1// Copyright 2011 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// +build dragonfly freebsd linux 6 7package runtime 8 9import ( 10 "runtime/internal/atomic" 11 "unsafe" 12) 13 14// For gccgo, while we still have C runtime code, use go:linkname to 15// export some functions. 16// 17//go:linkname lock 18//go:linkname unlock 19//go:linkname noteclear 20//go:linkname notewakeup 21//go:linkname notesleep 22//go:linkname notetsleep 23//go:linkname notetsleepg 24 25// This implementation depends on OS-specific implementations of 26// 27// futexsleep(addr *uint32, val uint32, ns int64) 28// Atomically, 29// if *addr == val { sleep } 30// Might be woken up spuriously; that's allowed. 31// Don't sleep longer than ns; ns < 0 means forever. 32// 33// futexwakeup(addr *uint32, cnt uint32) 34// If any procs are sleeping on addr, wake up at most cnt. 35 36const ( 37 mutex_unlocked = 0 38 mutex_locked = 1 39 mutex_sleeping = 2 40 41 active_spin = 4 42 active_spin_cnt = 30 43 passive_spin = 1 44) 45 46// Possible lock states are mutex_unlocked, mutex_locked and mutex_sleeping. 47// mutex_sleeping means that there is presumably at least one sleeping thread. 48// Note that there can be spinning threads during all states - they do not 49// affect mutex's state. 50 51// We use the uintptr mutex.key and note.key as a uint32. 52//go:nosplit 53func key32(p *uintptr) *uint32 { 54 return (*uint32)(unsafe.Pointer(p)) 55} 56 57func lock(l *mutex) { 58 gp := getg() 59 60 if gp.m.locks < 0 { 61 throw("runtime·lock: lock count") 62 } 63 gp.m.locks++ 64 65 // Speculative grab for lock. 66 v := atomic.Xchg(key32(&l.key), mutex_locked) 67 if v == mutex_unlocked { 68 return 69 } 70 71 // wait is either MUTEX_LOCKED or MUTEX_SLEEPING 72 // depending on whether there is a thread sleeping 73 // on this mutex. If we ever change l->key from 74 // MUTEX_SLEEPING to some other value, we must be 75 // careful to change it back to MUTEX_SLEEPING before 76 // returning, to ensure that the sleeping thread gets 77 // its wakeup call. 78 wait := v 79 80 // On uniprocessors, no point spinning. 81 // On multiprocessors, spin for ACTIVE_SPIN attempts. 82 spin := 0 83 if ncpu > 1 { 84 spin = active_spin 85 } 86 for { 87 // Try for lock, spinning. 88 for i := 0; i < spin; i++ { 89 for l.key == mutex_unlocked { 90 if atomic.Cas(key32(&l.key), mutex_unlocked, wait) { 91 return 92 } 93 } 94 procyield(active_spin_cnt) 95 } 96 97 // Try for lock, rescheduling. 98 for i := 0; i < passive_spin; i++ { 99 for l.key == mutex_unlocked { 100 if atomic.Cas(key32(&l.key), mutex_unlocked, wait) { 101 return 102 } 103 } 104 osyield() 105 } 106 107 // Sleep. 108 v = atomic.Xchg(key32(&l.key), mutex_sleeping) 109 if v == mutex_unlocked { 110 return 111 } 112 wait = mutex_sleeping 113 futexsleep(key32(&l.key), mutex_sleeping, -1) 114 } 115} 116 117func unlock(l *mutex) { 118 v := atomic.Xchg(key32(&l.key), mutex_unlocked) 119 if v == mutex_unlocked { 120 throw("unlock of unlocked lock") 121 } 122 if v == mutex_sleeping { 123 futexwakeup(key32(&l.key), 1) 124 } 125 126 gp := getg() 127 gp.m.locks-- 128 if gp.m.locks < 0 { 129 throw("runtime·unlock: lock count") 130 } 131 // if gp.m.locks == 0 && gp.preempt { // restore the preemption request in case we've cleared it in newstack 132 // gp.stackguard0 = stackPreempt 133 // } 134} 135 136// One-time notifications. 137func noteclear(n *note) { 138 n.key = 0 139} 140 141func notewakeup(n *note) { 142 old := atomic.Xchg(key32(&n.key), 1) 143 if old != 0 { 144 print("notewakeup - double wakeup (", old, ")\n") 145 throw("notewakeup - double wakeup") 146 } 147 futexwakeup(key32(&n.key), 1) 148} 149 150func notesleep(n *note) { 151 gp := getg() 152 if gp != gp.m.g0 { 153 throw("notesleep not on g0") 154 } 155 ns := int64(-1) 156 if *cgo_yield != nil { 157 // Sleep for an arbitrary-but-moderate interval to poll libc interceptors. 158 ns = 10e6 159 } 160 for atomic.Load(key32(&n.key)) == 0 { 161 gp.m.blocked = true 162 futexsleep(key32(&n.key), 0, ns) 163 if *cgo_yield != nil { 164 asmcgocall(*cgo_yield, nil) 165 } 166 gp.m.blocked = false 167 } 168} 169 170// May run with m.p==nil if called from notetsleep, so write barriers 171// are not allowed. 172// 173//go:nosplit 174//go:nowritebarrier 175func notetsleep_internal(n *note, ns int64) bool { 176 gp := getg() 177 178 if ns < 0 { 179 if *cgo_yield != nil { 180 // Sleep for an arbitrary-but-moderate interval to poll libc interceptors. 181 ns = 10e6 182 } 183 for atomic.Load(key32(&n.key)) == 0 { 184 gp.m.blocked = true 185 futexsleep(key32(&n.key), 0, ns) 186 if *cgo_yield != nil { 187 asmcgocall(*cgo_yield, nil) 188 } 189 gp.m.blocked = false 190 } 191 return true 192 } 193 194 if atomic.Load(key32(&n.key)) != 0 { 195 return true 196 } 197 198 deadline := nanotime() + ns 199 for { 200 if *cgo_yield != nil && ns > 10e6 { 201 ns = 10e6 202 } 203 gp.m.blocked = true 204 futexsleep(key32(&n.key), 0, ns) 205 if *cgo_yield != nil { 206 asmcgocall(*cgo_yield, nil) 207 } 208 gp.m.blocked = false 209 if atomic.Load(key32(&n.key)) != 0 { 210 break 211 } 212 now := nanotime() 213 if now >= deadline { 214 break 215 } 216 ns = deadline - now 217 } 218 return atomic.Load(key32(&n.key)) != 0 219} 220 221func notetsleep(n *note, ns int64) bool { 222 gp := getg() 223 if gp != gp.m.g0 && gp.m.preemptoff != "" { 224 throw("notetsleep not on g0") 225 } 226 227 return notetsleep_internal(n, ns) 228} 229 230// same as runtime·notetsleep, but called on user g (not g0) 231// calls only nosplit functions between entersyscallblock/exitsyscall 232func notetsleepg(n *note, ns int64) bool { 233 gp := getg() 234 if gp == gp.m.g0 { 235 throw("notetsleepg on g0") 236 } 237 238 entersyscallblock() 239 ok := notetsleep_internal(n, ns) 240 exitsyscall() 241 return ok 242} 243 244func beforeIdle(int64) bool { 245 return false 246} 247 248func checkTimeouts() {} 249