Copyright 2020 The Go Authors. All rights reserved. Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
This file records the static ranks of the locks in the runtime. If a lock is not given a rank, then it is assumed to be a leaf lock, which means no other lock can be acquired while it is held. Therefore, leaf locks do not need to be given an explicit rank. We list all of the architecture-independent leaf locks for documentation purposes, but don't list any of the architecture-dependent locks (which are all leaf locks). debugLock is ignored for ranking, since it is used when printing out lock ranking errors. lockInit(l *mutex, rank int) is used to set the rank of lock before it is used. If there is no clear place to initialize a lock, then the rank of a lock can be specified during the lock call itself via lockWithrank(l *mutex, rank int). Besides the static lock ranking (which is a total ordering of the locks), we also represent and enforce the actual partial order among the locks in the arcs[] array below. That is, if it is possible that lock B can be acquired when lock A is the previous acquired lock that is still held, then there should be an entry for A in arcs[B][]. We will currently fail not only if the total order (the lock ranking) is violated, but also if there is a missing entry in the partial order.

package runtime

type lockRank int
Constants representing the lock rank of the architecture-independent locks in the runtime. Locks with lower rank must be taken before locks with higher rank.
const (
	lockRankDummy lockRank = iota
Locks held above sched
	lockRankSysmon
	lockRankScavenge
	lockRankForcegc
	lockRankSweepWaiters
	lockRankAssistQueue
	lockRankCpuprof
	lockRankSweep

	lockRankPollDesc
	lockRankSched
	lockRankDeadlock
	lockRankPanic
	lockRankAllg
	lockRankAllp

	lockRankTimers // Multiple timers locked simultaneously in destroy()
	lockRankItab
	lockRankReflectOffs
	lockRankHchan // Multiple hchans acquired in lock order in syncadjustsudogs()
	lockRankFin
	lockRankNotifyList
	lockRankTraceBuf
	lockRankTraceStrings
	lockRankMspanSpecial
	lockRankProf
	lockRankGcBitsArenas
	lockRankRoot
	lockRankTrace
	lockRankTraceStackTab
	lockRankNetpollInit

	lockRankRwmutexW
	lockRankRwmutexR

	lockRankSpanSetSpine
	lockRankGscan
	lockRankStackpool
	lockRankStackLarge
	lockRankDefer
	lockRankSudog
Memory-related non-leaf locks
	lockRankWbufSpans
	lockRankMheap
	lockRankMheapSpecial
Memory-related leaf locks
	lockRankGlobalAlloc
Other leaf locks
Generally, hchan must be acquired before gscan. But in one specific case (in syncadjustsudogs from markroot after the g has been suspended by suspendG), we allow gscan to be acquired, and then an hchan lock. To allow this case, we get this lockRankHchanLeaf rank in syncadjustsudogs(), rather than lockRankHchan. By using this special rank, we don't allow any further locks to be acquired other than more hchan locks.
	lockRankHchanLeaf
Leaf locks with no dependencies, so these constants are not actually used anywhere. There are other architecture-dependent leaf locks as well.
	lockRankNewmHandoff
	lockRankDebugPtrmask
	lockRankFaketimeState
	lockRankTicks
	lockRankRaceFini
	lockRankPollCache
	lockRankDebug
)
lockRankLeafRank is the rank of lock that does not have a declared rank, and hence is a leaf lock.
const lockRankLeafRank lockRank = 1000
lockNames gives the names associated with each of the above ranks
var lockNames = []string{
	lockRankDummy: "",

	lockRankSysmon:       "sysmon",
	lockRankScavenge:     "scavenge",
	lockRankForcegc:      "forcegc",
	lockRankSweepWaiters: "sweepWaiters",
	lockRankAssistQueue:  "assistQueue",
	lockRankCpuprof:      "cpuprof",
	lockRankSweep:        "sweep",

	lockRankPollDesc: "pollDesc",
	lockRankSched:    "sched",
	lockRankDeadlock: "deadlock",
	lockRankPanic:    "panic",
	lockRankAllg:     "allg",
	lockRankAllp:     "allp",

	lockRankTimers:      "timers",
	lockRankItab:        "itab",
	lockRankReflectOffs: "reflectOffs",

	lockRankHchan:         "hchan",
	lockRankFin:           "fin",
	lockRankNotifyList:    "notifyList",
	lockRankTraceBuf:      "traceBuf",
	lockRankTraceStrings:  "traceStrings",
	lockRankMspanSpecial:  "mspanSpecial",
	lockRankProf:          "prof",
	lockRankGcBitsArenas:  "gcBitsArenas",
	lockRankRoot:          "root",
	lockRankTrace:         "trace",
	lockRankTraceStackTab: "traceStackTab",
	lockRankNetpollInit:   "netpollInit",

