The problem that we keep encountering is that randomly the threads hang or never return.

For a thread to be joinable, it must "return" from it's code block with a return statement, OR reach the end of the code block.

Since you didn't show how you wrote &somefunction, I can only generalize.

sub somefunction{

# somehow incorporate an alarm or a loop
# to run a "return" or "goto END" 
.......
if ( $shared_flag ==1 ){ return }
#or
if( $shared_flag == 1 ){ goto END }
......
......

END:
}
[download]

or maybe alarm?

sub somefunction{
  local $SIG{ALRM} = sub { goto END };
  alarm 10; # wait 10 seconds before interrupting 

  while (1){sleep}

END:
}
[download]

You can also try to detach the thread, and have it set a shared variable when it successfully completes. Then loop through the shared flags at the end of your main thread, and kill hanging threads.