从文件读取而不锁定文件

Question

I constantly write to one file some data everytime requests come in. I also want to parse this file and read from it sometimes. How can I do this reading if the file is constantly being written to? What's the pattern?

Answer 1

You could make use of sync.RWMutex. Then:

• When you need to read the file, call RLock(), read, then call RUnlock().
• When you need to write to the file, call Lock(), write, then call Unlock().

As long as you do that, you're ensuring that:

• Only one goroutine will be writing to the file at any time.
• If you try to read the file while it's being modified, the lock will wait until you finish writing before starting to read the file.
• If you try to write to the file while it's being read, the lock will wait until you finish reading before starting to write.

Here's a very little example:

package sample

import (
    "sync"
)

var fileMutex = new(sync.RWMutex)

func readFile() {
    fileMutex.RLock()
    defer fileMutex.RUnlock()

    // Read the file. Don't modify it.
}

func writeFile() {
    fileMutex.Lock()
    defer fileMutex.Unlock()

    // Write to the file.
}