44 lines
1.6 KiB
Go
44 lines
1.6 KiB
Go
package local
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import (
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"sync"
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clientmodel "github.com/prometheus/client_golang/model"
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)
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// fingerprintLocker allows locking individual fingerprints. To limit the number
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// of mutexes needed for that, only a fixed number of mutexes are
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// allocated. Fingerprints to be locked are assigned to those pre-allocated
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// mutexes by their value. (Note that fingerprints are calculated by a hash
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// function, so that an approximately equal distribution over the mutexes is
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// expected, even without additional hashing of the fingerprint value.)
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// Collisions are not detected. If two fingerprints get assigned to the same
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// mutex, only one of them can be locked at the same time. As long as the number
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// of pre-allocated mutexes is much larger than the number of goroutines
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// requiring a fingerprint lock concurrently, the loss in efficiency is
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// small. However, a goroutine must never lock more than one fingerprint at the
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// same time. (In that case a collision would try to acquire the same mutex
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// twice).
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type fingerprintLocker struct {
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fpMtxs []sync.Mutex
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numFpMtxs uint
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}
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// newFingerprintLocker returns a new fingerprintLocker ready for use.
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func newFingerprintLocker(preallocatedMutexes int) *fingerprintLocker {
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return &fingerprintLocker{
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make([]sync.Mutex, preallocatedMutexes),
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uint(preallocatedMutexes),
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}
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}
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// Lock locks the given fingerprint.
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func (l *fingerprintLocker) Lock(fp clientmodel.Fingerprint) {
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l.fpMtxs[uint(fp)%l.numFpMtxs].Lock()
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}
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// Unlock unlocks the given fingerprint.
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func (l *fingerprintLocker) Unlock(fp clientmodel.Fingerprint) {
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l.fpMtxs[uint(fp)%l.numFpMtxs].Unlock()
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}
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