Learning Concurrency in Kotlin

Deadlocks

Often, in order to guarantee that concurrent code is synchronized correctly, it's necessary to suspend or block execution while a task is completed in a different thread. But due to the complexity of these situations, it isn't uncommon to end up in a situation where the execution of the complete application is halted because of circular dependencies:

lateinit var jobA : Joblateinit var jobB : Jobfun main(args: Array<String>) = runBlocking {    jobA = launch {        delay(1000)        // wait for JobB to finish        jobB.join()     }    jobB = launch {        // wait for JobA to finish        jobA.join()    }    // wait for JobA to finish    jobA.join()    println("Finished")}

Let's take a look at a simple flow diagram of jobA.

Flow chart of jobA

In this example, jobA is waiting ...