Note that even though only two threads are running a call to foo(), the spawn count equals 3. This is because the spawn count includes calls that have already completed. Thus, the 3 corresponds to thread 0's already completed call to foo(0), thread 1's current call to foo(1), and thread 0's current call to foo(2). The descriptor will be able to be freed once the spawn count equals done.
Note that even though only two threads are running a call to foo(), the spawn count equals 3. This is because the spawn count includes calls that have already completed. Thus, the 3 corresponds to thread 0's already completed call to foo(0), thread 1's current call to foo(1), and thread 0's current call to foo(2). The descriptor will be able to be freed once the spawn count equals done.