deadlineimpl
 	// do the opposite: store to closing/rd/wd, publishInfo, load of rg/wg
 	if waitio || netpollcheckerr(pd, mode) == pollNoError {
-		gopark(netpollblockcommit, unsafe.Pointer(gpp), waitReasonIOWait, traceEvGoBlockNet, 5)
+		gopark(netpollblockcommit, unsafe.Pointer(gpp), waitReasonIOWait, traceBlockNet, 5)
 	}
 	// be careful to not lose concurrent pdReady notification
 	old := gpp.Swap(pdNil)

src/runtime/proc.go

@@ -284,7 +284,7 @@ func main() {
 		}
 	}
 	if panicking.Load() != 0 {
-		gopark(nil, nil, waitReasonPanicWait, traceEvGoStop, 1)
+		gopark(nil, nil, waitReasonPanicWait, traceBlockForever, 1)
 	}
 	runExitHooks(0)
 
@@ -319,7 +319,7 @@ func forcegchelper() {
 			throw("forcegc: phase error")
 		}
 		forcegc.idle.Store(true)
-		goparkunlock(&forcegc.lock, waitReasonForceGCIdle, traceEvGoBlock, 1)
+		goparkunlock(&forcegc.lock, waitReasonForceGCIdle, traceBlockSystemGoroutine, 1)
 		// this goroutine is explicitly resumed by sysmon
 		if debug.gctrace > 0 {
 			println("GC forced")
@@ -378,7 +378,7 @@ func goschedIfBusy() {
 // Reason explains why the goroutine has been parked. It is displayed in stack
 // traces and heap dumps. Reasons should be unique and descriptive. Do not
 // re-use reasons, add new ones.
-func gopark(unlockf func(*g, unsafe.Pointer) bool, lock unsafe.Pointer, reason waitReason, traceEv byte, traceskip int) {
+func gopark(unlockf func(*g, unsafe.Pointer) bool, lock unsafe.Pointer, reason waitReason, traceReason traceBlockReason, traceskip int) {
 	if reason != waitReasonSleep {
 		checkTimeouts() // timeouts may expire while two goroutines keep the scheduler busy
 	}
@@ -391,8 +391,8 @@ func gopark(unlockf func(*g, unsafe.Pointer) bool, lock unsafe.Pointer, reason w
 	mp.waitlock = lock
 	mp.waitunlockf = unlockf
 	gp.waitreason = reason
-	mp.waittraceev = traceEv
+	mp.waitTraceBlockReason = traceReason
-	mp.waittraceskip = traceskip
+	mp.waitTraceSkip = traceskip
 	releasem(mp)
 	// can't do anything that might move the G between Ms here.
 	mcall(park_m)
@@ -400,8 +400,8 @@ func gopark(unlockf func(*g, unsafe.Pointer) bool, lock unsafe.Pointer, reason w
 
 // Puts the current goroutine into a waiting state and unlocks the lock.
 // The goroutine can be made runnable again by calling goready(gp).
-func goparkunlock(lock *mutex, reason waitReason, traceEv byte, traceskip int) {
+func goparkunlock(lock *mutex, reason waitReason, traceReason traceBlockReason, traceskip int) {
-	gopark(parkunlock_c, unsafe.Pointer(lock), reason, traceEv, traceskip)
+	gopark(parkunlock_c, unsafe.Pointer(lock), reason, traceReason, traceskip)
 }
 
 func goready(gp *g, traceskip int) {
@@ -3678,7 +3678,7 @@ func park_m(gp *g) {
 	mp := getg().m
 
 	if traceEnabled() {
-		traceGoPark(mp.waittraceev, mp.waittraceskip)
+		traceGoPark(mp.waitTraceBlockReason, mp.waitTraceSkip)
 	}
 
 	// N.B. Not using casGToWaiting here because the waitreason is
@@ -3749,7 +3749,7 @@ func gopreempt_m(gp *g) {
 //go:systemstack
 func preemptPark(gp *g) {
 	if traceEnabled() {
-		traceGoPark(traceEvGoBlock, 0)
+		traceGoPark(traceBlockPreempted, 0)
 	}
 	status := readgstatus(gp)
 	if status&^_Gscan != _Grunning {

src/runtime/runtime2.go

@@ -583,8 +583,8 @@ type m struct {
 	// there's no stack to put them on. That is their sole purpose.
 	waitunlockf          func(*g, unsafe.Pointer) bool
 	waitlock             unsafe.Pointer
-	waittraceev   byte
+	waitTraceBlockReason traceBlockReason
-	waittraceskip int
+	waitTraceSkip        int
 
 	syscalltick uint32
 	freelink    *m // on sched.freem

src/runtime/select.go

@@ -100,7 +100,7 @@ func selparkcommit(gp *g, _ unsafe.Pointer) bool {
 }
 
 func block() {
-	gopark(nil, nil, waitReasonSelectNoCases, traceEvGoStop, 1) // forever
+	gopark(nil, nil, waitReasonSelectNoCases, traceBlockForever, 1) // forever
 }
 
