Golang in Rwmutex-related

This is a creation in Article, where the information may have evolved or changed.

About sync. Rwmutex

About the priority level

• In order to emulate barrier in Pthread, the Rwmutex mate blocking pipeline is used in the code. One of the key issues is the priority of read and write locks.
• In the document there is this sentence: a blocked lock call excludes new readers from acquiring the lock.
  So we can see that a blocked write lock prevents the new reader from requesting a read lock.
• To summarize, we can put the program in stages to illustrate this behavior.
  • N readers add n read locks
  • A writer tries to add a write lock that is blocked
  • Subsequent readers cannot successfully acquire a read lock.
  • Unlock all n Read locks
  • Write lock is awakened, write operation is completed, write lock is unlocked
  • Subsequent readers are awakened, read locks are received, and read operations are completed
• Test code:

package mainimport "fmt"import "time"import "sync"func main() {    var wg sync.WaitGroup    var rw sync.RWMutex    wg.Add(3)    go func() {        defer wg.Done()        rw.RLock()        time.Sleep(3 * time.Second)        rw.RUnlock()    }()    go func() {        defer wg.Done()        time.Sleep(1 * time.Second)        rw.Lock()        fmt.Println("Get Write Lock")        rw.Unlock()    }()    go func() {        defer wg.Done()        time.Sleep(2 * time.Second)        rw.RLock()        fmt.Println("Get Read Lock")        rw.RUnlock()    }()    wg.Wait()}输出: Get Write Lock     Get Read Lock

Wake-up problem for locks

• What happens when the lock is lifted. Continue to execute goroutine or wake up waiting locks?
• Test code:

package mainimport "fmt"import "time"import "sync"func main() {    var wg sync.WaitGroup    var fuck sync.RWMutex    wg.Add(2)    go func() {        time.Sleep(20 * time.Millisecond)        for i := 0; i < 1000; i++ {            fuck.Lock()            fmt.Printf("Write lock %d\n",i)            fuck.Unlock()        }        wg.Done()    }()    go func() {        time.Sleep(18 * time.Millisecond)        for i := 0; i < 1000; i++ {            fuck.RLock()            fmt.Printf("Read lock %d\n",i)            fuck.RUnlock()        }        wg.Done()    }()    wg.Wait()}输出:    N * Read lock    Write lock    Read lock    Write lock    Read lock    Write lock    Read lock    ....    N * Write lock

• Conclusion after unlocking, go will wake up the waiting lock instead of continuing to execute
• It seems that sleep will be awakened (to be solved)