	lockRankRwmutexW: "rwmutexW",
	lockRankRwmutexR: "rwmutexR",

	lockRankSpanSetSpine: "spanSetSpine",
	lockRankGscan:        "gscan",
	lockRankStackpool:    "stackpool",
	lockRankStackLarge:   "stackLarge",
	lockRankDefer:        "defer",
	lockRankSudog:        "sudog",

	lockRankWbufSpans:    "wbufSpans",
	lockRankMheap:        "mheap",
	lockRankMheapSpecial: "mheapSpecial",

	lockRankGlobalAlloc: "globalAlloc.mutex",

	lockRankGFree:     "gFree",
	lockRankHchanLeaf: "hchanLeaf",

	lockRankNewmHandoff:   "newmHandoff.lock",
	lockRankDebugPtrmask:  "debugPtrmask.lock",
	lockRankFaketimeState: "faketimeState.lock",
	lockRankTicks:         "ticks.lock",
	lockRankRaceFini:      "raceFiniLock",
	lockRankPollCache:     "pollCache.lock",
	lockRankDebug:         "debugLock",
}

func ( lockRank) () string {
	if  == 0 {
		return "UNKNOWN"
	}
	if  == lockRankLeafRank {
		return "LEAF"
	}
	return lockNames[]
}
lockPartialOrder is a partial order among the various lock types, listing the immediate ordering that has actually been observed in the runtime. Each entry (which corresponds to a particular lock rank) specifies the list of locks that can already be held immediately "above" it. So, for example, the lockRankSched entry shows that all the locks preceding it in rank can actually be held. The allp lock shows that only the sysmon or sched lock can be held immediately above it when it is acquired.
var lockPartialOrder [][]lockRank = [][]lockRank{
	lockRankDummy:         {},
	lockRankSysmon:        {},
	lockRankScavenge:      {lockRankSysmon},
	lockRankForcegc:       {lockRankSysmon},
	lockRankSweepWaiters:  {},
	lockRankAssistQueue:   {},
	lockRankCpuprof:       {},
	lockRankSweep:         {},
	lockRankPollDesc:      {},
	lockRankSched:         {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankCpuprof, lockRankSweep, lockRankPollDesc},
	lockRankDeadlock:      {lockRankDeadlock},
	lockRankPanic:         {lockRankDeadlock},
	lockRankAllg:          {lockRankSysmon, lockRankSched, lockRankPanic},
	lockRankAllp:          {lockRankSysmon, lockRankSched},
	lockRankTimers:        {lockRankSysmon, lockRankScavenge, lockRankSched, lockRankAllp, lockRankPollDesc, lockRankTimers},
	lockRankItab:          {},
	lockRankReflectOffs:   {lockRankItab},
	lockRankHchan:         {lockRankScavenge, lockRankSweep, lockRankHchan},
	lockRankFin:           {lockRankSysmon, lockRankScavenge, lockRankSched, lockRankAllg, lockRankTimers, lockRankHchan},
	lockRankNotifyList:    {},
	lockRankTraceBuf:      {lockRankSysmon, lockRankScavenge},
	lockRankTraceStrings:  {lockRankTraceBuf},
	lockRankMspanSpecial:  {lockRankSysmon, lockRankScavenge, lockRankAssistQueue, lockRankCpuprof, lockRankSweep, lockRankSched, lockRankAllg, lockRankAllp, lockRankTimers, lockRankItab, lockRankReflectOffs, lockRankHchan, lockRankNotifyList, lockRankTraceBuf, lockRankTraceStrings},
	lockRankProf:          {lockRankSysmon, lockRankScavenge, lockRankAssistQueue, lockRankCpuprof, lockRankSweep, lockRankSched, lockRankAllg, lockRankAllp, lockRankTimers, lockRankItab, lockRankReflectOffs, lockRankNotifyList, lockRankTraceBuf, lockRankTraceStrings, lockRankHchan},
	lockRankGcBitsArenas:  {lockRankSysmon, lockRankScavenge, lockRankAssistQueue, lockRankCpuprof, lockRankSched, lockRankAllg, lockRankTimers, lockRankItab, lockRankReflectOffs, lockRankNotifyList, lockRankTraceBuf, lockRankTraceStrings, lockRankHchan},
	lockRankRoot:          {},
	lockRankTrace:         {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankAssistQueue, lockRankSched, lockRankHchan, lockRankTraceBuf, lockRankTraceStrings, lockRankRoot, lockRankSweep},
	lockRankTraceStackTab: {lockRankScavenge, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankSched, lockRankAllg, lockRankTimers, lockRankHchan, lockRankFin, lockRankNotifyList, lockRankTraceBuf, lockRankTraceStrings, lockRankRoot, lockRankTrace},
	lockRankNetpollInit:   {lockRankTimers},

