forked from mirrors/gotosocial
105 lines
2.2 KiB
Go
105 lines
2.2 KiB
Go
package mutexes
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import (
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"sync"
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)
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// MutexMap is a structure that allows having a map of self-evicting mutexes
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// by key. You do not need to worry about managing the contents of the map,
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// only requesting RLock/Lock for keys, and ensuring to call the returned
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// unlock functions.
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type MutexMap struct {
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// NOTE:
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// Individual keyed mutexes should ONLY ever
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// be locked within the protection of the outer
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// mapMu lock. If you lock these outside the
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// protection of this, there is a chance for
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// deadlocks
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mus map[string]RWMutex
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mapMu sync.Mutex
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pool sync.Pool
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}
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// NewMap returns a new MutexMap instance based on supplied
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// RWMutex allocator function, nil implies use default
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func NewMap(newFn func() RWMutex) MutexMap {
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if newFn == nil {
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newFn = NewRW
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}
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return MutexMap{
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mus: make(map[string]RWMutex),
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mapMu: sync.Mutex{},
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pool: sync.Pool{
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New: func() interface{} {
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return newFn()
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},
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},
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}
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}
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func (mm *MutexMap) evict(key string, mu RWMutex) {
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// Acquire map lock
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mm.mapMu.Lock()
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// Toggle mutex lock to
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// ensure it is unused
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unlock := mu.Lock()
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unlock()
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// Delete mutex key
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delete(mm.mus, key)
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mm.mapMu.Unlock()
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// Release to pool
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mm.pool.Put(mu)
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}
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// RLock acquires a mutex read lock for supplied key, returning an RUnlock function
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func (mm *MutexMap) RLock(key string) func() {
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return mm.getLock(key, func(mu RWMutex) func() {
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return mu.RLock()
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})
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}
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// Lock acquires a mutex lock for supplied key, returning an Unlock function
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func (mm *MutexMap) Lock(key string) func() {
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return mm.getLock(key, func(mu RWMutex) func() {
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return mu.Lock()
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})
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}
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func (mm *MutexMap) getLock(key string, doLock func(RWMutex) func()) func() {
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// Get map lock
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mm.mapMu.Lock()
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// Look for mutex
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mu, ok := mm.mus[key]
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if ok {
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// Lock and return
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// its unlocker func
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unlock := doLock(mu)
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mm.mapMu.Unlock()
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return unlock
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}
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// Note: even though the mutex data structure is
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// small, benchmarking does actually show that pooled
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// alloc of mutexes here is faster
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// Acquire mu + add
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mu = mm.pool.Get().(RWMutex)
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mm.mus[key] = mu
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// Lock mutex + unlock map
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unlockFn := doLock(mu)
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mm.mapMu.Unlock()
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return func() {
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// Unlock mutex
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unlockFn()
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// Release function
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go mm.evict(key, mu)
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}
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}
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