112 lines
2.6 KiB
Go
112 lines
2.6 KiB
Go
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package util
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import "sync"
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import (
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"errors"
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"sync/atomic"
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)
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// ErrorNoSuchLock is returned when the requested lock does not exist
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var ErrorNoSuchLock = errors.New("no such lock")
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// InMemoryLockRegistry provides a locking mechanism based on the passed in reference name
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type InMemoryLockRegistry struct {
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mu sync.Mutex
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locks map[string]*lockCtr
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}
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// lockCtr is used by InMemoryLockRegistry to represent a lock with a given name.
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type lockCtr struct {
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mu sync.Mutex
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// waiters is the number of waiters waiting to acquire the lock
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// this is int32 instead of uint32, so we can add `-1` in `dec()`
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waiters int32
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}
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// inc increments the number of waiters waiting for the lock
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func (l *lockCtr) inc() {
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atomic.AddInt32(&l.waiters, 1)
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}
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// dec decrements the number of waiters waiting on the lock
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func (l *lockCtr) dec() {
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atomic.AddInt32(&l.waiters, -1)
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}
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// count gets the current number of waiters
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func (l *lockCtr) count() int32 {
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return atomic.LoadInt32(&l.waiters)
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}
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// Lock locks the mutex
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func (l *lockCtr) Lock() {
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l.mu.Lock()
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}
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// Unlock unlocks the mutex
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func (l *lockCtr) Unlock() {
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l.mu.Unlock()
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}
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// NewInMemoryLockRegistry creates a new InMemoryLockRegistry
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func NewInMemoryLockRegistry() *InMemoryLockRegistry {
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return &InMemoryLockRegistry{
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locks: make(map[string]*lockCtr),
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}
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}
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// Clear clears all locks by initializing a new map
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func (l *InMemoryLockRegistry) Clear() {
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l.locks = make(map[string]*lockCtr)
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}
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// Exists exists a lock by name
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func (l *InMemoryLockRegistry) Exists(name string) bool {
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_, exists := l.locks[name]
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return exists
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}
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// Lock locks a mutex with the given name. If it doesn't exist, one is created
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func (l *InMemoryLockRegistry) Lock(name string) {
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l.mu.Lock()
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if l.locks == nil {
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l.locks = make(map[string]*lockCtr)
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}
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nameLock, exists := l.locks[name]
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if !exists {
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nameLock = &lockCtr{}
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l.locks[name] = nameLock
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}
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// increment the nameLock waiters while inside the main mutex
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// this makes sure that the lock isn't deleted if `Lock` and `Unlock` are called concurrently
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nameLock.inc()
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l.mu.Unlock()
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// Lock the nameLock outside the main mutex, so we don't block other operations
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// once locked then we can decrement the number of waiters for this lock
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nameLock.Lock()
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nameLock.dec()
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}
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// Unlock unlocks the mutex with the given name
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// If the given lock is not being waited on by any other callers, it is deleted
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func (l *InMemoryLockRegistry) Unlock(name string) error {
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l.mu.Lock()
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nameLock, exists := l.locks[name]
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if !exists {
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l.mu.Unlock()
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return ErrorNoSuchLock
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}
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if nameLock.count() == 0 {
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delete(l.locks, name)
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}
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nameLock.Unlock()
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l.mu.Unlock()
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return nil
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}
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