	lockRankRwmutexW: {},
	lockRankRwmutexR: {lockRankSysmon, lockRankRwmutexW},

	lockRankSpanSetSpine: {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankAssistQueue, lockRankCpuprof, lockRankSweep, lockRankPollDesc, lockRankSched, lockRankAllg, lockRankAllp, lockRankTimers, lockRankItab, lockRankReflectOffs, lockRankNotifyList, lockRankTraceBuf, lockRankTraceStrings, lockRankHchan},
	lockRankGscan:        {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankCpuprof, lockRankSweep, lockRankSched, lockRankTimers, lockRankItab, lockRankReflectOffs, lockRankHchan, lockRankFin, lockRankTraceBuf, lockRankTraceStrings, lockRankRoot, lockRankNotifyList, lockRankProf, lockRankGcBitsArenas, lockRankTrace, lockRankTraceStackTab, lockRankNetpollInit, lockRankSpanSetSpine},
	lockRankStackpool:    {lockRankSysmon, lockRankScavenge, lockRankSweepWaiters, lockRankAssistQueue, lockRankCpuprof, lockRankSweep, lockRankSched, lockRankPollDesc, lockRankTimers, lockRankItab, lockRankReflectOffs, lockRankHchan, lockRankFin, lockRankNotifyList, lockRankTraceBuf, lockRankTraceStrings, lockRankProf, lockRankGcBitsArenas, lockRankRoot, lockRankTrace, lockRankTraceStackTab, lockRankNetpollInit, lockRankRwmutexR, lockRankSpanSetSpine, lockRankGscan},
	lockRankStackLarge:   {lockRankSysmon, lockRankAssistQueue, lockRankSched, lockRankItab, lockRankHchan, lockRankProf, lockRankGcBitsArenas, lockRankRoot, lockRankSpanSetSpine, lockRankGscan},
	lockRankDefer:        {},
	lockRankSudog:        {lockRankNotifyList, lockRankHchan},
	lockRankWbufSpans:    {lockRankSysmon, lockRankScavenge, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankSched, lockRankAllg, lockRankPollDesc, lockRankTimers, lockRankItab, lockRankReflectOffs, lockRankHchan, lockRankFin, lockRankNotifyList, lockRankTraceStrings, lockRankMspanSpecial, lockRankProf, lockRankRoot, lockRankGscan, lockRankDefer, lockRankSudog},
	lockRankMheap:        {lockRankSysmon, lockRankScavenge, lockRankSweepWaiters, lockRankAssistQueue, lockRankCpuprof, lockRankSweep, lockRankSched, lockRankAllg, lockRankAllp, lockRankFin, lockRankPollDesc, lockRankTimers, lockRankItab, lockRankReflectOffs, lockRankNotifyList, lockRankTraceBuf, lockRankTraceStrings, lockRankHchan, lockRankMspanSpecial, lockRankProf, lockRankGcBitsArenas, lockRankRoot, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankDefer, lockRankSudog, lockRankWbufSpans, lockRankSpanSetSpine},
	lockRankMheapSpecial: {lockRankSysmon, lockRankScavenge, lockRankAssistQueue, lockRankCpuprof, lockRankSweep, lockRankSched, lockRankAllg, lockRankAllp, lockRankTimers, lockRankItab, lockRankReflectOffs, lockRankNotifyList, lockRankTraceBuf, lockRankTraceStrings, lockRankHchan},
	lockRankGlobalAlloc:  {lockRankProf, lockRankSpanSetSpine, lockRankMheap, lockRankMheapSpecial},

	lockRankGFree:     {lockRankSched},
	lockRankHchanLeaf: {lockRankGscan, lockRankHchanLeaf},

	lockRankNewmHandoff:   {},
	lockRankDebugPtrmask:  {},
	lockRankFaketimeState: {},
	lockRankTicks:         {},
	lockRankRaceFini:      {},
	lockRankPollCache:     {},
	lockRankDebug:         {},