When developing concurrent systems, a common issue that programmers encounter is starvation. Starvation occurs when a concurrency control scheme designed to handle concurrent access to shared resources ends up excessively delaying or even completely denying service to some requests. In this article, we will explore how you can avoid starvation problems when writing concurrent programs in the Go programming language.
Understanding Starvation
Starvation in concurrent programming arises when certain processes or threads are perpetually denied the resources they require to proceed. Typical scenarios include a thread that waits indefinitely due to higher priority threads consuming the available computing resources.
Identifying Starvation in Go
In Go, starvation can occur in various constructs like goroutines, channels, and for loops. Consider the example:
package main
import (
"fmt"
"time"
)
func worker(id int, jobs <-chan int, results chan<- int) {
for j := range jobs {
fmt.Println("Worker", id, "started job", j)
time.Sleep(time.Second)
fmt.Println("Worker", id, "finished job", j)
results <- j * 2
}
}
func main() {
const numJobs = 5
jobs := make(chan int, numJobs)
results := make(chan int, numJobs)
for w := 1; w <= 3; w++ {
go worker(w, jobs, results)
}
for j := 1; j <= numJobs; j++ {
jobs <- j
}
close(jobs)
for r := 1; r <= numJobs; r++ {
<-results
}
}In this implementation, workers are created to process jobs. If a balance isn't maintained between the generation and processing of jobs, some workers could starve while others are pre-occupied.
Strategies to Avoid Starvation
Let's discuss some techniques to prevent starvation using Go:
Use of Go Scheduler
Rely on Go's powerful runtime scheduler which balances workload efficiently. It's designed to preempt goroutine execution and prevent one from blocking others indefinitely.
Yielding Timeslices
Strategically invoke time functions that can yield processor time thus allowing blocked or waiting goroutines a chance to execute:
package main
import (
"fmt"
"time"
)
func main() {
for i := 1; i <= 10; i++ {
go func(i int) {
time.Sleep(time.Millisecond * 100)
fmt.Println("Job", i)
}(i)
}
time.Sleep(time.Second)
}In the example, sleep calls are deliberately added to allow time for other goroutines to proceed with their tasks across available processors.
Priority Scheduling
Utilize custom scheduling algorithms leveraging channels or semaphores to hand-off priority jobs to available resources:
// Priority can be managed via separate queues (channels) for high and low priority tasks.
// Priority handling with select types on channels. Here’s a sample indicating priority via separate channels.package main
import (
"fmt"
)
func priorityWorker(priorityJobs <-chan int, regularJobs <-chan int) {
for {
select {
case j := <-priorityJobs:
fmt.Println("Processing priority job", j)
case j := <-regularJobs:
fmt.Println("Processing regular job", j)
}
}
}
func main() {
priorityJobs := make(chan int, 5)
regularJobs := make(chan int, 5)
go priorityWorker(priorityJobs, regularJobs)
for i := 1; i <= 5; i++ {
priorityJobs <- i
regularJobs <- i
}
}The use of select in workers allows Go programs to prioritize or pick from multiple operations judiciously.
Conclusion
Managing concurrent operations to avoid starvation requires excellent understanding and well-thought-out designs. Proper utilization of Go's scheduler features, implementing appropriate time phasing, or establishing job priority can prevent such issues effectively.