 // selectgo implements the select statement.
@@ -324,7 +324,7 @@ func selectgo(cas0 *scase, order0 *uint16, pc0 *uintptr, nsends, nrecvs int, blo
 	// changes and when we set gp.activeStackChans is not safe for
 	// stack shrinking.
 	gp.parkingOnChan.Store(true)
-	gopark(selparkcommit, nil, waitReasonSelect, traceEvGoBlockSelect, 1)
+	gopark(selparkcommit, nil, waitReasonSelect, traceBlockSelect, 1)
 	gp.activeStackChans = false
 
 	sellock(scases, lockorder)

src/runtime/sema.go

@@ -157,7 +157,7 @@ func semacquire1(addr *uint32, lifo bool, profile semaProfileFlags, skipframes i
 		// Any semrelease after the cansemacquire knows we're waiting
 		// (we set nwait above), so go to sleep.
 		root.queue(addr, s, lifo)
-		goparkunlock(&root.lock, reason, traceEvGoBlockSync, 4+skipframes)
+		goparkunlock(&root.lock, reason, traceBlockSync, 4+skipframes)
 		if s.ticket != 0 || cansemacquire(addr) {
 			break
 		}
@@ -524,7 +524,7 @@ func notifyListWait(l *notifyList, t uint32) {
 		l.tail.next = s
 	}
 	l.tail = s
-	goparkunlock(&l.lock, waitReasonSyncCondWait, traceEvGoBlockCond, 3)
+	goparkunlock(&l.lock, waitReasonSyncCondWait, traceBlockCondWait, 3)
 	if t0 != 0 {
 		blockevent(s.releasetime-t0, 2)
 	}

src/runtime/time.go

@@ -192,7 +192,7 @@ func timeSleep(ns int64) {
 	if t.nextwhen < 0 { // check for overflow.
 		t.nextwhen = maxWhen
 	}
-	gopark(resetForSleep, unsafe.Pointer(t), waitReasonSleep, traceEvGoSleep, 1)
+	gopark(resetForSleep, unsafe.Pointer(t), waitReasonSleep, traceBlockSleep, 1)
 }
 
 // resetForSleep is called after the goroutine is parked for timeSleep.

src/runtime/trace.go

@@ -78,6 +78,35 @@ const (
 	// That means, the max event type value is 63.
 )
 
+// traceBlockReason is an enumeration of reasons a goroutine might block.
+// This is the interface the rest of the runtime uses to tell the
+// tracer why a goroutine blocked. The tracer then propagates this information
+// into the trace however it sees fit.
+//
+// Note that traceBlockReasons should not be compared, since reasons that are
+// distinct by name may *not* be distinct by value.
+type traceBlockReason uint8
+
+// For maximal efficiency, just map the trace block reason directly to a trace
+// event.
+const (
+	traceBlockGeneric         traceBlockReason = traceEvGoBlock
+	traceBlockForever                          = traceEvGoStop
+	traceBlockNet                              = traceEvGoBlockNet
+	traceBlockSelect                           = traceEvGoBlockSelect
+	traceBlockCondWait                         = traceEvGoBlockCond
+	traceBlockSync                             = traceEvGoBlockSync
+	traceBlockChanSend                         = traceEvGoBlockSend
+	traceBlockChanRecv                         = traceEvGoBlockRecv
+	traceBlockGCMarkAssist                     = traceEvGoBlockGC
+	traceBlockGCSweep                          = traceEvGoBlock
+	traceBlockSystemGoroutine                  = traceEvGoBlock
+	traceBlockPreempted                        = traceEvGoBlock
+	traceBlockDebugCall                        = traceEvGoBlock
+	traceBlockUntilGCEnds                      = traceEvGoBlock
+	traceBlockSleep                            = traceEvGoSleep
+)
+
 const (
 	// Timestamps in trace are cputicks/traceTickDiv.
 	// This makes absolute values of timestamp diffs smaller,
@@ -511,7 +540,7 @@ top:
 			}
 
 			return true
-		}, nil, waitReasonTraceReaderBlocked, traceEvGoBlock, 2)
+		}, nil, waitReasonTraceReaderBlocked, traceBlockSystemGoroutine, 2)
 		goto top
 	}
 
@@ -1588,8 +1617,10 @@ func traceGoPreempt() {
 	traceEvent(traceEvGoPreempt, 1)
 }
 
-func traceGoPark(traceEv byte, skip int) {
+func traceGoPark(reason traceBlockReason, skip int) {
-	traceEvent(traceEv, skip)
+	// Convert the block reason directly to a trace event type.
+	// See traceBlockReason for more information.
+	traceEvent(byte(reason), skip)
 }
 
 func traceGoUnpark(gp *g, skip int) {