This is part of the Semicolon&Sons Code Diary - consisting of lessons learned on the job. You're in the concurrency category.
Last Updated: 2024-04-25
My first naive approach was this
t = Thread.new { sleep(10); "c" }
#<Thread:0x00007fb88849f488@(pry):1 sleep>
res = t.join
#<Thread:0x00007fb88849f488@(pry):1 dead>
Unfortunately this just returned the thread object, now dead.
A similar lack of return values to join exists in another languages, e.g. Python.
Anyway, the simplest general way to get a thread to return values is to store thread-local variables and then access these after calling join
t = Thread.new { sleep(10); Thread.current[:output] = "c" }
t.join
t[:output]
There is also a Ruby specific tool, value
t = Thread.new { sleep(10); "c" }
# This halts execution until the thread is done
t.value
=> "c"