etcd互斥鎖與ttl

Question

我正在嘗試創建一個簡單的演示golang etcd客戶端程序，該程序使用etcd互斥鎖來創建具有超時的共享鎖。 目標是使互斥鎖在一段時間后過期。

package main

import (
    "context"
    "log"
    "time"

    "go.etcd.io/etcd/clientv3"
    "go.etcd.io/etcd/clientv3/concurrency"
)

var c chan int

func init() {
    c = make(chan int)
}

func main() {
    client, err := clientv3.New(clientv3.Config{
        Endpoints: []string{"http://localhost:2379"},
    })
    if err != nil {
        panic(err)
    }

    watcher := clientv3.NewWatcher(client)
    channel := watcher.Watch(context.Background(), "/foobar", clientv3.WithPrefix())
    go func() {
        for {
            select {
            case change := <-channel:
                for _, ev := range change.Events {
                    log.Printf("etcd change on key; %s, type = %v", string(ev.Kv.Key), ev.Type)
                }
            }
        }
    }()

    go lockFoobar(client, 1)
    go lockFoobar(client, 2)
    <-c
    <-c
}

func lockFoobar(client *clientv3.Client, id int) {
    res, err := client.Grant(context.Background(), 1)
    if err != nil {
        panic(err)
    }

    session, err := concurrency.NewSession(client, concurrency.WithLease(res.ID))
    if err != nil {
        panic(err)
    }

    mux := concurrency.NewMutex(session, "/foobar")

    log.Printf("trying to lock by #%d\n", id)
    ctx, _ := context.WithTimeout(context.Background(), 15*time.Second)
    if err := mux.Lock(ctx); err != nil {
        log.Printf("failed to lock #%d: %v\n", id, err)
        c <- id
        return
    }

    log.Printf("post-lock #%d (lease ID = %x) bullshit\n", id, res.ID)
    time.Sleep(10 * time.Second)
    ttl, _ := client.TimeToLive(context.TODO(), res.ID)
    log.Printf("post-post-lock-#%d-sleep. lease ttl = %v", id, ttl.TTL)
    // mux.Unlock(ctx)
    // log.Printf("post-unlock #%d bullshit\n", id)

    time.Sleep(200 * time.Millisecond)
    c <- id
}

租約的ttl為1秒，而上下文的超時為5秒，因此，應該在上下文過期時刪除該鎖。 但是，無論上下文超時如何，始終僅在失敗的鎖定之后才刪除“鎖定”鎖定。

這是當前輸出：

2018-10-04 18:39:59.413274 I | trying to lock by #2
2018-10-04 18:39:59.414530 I | trying to lock by #1
2018-10-04 18:39:59.414656 I | etcd change on key; /foobar/2a0966398d0677a2, type = PUT
2018-10-04 18:39:59.414684 I | post-lock #2 (lease ID = 2a0966398d0677a2) bullshit
2018-10-04 18:39:59.415617 I | etcd change on key; /foobar/2a0966398d0677a4, type = PUT
2018-10-04 18:40:10.239045 I | post-post-lock-#2-sleep. lease ttl = 1                       <-- lock for #2 has ttl = 1 even after 10s
2018-10-04 18:40:15.238871 I | failed to lock #1: context deadline exceeded                 <-- lock for #1 fails after 15s

如您所見，＃2的鎖即使在15秒后仍然有效。

在另一個終端中運行ETCDCTL_API=3 etcdctl watch --prefix=true /foobar來監視鍵的更改，顯示以下輸出

PUT
/foobar/2a0966398d0677a2

PUT
/foobar/2a0966398d0677a4

DELETE
/foobar/2a0966398d0677a4

DELETE
/foobar/2a0966398d0677a2

這是預期的行為嗎？ 有沒有辦法實現我想要的目標？

PS：現實中的用例是創建一個程序，該程序可以在多個實例中運行，並且不會在崩潰和/或殺死（SIGKILL）時將鎖保留在etcd中。

Answer 1

經過一番搜索，我找到了這種現象的原因。 會話使租約保持活動狀態，直到發生錯誤或取消。

從session.go ：

...
// keep the lease alive until client error or cancelled context
go func() {
    defer close(donec)
    for range keepAlive {
        // eat messages until keep alive channel closes
    }
}()
...

創建互斥體后，Callint session.Orphan()將阻止會話保持活動狀態並達到我的目的。