Thread join behaviour

[Matt Soucy]

On 04/14/2012 04:56 PM, Alex Rønne Petersen wrote:
> On 14-04-2012 18:04, Russel Winder wrote:
>> I thought the following would terminate gracefully having printed 0..9
>> in some (random) order:
>>
>> #! /usr/bin/env rdmd
>>
>> import std.algorithm ;
>> import std.range ;
>> import std.stdio ;
>> import core.thread ;
>>
>> int main ( immutable string[] args ) {
>> auto threads = map ! ( ( int a ) {
>> void delegate ( ) f ( ) {
>> return delegate ( ) { writeln ( a ) ; } ;
>> }
>> return new Thread ( f ) ;
>> } ) ( iota ( 10 ) ) ;
>> foreach ( t ; threads ) { t.start ( ) ; }
>> foreach ( t ; threads ) { t.join ( ) ; }
>> return 0 ;
>> }
>>
>> However, this does not happen, at least with 2.059 on Linux as per
>> Debian Unstable. Instead I get:
>>
>> 1
>> 2
>> 4
>> 5
>> 8
>> 3
>> 7
>> 6
>> 9
>> 0
>> core.thread.ThreadException at src/core/thread.d(906): Unable to join thread
>> ----------------
>> /tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/initializingWithAMap.d.9532BBED12C814F25F173A9AEAB96D0D(_Dmain+0x83)
>> [0x425edb]
>> /tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/initializingWithAMap.d.9532BBED12C814F25F173A9AEAB96D0D(extern
>> (C) int rt.dmain2..main(int, char**).void runMain()+0x17) [0x429bab]
>> /tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/initializingWithAMap.d.9532BBED12C814F25F173A9AEAB96D0D(extern
>> (C) int rt.dmain2..main(int, char**).void tryExec(scope void
>> delegate())+0x23) [0x42952b]
>> /tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/initializingWithAMap.d.9532BBED12C814F25F173A9AEAB96D0D(extern
>> (C) int rt.dmain2..main(int, char**).void runAll()+0x3d) [0x429bf9]
>> /tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/initializingWithAMap.d.9532BBED12C814F25F173A9AEAB96D0D(extern
>> (C) int rt.dmain2..main(int, char**).void tryExec(scope void
>> delegate())+0x23) [0x42952b]
>> /tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/initializingWithAMap.d.9532BBED12C814F25F173A9AEAB96D0D(main+0xd3)
>> [0x4294c3]
>> /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xfd) [0x7f1ed17f8ead]
>> ----------------
>>
>> I think I must be having a dumb moment as my reaction continues to be
>> WTF.
>>
>
> http://www.kernel.org/doc/man-pages/online/pages/man3/pthread_join.3.html#ERRORS
>
>
> We can rule out these:
>
> EDEADLK: Can't happen with your code.
> EINVAL (second case): No other thread is trying to join.
> ESRCH: Shouldn't happen since druntime registers threads with libpthread.
>
> So, the first case of EINVAL (thread is not a joinable thread) must be
> the cause. I have no clue *why* though...
>
If you merge the two foreach loops into one, doing t.start();t.join(); 
it doesn't have this issue. Also, when I run your code repeatedly the 
number of successful numbers printed changes a lot.
I'm assuming that you're trying to join a thread that already exited...
-Matt