Map concurrency and read-write problem in Golang and its solving method

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

One,map concurrency and read-write problems

Fatal error:concurrent map Read and map write error if map is read and written simultaneously by multiple co-processes

The following code is easy to appear map concurrency Read and write problems

Func Main () {

c: = Make (Map[string]int)
Go func () {//Open a co-process to writeMap
For j: = 0; J < 1000000; J + + {
C[fmt. Sprintf ("%d", j)] = J
}
}()
Go func () {//Open a co-process readMap
For j: = 0; J < 1000000; J + + {
Fmt. Println (c[fmt. Sprintf ("%d", j)])
}
}()

Time. Sleep (time. SECOND*20)

}

Fatal Error:concurrent Map writes errors occur with multiple concurrent writes

The following code is prone to the problem of map concurrency write

Func Main () {

c: = Make (Map[string]int)

For I: = 0; I < 100; i++ {
Go func () {//Open -concurrent write of a processMap
For j: = 0; J < 1000000; J + + {
C[fmt. Sprintf ("%d", j)] = J
}
}()
}
Time. Sleep (time. SECOND*20)//Let the executionMainmain co-forming wait for function20s,Otherwise, the above concurrency operation will not be performed

}

Second, the cause of the problem

Because map is a reference type, even if a function is called, the parameter copy still points to the mapping m, so multiple goroutine concurrently write the same mapping m , the students who write too many threads know that, for shared variables, resources, concurrent read and write will produce competition, so the sharing of resources is compromised

Third, the solution

1, lock

(1) Universal Lock

Type Demo struct {

Data map[string]string

Lock sync. Mutex

}

Func (d Demo) Get (k string) string{

D.lock.lock ()

Defer D.lock.unlock ()

return D.data[k]

}

Func (d Demo) Set (K,v string) {

D.lock.lock ()

Defer D.lock.unlock ()

D.data[k]=v

}

(2) read/write lock

Type Demo struct {

Data map[string]string

Lock sync. Rwmutex

}

Func (d Demo) Get (k string) string{

D.lock.rlock ()

Defer D.lock.runlock ()

return D.data[k]

}

Func (d Demo) Set (K,v string) {

D.lock.lock ()

Defer D.lock.unlock ()

D.data[k]=v

}

2, the use of channel serialization processing