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Scoped thread

Category: Units of execution · Status: stub · Lessons: chapter 01, Threads

One line: A thread whose life is bounded by a block: the block cannot be left until the thread has been joined, which is what lets the thread borrow the block's own local variables.

Also called: structured thread, thread::scope.

How it connects

flowchart LR
  n_dangling_pointer["Dangling pointer"]
  n_detached_thread["Detached thread"]
  n_task_leak["Leaked tasks"]
  n_scoped_thread["Scoped thread"]
  n_thread["Thread"]
  n_detached_thread ---|vs| n_scoped_thread
  n_scoped_thread -->|is a| n_thread
  n_scoped_thread -->|prevents| n_dangling_pointer
  n_scoped_thread -->|prevents| n_task_leak
  classDef center stroke-width:3px
  class n_scoped_thread center
  classDef outside stroke-dasharray: 4 3
  class n_dangling_pointer,n_detached_thread,n_task_leak,n_thread outside

In each language
Rust thread::scope ↗ joins every thread started inside it before returning, so a scoped thread may borrow the caller's locals and needs no 'static bound
C++ std::jthread ↗ joins in its destructor, which bounds the thread by the enclosing block — but nothing checks what the thread captured
Java JEP 505: Structured Concurrency ↗ scopes a set of tasks to a block that does not exit until all of them have finished
Python ThreadPoolExecutor ↗ used as a context manager waits for its threads at the end of the with block

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