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|
package transaction
import (
"context"
"sync"
)
// Repository represents the identity and location of a repository as requested
// by the client
type Repository struct {
ProjectHash string
StorageLoc string // storage location
}
// State represents the current state of a backend node
// Note: in the future this may be extended to include refs
type State struct {
Checksum []byte
}
type RPC struct {
// @zj how do we abstract an RPC invocation? 🤔
}
type Node interface {
Storage() string // storage location the node hosts
ForwardRPC(ctx context.Context, rpc *RPC) error
CheckSum(context.Context, Repository) ([]byte, error)
WriteRef(ctx context.Context, ref, value string) error
}
// MutateTx represents the resources available during a mutator transaction
type MutateTx interface {
AccessTx
// LockRef acquires a write lock on a reference
LockRef(context.Context, string) error
Primary() Node
}
// AccessTx represents the resources available during an accessor transaction
type AccessTx interface {
// Replicas returns all replicas without distinguishing the primary
Replicas() map[string]Node
// RLockRef acquires a read lock on a reference
RLockRef(context.Context, string) error
}
type transaction struct {
shard *Shard
replicas map[string]Node // only nodes verified to be consistent
// unlocks contains callbacks to unlock all locks acquired
unlocks struct {
*sync.RWMutex
m map[string]func()
}
// refRollbacks contains all reference values before modification
refRollbacks map[string][]byte
}
func newTransaction(shard *Shard, good []Node) transaction {
replicas := map[string]Node{}
for _, node := range good {
replicas[node.Storage()] = node
}
return transaction{
shard: shard,
replicas: replicas,
unlocks: struct {
*sync.RWMutex
m map[string]func()
}{
RWMutex: new(sync.RWMutex),
m: make(map[string]func()),
},
}
}
// LockRef attempts to acquire a write lock on the reference name provided.
// If the context is cancelled first, the lock acquisition will be
// aborted.
func (t transaction) LockRef(ctx context.Context, ref string) error {
lockQ := make(chan *sync.RWMutex)
go func() {
t.shard.refLocks.RLock()
l, ok := t.shard.refLocks.m[ref]
t.shard.refLocks.RUnlock()
if !ok {
l = new(sync.RWMutex)
t.shard.refLocks.Lock()
t.shard.refLocks.m[ref] = l
t.shard.refLocks.Unlock()
}
l.Lock()
lockQ <- l
}()
// ensure lockQ is consumed in all code paths so that goroutine doesn't
// stray
select {
case <-ctx.Done():
l := <-lockQ
l.Unlock()
return ctx.Err()
case l := <-lockQ:
t.unlocks.Lock()
t.unlocks.m[ref] = func() { l.Unlock() }
t.unlocks.Unlock()
return nil
}
}
// unlockAll will unlock all acquired locks at the end of a transaction
func (t transaction) unlockAll() {
// unlock all refs
t.unlocks.RLock()
for _, unlock := range t.unlocks.m {
unlock()
}
t.unlocks.RUnlock()
}
func (t transaction) rollback(ctx context.Context) error {
// for ref, value := range t.refRollbacks {
//
// }
return nil
}
func (t transaction) Replicas() map[string]Node {
return t.replicas
}
func (t transaction) Primary() Node {
return t.replicas[t.shard.primary]
}
// RLockRef attempts to acquire a read lock on the reference name provided
// (ref). If the context is cancelled first, the lock acquisition will be
// aborted.
func (t transaction) RLockRef(ctx context.Context, ref string) error {
lockQ := make(chan *sync.RWMutex)
go func() {
t.shard.refLocks.RLock()
l, ok := t.shard.refLocks.m[ref]
t.shard.refLocks.RUnlock()
if !ok {
l = new(sync.RWMutex)
t.shard.refLocks.Lock()
t.shard.refLocks.m[ref] = l
t.shard.refLocks.Unlock()
}
l.RLock()
lockQ <- l
}()
// ensure lockQ is consumed in all code paths so that goroutine doesn't
// stray
select {
case <-ctx.Done():
// unlock before aborting
l := <-lockQ
l.RUnlock()
return ctx.Err()
case l := <-lockQ:
t.unlocks.Lock()
t.unlocks.m[ref] = func() { l.RUnlock() }
t.unlocks.Unlock()
return nil
}
}
|
