github.com/bytedance/gopkg@v0.0.0-20240514070511-01b2cbcf35e1/lang/syncx/pool.go (about) 1 // Copyright 2021 ByteDance Inc. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 //go:build !race 16 // +build !race 17 18 package syncx 19 20 import ( 21 "runtime" 22 "sync" 23 "sync/atomic" 24 "unsafe" 25 26 "github.com/bytedance/gopkg/internal/runtimex" 27 ) 28 29 type Pool struct { 30 noCopy noCopy 31 32 local unsafe.Pointer // local fixed-size per-P pool, actual type is [P]poolLocal 33 localSize uintptr // size of the local array 34 35 newSize int32 // mark every time New is executed 36 gcSize int32 // recommended number of gc 37 38 // New optionally specifies a function to generate 39 // a value when Get would otherwise return nil. 40 // It may not be changed concurrently with calls to Get. 41 New func() interface{} 42 // NoGC any objects in this Pool. 43 NoGC bool 44 } 45 46 // noCopy may be embedded into structs which must not be copied 47 // after the first use. 48 // 49 // See https://golang.org/issues/8005#issuecomment-190753527 50 // for details. 51 type noCopy struct{} 52 53 // Lock is a no-op used by -copylocks checker from `go vet`. 54 func (*noCopy) Lock() {} 55 func (*noCopy) Unlock() {} 56 57 const blockSize = 256 58 59 type block [blockSize]interface{} 60 61 const shared = 0 62 const unused = 1 63 64 // Local per-P Pool appendix. 65 type poolLocalInternal struct { 66 pidx int // idx of private 67 private *block // Can be used only by the respective P. 68 // Local P can pushHead/popHead; any P can popTail. 69 // 1 is shared, 2 is unused 70 shared [2]poolChain 71 } 72 73 type poolLocal struct { 74 poolLocalInternal 75 // Prevents false sharing on widespread platforms with 76 // 128 mod (cache line size) = 0 . 77 pad [128 - unsafe.Sizeof(poolLocalInternal{})%128]byte 78 } 79 80 // Put adds x to the pool. 81 func (p *Pool) Put(x interface{}) { 82 if x == nil { 83 return 84 } 85 l, pid := p.pin() 86 if l.pidx >= blockSize { 87 l.shared[shared].pushHead(l.private) 88 l.pidx, l.private = 0, nil 89 } 90 if l.private == nil { 91 l.private, _ = l.shared[unused].popHead() 92 if l.private == nil { 93 l.private = p.getSlow(pid, unused) 94 } 95 if l.private == nil { 96 l.private = &block{} 97 } 98 } 99 l.private[l.pidx] = x 100 l.pidx++ 101 x = nil 102 runtimex.Unpin() 103 } 104 105 // Get selects an arbitrary item from the Pool, removes it from the 106 // Pool, and returns it to the caller. 107 // Get may choose to ignore the pool and treat it as empty. 108 // Callers should not assume any relation between values passed to Put and 109 // the values returned by Get. 110 // 111 // If Get would otherwise return nil and p.New is non-nil, Get returns 112 // the result of calling p.New. 113 func (p *Pool) Get() (x interface{}) { 114 l, pid := p.pin() 115 if l.pidx > 0 { 116 l.pidx-- 117 x = l.private[l.pidx] 118 l.private[l.pidx] = nil 119 } 120 if x == nil { 121 // Try to pop the head of the local shard. We prefer 122 // the head over the tail for temporal locality of 123 // reuse. 124 var b, _ = l.shared[shared].popHead() 125 if b == nil { 126 b = p.getSlow(pid, shared) 127 } 128 if b != nil { 129 if l.private != nil { 130 l.shared[unused].pushHead(l.private) 131 } 132 l.private = b 133 l.pidx = blockSize - 1 134 x = l.private[l.pidx] 135 l.private[l.pidx] = nil 136 } 137 } 138 runtimex.Unpin() 139 if x == nil && p.New != nil { 140 atomic.AddInt32(&p.newSize, 1) 141 x = p.New() 142 } 143 return x 144 } 145 146 func (p *Pool) getSlow(pid int, idx int) *block { 147 // See the comment in pin regarding ordering of the loads. 148 size := atomic.LoadUintptr(&p.localSize) // load-acquire 149 locals := p.local // load-consume 150 // Try to steal one element from other procs. 