sync.Cond Signal

04-sync-package/03-cond-signal/main.go

@@ -0,0 +1,38 @@
+package main
+
+import (
+ "fmt"
+ "sync"
+)
+
+var sharedRsc = make(map[string]interface{})
+
+func main() {
+ var wg sync.WaitGroup
+
+ mu := sync.Mutex{}
+ cond := sync.NewCond(&mu)
+
+ wg.Add(1)
+ go func() {
+ defer wg.Done()
+
+ // suspend goroutine until sharedRsc is populated.
+ cond.L.Lock()
+ for len(sharedRsc) == 0 {
+ // time.Sleep(1 * time.Millisecond)
+ cond.Wait()
+ }
+
+ fmt.Println(sharedRsc["rsc1"])
+ cond.L.Unlock()
+ }()
+
+ cond.L.Lock()
+ // writes changes to sharedRsc
+ sharedRsc["rsc1"] = "foo"
+ cond.Signal()
+ cond.L.Unlock()
+
+ wg.Wait()
+}

README.md

@@ -278,4 +278,25 @@ select {
 
 ## sync.Atomic:
 - `Automic` is used to performed low level automic operations on memory. It is used by other synchonization utilities.
-- It is a `lockless` operation.
+- It is a `lockless` operation.
+
+-----------
+
+## sync.Cond:
+- Condition variable is one of the synchronization mechanism.
+- It is a `lockless` operation.
+- A condition variable is basically a container of Goroutines that are waiting for a certain condition.
+- Condition variables are type:
+```go
+var c *sync.Cond
+```
+- We use constructor method `sync.NewCond()` to create a conditional variable, it takes `sync.Locker` interface as input, which is usually `sync.Mutex`.
+```go
+mu := sync.Mutex{}
+cond := sync.NewCond(&mu)
+```
+- Wait suspends the execution of Goroutine.
+- Signal wakes one Goroutine waiting on `c`.
+- Broadcast wakes all Goroutines waiting on `c`.
+
+-----------