Golang中Buffer高效拼接字符串以及自定义线程安全Buffer

news/2024/6/29 2:57:25

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Go中可以使用“+”合并字符串，但是这种合并方式效率非常低，每合并一次，都是创建一个新的字符串,就必须遍历复制一次字符串。Java中提供StringBuilder类(最高效,线程不安全)来解决这个问题。Go中也有类似的机制，那就是Buffer(线程不安全)。

以下是示例代码：

package mainimport ("bytes""fmt"
)func main() {var buffer bytes.Bufferfor i := 0; i < 1000; i++ {buffer.WriteString("a")}fmt.Println(buffer.String())
}

使用bytes.Buffer来组装字符串，不需要复制，只需要将添加的字符串放在缓存末尾即可。

Buffer为什么线程不安全?

The Go documentation follows a simple rule: If it is not explicitly stated that concurrent access to something is safe, it is not.

==Go文档遵循一个简单的规则：如果没有明确声明并发访问某事物是安全的，则不是。==

以下是Golang中bytes.Buffer部分源码

// A Buffer is a variable-sized buffer of bytes with Read and Write methods.
// The zero value for Buffer is an empty buffer ready to use.
type Buffer struct {buf       []byte   // contents are the bytes buf[off : len(buf)]off       int      // read at &buf[off], write at &buf[len(buf)]bootstrap [64]byte // memory to hold first slice; helps small buffers avoid allocation.lastRead  readOp   // last read operation, so that Unread* can work correctly.
}// Write appends the contents of p to the buffer, growing the buffer as
// needed. The return value n is the length of p; err is always nil. If the
// buffer becomes too large, Write will panic with ErrTooLarge.
func (b *Buffer) Write(p []byte) (n int, err error) {b.lastRead = opInvalidm := b.grow(len(p))return copy(b.buf[m:], p), nil
}// Read reads the next len(p) bytes from the buffer or until the buffer
// is drained. The return value n is the number of bytes read. If the
// buffer has no data to return, err is io.EOF (unless len(p) is zero);
// otherwise it is nil.
func (b *Buffer) Read(p []byte) (n int, err error) {b.lastRead = opInvalidif b.off >= len(b.buf) {// Buffer is empty, reset to recover space.b.Truncate(0)if len(p) == 0 {return}return 0, io.EOF}n = copy(p, b.buf[b.off:])b.off += nif n > 0 {b.lastRead = opRead}return
}

源码对于Buffer的定义中,并没有关于锁的字段,在write和read函数中也未发现锁的踪影,所以符合上面提到的文档中的rule,即Buffer并发是不安全的。

如何自定义实现一个并发安全的Buffer

type Buffer struct {b bytes.Bufferrw sync.RWMutex
}
func (b *Buffer) Read(p []byte) (n int, err error) {b.rw.RLock()defer b.rw.RUnlock()return b.b.Read(p)
}
func (b *Buffer) Write(p []byte) (n int, err error) {b.rw.Lock()defer b.rw.Unlock()return b.b.Write(p)
}

通过读写锁,解决并发读写问题,以上提供了Read和Write函数,亲,是不是Golang代码简洁明了?其它函数可以在Golang关于Buffer源码的基础上自行实现

两种锁的区别

sync.Mutex(互斥锁)	sync.RWMutex(读写锁)
当一个goroutine访问的时候，其他goroutine都不能访问，保证了资源的同步，避免了竞争，不过也降低了性能	非写状态时:多个Goroutine可以同时读,一个Goroutine写的时候,其它Goroutine不能读也不能写,性能好