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Join

Category: Async · Status: stub · Lessons: chapter 01, Threads

One line: Waiting for a thread or task to finish, usually receiving its result or its failure through a handle.

Also called: join handle, JoinHandle, WaitGroup, await.

How it connects

flowchart LR
  n_fork_join["Fork-join"]
  n_join["Join"]
  n_structured_concurrency["Structured concurrency"]
  n_fork_join -->|uses| n_join
  n_structured_concurrency -->|uses| n_join
  classDef center stroke-width:3px
  class n_join center
  classDef outside stroke-dasharray: 4 3
  class n_fork_join,n_structured_concurrency outside

In each language
Rust JoinHandle::join ↗ returns the thread's result, or Err if the thread panicked
Go no handle to join: count goroutines with a sync.WaitGroup ↗, which also has a Go method, or receive their results on a channel
C pthread_join ↗ suspends the caller until the target thread terminates
C++ std::thread::join ↗; destroying a thread that is still joinable calls std::terminate (destructor ↗), which a std::jthread ↗ avoids by joining
Java Thread.join ↗, or get on a Future ↗
Python Thread.join ↗
C# Thread.Join ↗; for tasks, await or Task.WhenAll ↗
JavaScript Promise.all ↗, which rejects as soon as any input promise rejects
Kotlin Job.join ↗ suspends until the job is complete, for any reason
Swift await a task's value (Swift book ↗)
Erlang and Elixir Task.await ↗
The operating system waitpid ↗ for a child process

Where to read more