英文:
Is it a good practice to lock some data outside if-else and unlock inside if-else
问题
当我测试rf.state == candidate时，可能会出现竞争条件。所以在此之前，我会锁定结构体rf。我想确保rf.state在if条件测试中出现的时候，我可以使用它的最新值。
有没有其他习惯用法来在类似情况下锁定数据（if-else、switch...）？
编辑：
这是我其他一些代码。
...
rf.mu.Lock()
switch rf.state {
case follower:
rf.mu.Unlock()
select {
case <-rf.chanAppends:
case <-rf.chanGrantVotes:
case <-time.After(time.Duration(500+rand.Intn(1000)) * time.Millisecond):
rf.mu.Lock()
rf.state = candidate
rf.mu.Unlock()
}
case candidate:
rf.mu.Unlock()
...
case leader:
rf.mu.Unlock()
...
}
为了在switch中使用当前的rf.state，我必须在外部进行锁定，并在内部进行解锁。让我困扰的是，对于每个case，我都必须解锁（使代码变得不够清晰和可读？）。而且在每个case中都有一些阻塞操作（例如time.After(...)），所以我看不到使用defer来帮助我的方法。我想这是一种权衡，如果我不想改变这个switch的逻辑结构的话。
英文:
When I test rf.state == candidate, there could be a race. So I lock the struct rf before that. I want to make sure rf.state appears exactly in the if condition test so I can use its most current value.
...
func (rf *Raft) runElection() {
rf.mu.Lock()
rf.currentTerm += 1
rf.votedFor = rf.me
rf.votes = 1
rf.mu.Unlock()
for server := range rf.peers {
rf.mu.Lock()
if server != rf.me && rf.state == candidate {
rf.mu.Unlock()
go rf.sendRequestVote(server)
} else {
rf.mu.Unlock()
}
}
}
...
Is there any other idiomatic way to lock the data in similar situations (if-else, switch...)?
EDITS:
Here is some other code of mine.
...
rf.mu.Lock()
switch rf.state {
case follower:
rf.mu.Unlock()
select {
case <-rf.chanAppends:
case <-rf.chanGrantVotes:
case <-time.After(time.Duration(500+rand.Intn(1000)) * time.Millisecond):
rf.mu.Lock()
rf.state = candidate
rf.mu.Unlock()
}
case candidate:
rf.mu.Unlock()
...
case leader:
rf.mu.Unlock()
...
To use the current rf.state upon switch, I have to lock at the outside and unlock it at the inside. What bothers me is that for every case I have to unlock for every cases (making the code less clean and readable?). And there is some blocking (e.g. time.After(...)) going on to make a timer inside every case so I see no way of using defer to help me. I guess it's some tradeoff I have to make if I don't want to alter the logical structure of this switch?
答案1
得分: 1
你的代码看起来还不错，但是你可以将其中的部分提取到自己的函数中，以便使用defer。
func (rf *Raft) runElection() {
// ...
for server := range rf.peers {
tryVote(rf, server)
}
}
func tryVote(rf *Raft, server xxx) {
rf.mu.Lock()
defer rf.mu.Unlock()
if server != rf.me && rf.state == candidate {
go rf.sendRequestVote(server)
}
}
当你的代码变得更加复杂，并且你想要确保互斥锁在从某个代码段返回后绝对被解锁时，这种方法尤其有用。
英文:
While your code looks okay, you can always extract parts into their own functions to make use of defer.
func (rf *Raft) runElection() {
// ...
for server := range rf.peers {
tryVote(rf, server)
}
}
func tryVote(rf *Raft, server xxx) {
rf.mu.Lock()
defer rf.mu.Unlock()
if server != rf.me && rf.state == candidate {
go rf.sendRequestVote(server)
}
}
This is especially helpful when your code gets more complex and you want to make ABSOLUTELY sure the mutex gets unlocked once you return from some code section.
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