97 lines
2.5 KiB
Go
97 lines
2.5 KiB
Go
|
package multimutex
|
||
|
|
|
||
|
|
import (
|
||
|
|
"fmt"
|
||
|
|
"sync"
|
||
|
|
)
|
||
|
|
|
||
|
|
// cntMutex is a struct that wraps a counter and a mutex, and is used
|
||
|
|
// to keep track of the number of goroutines waiting for access to the
|
||
|
|
// mutex, such that we can forget about it when the counter is zero.
|
||
|
|
type cntMutex struct {
|
||
|
|
cnt int
|
||
|
|
sync.Mutex
|
||
|
|
}
|
||
|
|
|
||
|
|
// Mutex is a struct that keeps track of a set of mutexes with
|
||
|
|
// a given ID. It can be used for making sure only one goroutine
|
||
|
|
// gets given the mutex per ID.
|
||
|
|
type Mutex struct {
|
||
|
|
// mutexes is a map of IDs to a cntMutex. The cntMutex for
|
||
|
|
// a given ID will hold the mutex to be used by all
|
||
|
|
// callers requesting access for the ID, in addition to
|
||
|
|
// the count of callers.
|
||
|
|
mutexes map[uint64]*cntMutex
|
||
|
|
|
||
|
|
// mapMtx is used to give synchronize concurrent access
|
||
|
|
// to the mutexes map.
|
||
|
|
mapMtx sync.Mutex
|
||
|
|
}
|
||
|
|
|
||
|
|
// NewMutex creates a new Mutex.
|
||
|
|
func NewMutex() *Mutex {
|
||
|
|
return &Mutex{
|
||
|
|
mutexes: make(map[uint64]*cntMutex),
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
// Lock locks the mutex by the given ID. If the mutex is already
|
||
|
|
// locked by this ID, Lock blocks until the mutex is available.
|
||
|
|
func (c *Mutex) Lock(id uint64) {
|
||
|
|
c.mapMtx.Lock()
|
||
|
|
mtx, ok := c.mutexes[id]
|
||
|
|
if ok {
|
||
|
|
// If the mutex already existed in the map, we
|
||
|
|
// increment its counter, to indicate that there
|
||
|
|
// now is one more goroutine waiting for it.
|
||
|
|
mtx.cnt++
|
||
|
|
} else {
|
||
|
|
// If it was not in the map, it means no other
|
||
|
|
// goroutine has locked the mutex for this ID,
|
||
|
|
// and we can create a new mutex with count 1
|
||
|
|
// and add it to the map.
|
||
|
|
mtx = &cntMutex{
|
||
|
|
cnt: 1,
|
||
|
|
}
|
||
|
|
c.mutexes[id] = mtx
|
||
|
|
}
|
||
|
|
c.mapMtx.Unlock()
|
||
|
|
|
||
|
|
// Acquire the mutex for this ID.
|
||
|
|
mtx.Lock()
|
||
|
|
}
|
||
|
|
|
||
|
|
// Unlock unlocks the mutex by the given ID. It is a run-time
|
||
|
|
// error if the mutex is not locked by the ID on entry to Unlock.
|
||
|
|
func (c *Mutex) Unlock(id uint64) {
|
||
|
|
// Since we are done with all the work for this
|
||
|
|
// update, we update the map to reflect that.
|
||
|
|
c.mapMtx.Lock()
|
||
|
|
|
||
|
|
mtx, ok := c.mutexes[id]
|
||
|
|
if !ok {
|
||
|
|
// The mutex not existing in the map means
|
||
|
|
// an unlock for an ID not currently locked
|
||
|
|
// was attempted.
|
||
|
|
panic(fmt.Sprintf("double unlock for id %v",
|
||
|
|
id))
|
||
|
|
}
|
||
|
|
|
||
|
|
// Decrement the counter. If the count goes to
|
||
|
|
// zero, it means this caller was the last one
|
||
|
|
// to wait for the mutex, and we can delete it
|
||
|
|
// from the map. We can do this safely since we
|
||
|
|
// are under the mapMtx, meaning that all other
|
||
|
|
// goroutines waiting for the mutex already
|
||
|
|
// have incremented it, or will create a new
|
||
|
|
// mutex when they get the mapMtx.
|
||
|
|
mtx.cnt--
|
||
|
|
if mtx.cnt == 0 {
|
||
|
|
delete(c.mutexes, id)
|
||
|
|
}
|
||
|
|
c.mapMtx.Unlock()
|
||
|
|
|
||
|
|
// Unlock the mutex for this ID.
|
||
|
|
mtx.Unlock()
|
||
|
|
}
|