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91 lines
2.4 KiB
Go
91 lines
2.4 KiB
Go
package multimutex
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import (
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"fmt"
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"sync"
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"github.com/lightningnetwork/lnd/lntypes"
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)
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// HashMutex is a struct that keeps track of a set of mutexes with a given hash.
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// It can be used for making sure only one goroutine gets given the mutex per
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// hash.
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type HashMutex struct {
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// mutexes is a map of hashes to a cntMutex. The cntMutex for
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// a given hash will hold the mutex to be used by all
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// callers requesting access for the hash, in addition to
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// the count of callers.
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mutexes map[lntypes.Hash]*cntMutex
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// mapMtx is used to give synchronize concurrent access
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// to the mutexes map.
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mapMtx sync.Mutex
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}
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// NewHashMutex creates a new Mutex.
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func NewHashMutex() *HashMutex {
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return &HashMutex{
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mutexes: make(map[lntypes.Hash]*cntMutex),
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}
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}
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// Lock locks the mutex by the given hash. If the mutex is already
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// locked by this hash, Lock blocks until the mutex is available.
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func (c *HashMutex) Lock(hash lntypes.Hash) {
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c.mapMtx.Lock()
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mtx, ok := c.mutexes[hash]
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if ok {
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// If the mutex already existed in the map, we
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// increment its counter, to indicate that there
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// now is one more goroutine waiting for it.
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mtx.cnt++
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} else {
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// If it was not in the map, it means no other
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// goroutine has locked the mutex for this hash,
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// and we can create a new mutex with count 1
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// and add it to the map.
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mtx = &cntMutex{
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cnt: 1,
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}
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c.mutexes[hash] = mtx
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}
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c.mapMtx.Unlock()
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// Acquire the mutex for this hash.
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mtx.Lock()
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}
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// Unlock unlocks the mutex by the given hash. It is a run-time
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// error if the mutex is not locked by the hash on entry to Unlock.
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func (c *HashMutex) Unlock(hash lntypes.Hash) {
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// Since we are done with all the work for this
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// update, we update the map to reflect that.
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c.mapMtx.Lock()
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mtx, ok := c.mutexes[hash]
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if !ok {
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// The mutex not existing in the map means
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// an unlock for an hash not currently locked
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// was attempted.
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panic(fmt.Sprintf("double unlock for hash %v",
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hash))
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}
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// Decrement the counter. If the count goes to
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// zero, it means this caller was the last one
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// to wait for the mutex, and we can delete it
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// from the map. We can do this safely since we
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// are under the mapMtx, meaning that all other
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// goroutines waiting for the mutex already
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// have incremented it, or will create a new
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// mutex when they get the mapMtx.
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mtx.cnt--
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if mtx.cnt == 0 {
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delete(c.mutexes, hash)
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}
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c.mapMtx.Unlock()
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// Unlock the mutex for this hash.
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mtx.Unlock()
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}
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