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package mutexkv
import (
"log"
"sync"
)
// MutexKV is a simple key/value store for arbitrary mutexes. It can be used to
// serialize changes across arbitrary collaborators that share knowledge of the
// keys they must serialize on.
//
// The initial use case is to let aws_security_group_rule resources serialize
// their access to individual security groups based on SG ID.
type MutexKV struct {
lock sync.Mutex
store map[string]*sync.Mutex
}
// Locks the mutex for the given key. Caller is responsible for calling Unlock
// for the same key.
func (m *MutexKV) Lock(key string) {
log.Printf("[DEBUG] Locking %q", key)
m.get(key).Lock()
log.Printf("[DEBUG] Locked %q", key)
}
// Unlock the mutex for the given key. Caller must have called Lock for the same key first.
func (m *MutexKV) Unlock(key string) {
log.Printf("[DEBUG] Unlocking %q", key)
m.get(key).Unlock()
log.Printf("[DEBUG] Unlocked %q", key)
}
// Returns a mutex for the given key, no guarantee of its lock status.
func (m *MutexKV) get(key string) *sync.Mutex {
m.lock.Lock()
defer m.lock.Unlock()
mutex, ok := m.store[key]
if !ok {
mutex = &sync.Mutex{}
m.store[key] = mutex
}
return mutex
}
// Returns a properly initialized MutexKV.
func NewMutexKV() *MutexKV {
return &MutexKV{
store: make(map[string]*sync.Mutex),
}
}
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