The difference between sync.Mutex and sync.RWMutex

In the Go language, sync.Mutex and sync.RWMutex are both mutexes used to synchronize access to shared resources in concurrent programming, but their usage scenarios and working principles differ.

The specific differences are as follows:

1. sync.Mutex (Mutex)#

sync.Mutex is the most basic locking mechanism, ensuring that only one goroutine can access the shared resource at any given time.

Characteristics:

Exclusive lock: At any given time, only one goroutine can acquire the lock, while other goroutines must wait for the lock to be released.
Locking and unlocking: Call Lock() to acquire the lock, and call Unlock() to release it.

Applicable scenario: Use sync.Mutex when resource access is relatively simple and there are no cases of many reads and few writes.

Example:

var mu sync.Mutex
mu.Lock()
// Access shared resource
mu.Unlock()

2. sync.RWMutex (Read-Write Mutex)#

sync.RWMutex is a more flexible lock that allows multiple goroutines to read shared resources concurrently, but will block all other read and write operations during write operations.

Characteristics:

Read lock: Multiple goroutines can simultaneously acquire the read lock and read shared resources in parallel.
Write lock: The write lock is exclusive; during the period the write lock is held, no other read or write operations can occur.
Locking and unlocking: Call RLock() to acquire the read lock, call Lock() to acquire the write lock; RUnlock() releases the read lock, and Unlock() releases the write lock.

Applicable scenario: Suitable for scenarios with many reads and few writes, as concurrent read locks can improve performance, but write operations will still experience some blocking.

Example:

var rwMutex sync.RWMutex

// Read operation
rwMutex.RLock()
// Read shared resource
rwMutex.RUnlock()

// Write operation
rwMutex.Lock()
// Write to shared resource
rwMutex.Unlock()

Summary:#

sync.Mutex: Suitable for all read-write scenarios, but can cause performance bottlenecks in concurrent read operations.
sync.RWMutex: Suitable for scenarios with many reads and few writes, can improve performance for concurrent reads, but write operations remain exclusive.

If your application has a large number of read operations and few write operations, using sync.RWMutex can improve performance; otherwise, sync.Mutex is simple and straightforward.