151 for i := 0; i < int(size); i++ { 152 l := indexLocal(locals, (pid+i+1)%int(size)) 153 if x, _ := l.shared[idx].popTail(); x != nil { 154 return x 155 } 156 } 157 return nil 158 } 159 160 // pin pins the current goroutine to P, disables preemption and 161 // returns poolLocal pool for the P and the P's id. 162 // Caller must call runtime_procUnpin() when done with the pool. 163 func (p *Pool) pin() (*poolLocal, int) { 164 pid := runtimex.Pin() 165 // In pinSlow we store to local and then to localSize, here we load in opposite order. 166 // Since we've disabled preemption, GC cannot happen in between. 167 // Thus here we must observe local at least as large localSize. 168 // We can observe a newSize/larger local, it is fine (we must observe its zero-initialized-ness). 169 s := atomic.LoadUintptr(&p.localSize) // load-acquire 170 l := p.local // load-consume 171 if uintptr(pid) < s { 172 return indexLocal(l, pid), pid 173 } 174 return p.pinSlow() 175 } 176 177 func (p *Pool) pinSlow() (*poolLocal, int) { 178 // Retry under the mutex. 179 // Can not lock the mutex while pinned. 180 runtimex.Unpin() 181 allPoolsMu.Lock() 182 defer allPoolsMu.Unlock() 183 pid := runtimex.Pin() 184 // poolCleanup won't be called while we are pinned. 185 s := p.localSize 186 l := p.local 187 if uintptr(pid) < s { 188 return indexLocal(l, pid), pid 189 } 190 if p.local == nil { 191 allPools = append(allPools, p) 192 } 193 // If GOMAXPROCS changes between GCs, we re-allocate the array and lose the old one. 194 size := runtime.GOMAXPROCS(0) 195 local := make([]poolLocal, size) 196 atomic.StorePointer(&p.local, unsafe.Pointer(&local[0])) // store-release 197 atomic.StoreUintptr(&p.localSize, uintptr(size)) // store-release 198 return &local[pid], pid 199 } 200 201 // GC will follow these rules: 202 // 1. Mark the tag `newSize`, if `newSize` exists this time, skip GC. 203 // 2. Calculate the current size, mark as `newSize`. 204 // 3. if `newSize` < `oldSize`, skip GC. 205 // 4. GC size is oldSize/2, the real GC is to throw away a few poolLocals directly. 206 func (p *Pool) gc() { 207 if p.NoGC { 208 return 209 } 210 // 1. check newSize 211 if p.newSize > 0 { 212 p.newSize = 0 213 return 214 } 215 var newSize int32 216 for i := 0; i < int(p.localSize); i++ { 217 l := indexLocal(p.local, i) 218 newSize += l.shared[shared].size 219 } 220 // 2. if new < old; old = new 221 if newSize < p.gcSize { 222 p.gcSize = newSize 223 return 224 } 225 // 3. if new < procs; return 226 if newSize <= int32(p.localSize) { 227 p.gcSize = newSize 228 return 229 } 230 // 4. gc old/2 231 var gcSize int32 232 for i := 0; i < int(p.localSize) && gcSize < p.gcSize/2; i++ { 233 l := indexLocal(p.local, i) 234 gcSize += l.shared[shared].size 235 l.shared[shared].size, l.shared[shared].head, l.shared[shared].tail = 0, nil, nil 236 l.shared[unused].size, l.shared[unused].head, l.shared[unused].tail = 0, nil, nil 237 } 238 p.gcSize = newSize - gcSize 239 } 240 241 var ( 242 allPoolsMu sync.Mutex 243 period int 244 // allPools is the set of pools that have non-empty primary 245 // caches. Protected by either 1) allPoolsMu and pinning or 2) 246 // STW. 247 allPools []*Pool 248 ) 249 250 // GC will be executed every 4 cycles 251 func poolCleanup() { 252 runtime_poolCleanup() 253 period++ 254 if period&0x4 == 0 { 255 return 256 } 257 // This function is called with the world stopped, at the beginning of a garbage collection. 258 // It must not allocate and probably should not call any runtime functions. 259 260 // Because the world is stopped, no pool user can be in a 261 // pinned section (in effect, this has all Ps pinned). 262 263 // Move primary cache to victim cache. 264 for _, p := range allPools { 265 p.gc() 266 } 267 } 268 269 func init() { 270 // FIXME: The linkname here is risky. 271 // If Go renames these func officially, we need to synchronize here, otherwise it may cause OOM. 272 runtime_registerPoolCleanup(poolCleanup) 273 } 274 275 func indexLocal(l unsafe.Pointer, i int) *poolLocal { 276 lp := unsafe.Pointer(uintptr(l) + uintptr(i)*unsafe.Sizeof(poolLocal{})) 277 return (*poolLocal)(lp) 278 }