[Issue 5488] New: Spawned threads hang in a way that suggests allocation or gc issue

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=5488

           Summary: Spawned threads hang in a way that suggests allocation
                    or gc issue
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Mac OS X
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody at puremagic.com
        ReportedBy: adam_conner_sax at yahoo.com


--- Comment #0 from Adam Conner-Sax <adam_conner_sax at yahoo.com> 2011-01-25 20:05:49 PST ---
Created an attachment (id=882)
code to demonstrate the issue described above

The attached program hangs more often than not during the second set of spawns
(using dmd 2.051 on OSX).  The thread functions do nothing but allocate a large
array and then exit.  In one case the array is an Array!double (from
std.container) and in the other it is a built-in double[].  In the second case,
a large enough array will cause the program to hang.  

Sean Kelly has already done some investigating, quoting from his responses:

1) This one is weird, and doesn't appear related to 4307.  One of the threads
(thread A) is in a GC collection and blocked trying to acquire the mutex
protecting the global thread list within thread_resumeAll.  Another thread
(thread B) is also blocked trying to acquire this mutex for other reasons.  My
best guess is that pthread_mutex in OSX is trying to give ownership of the lock
to thread B, and since thread B is suspended it effectively blocks thread A
from acquiring it to resume execution after the GC cycle. 

2) After some testing, it looks like I was right.  I have a fix for this, but
it's far from ideal (though the diff is small): require everything but
thread_resumeAll to acquire two locks in sequence, while thread_resumeAll only
acquires the second.  I'll try to come up with something better.

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