Problem with LuaJava, Android and Threads

[matthew@...]

I'll lay out the gory details below, but here's a summary of the problem:

I'm creating two threads (in Java) in an Android app. Each thread has  
its own Lua state and each state is running its own copy of the same  
simple script. The script runs a for loop which prints out a log  
message, sleeps and repeats. The sleep is implemented by a simple  
wrapper that calls the C usleep function. Usleep, according to its  
documentation, suspends the thread that invokes it.

I would expect that the log messages from the two threads should be  
intermingled. Instead, I get all the log messages from the first  
thread followed by all the log messages from the second thread. By  
adjusting the thread priorities, I can get all the second thread's  
messages before the first thread. But I cannot get them to intermingle.

A few points to note:

- I am using a severely truncated implementation of LuaJava that I  
have mangled to use Lua 4.0.1
- if I run this experiment with both threads implemented in Java, it  
behaves as I expect
- if I run this experiment with one thread running my Lua script and  
the second thread implmented in Java, it behaves as I expect
- I have verified that the two separate Lua states are, in fact, two  
separate Lua states; i.e. I am not accidentally referring to the same  
state in both threads (see below for how I did this)

Anyway I would appreciate any suggestions, pointing out obvious things  
I've overlooked, pointing out subtle things that I won't be embarassed  
to have overlooked, etc.

Thanks,

Matt



Implementation details.

I verified that the two Lua states were actually different Lua states  
as follows: first, I checked the two Lua states to make sure were they  
were not the same Java object. Then, I tried to rule out any weirdness  
with the C functions by defining three sets of variables (one set  
defined only in thread 1, one set defined only in thread 2, and one  
set defined in both) then I had each state print out all the  
variables, the ones that weren't defined were nil, and the ones that  
were defined printed out their expected values


Here's the Lua script. 'androidlog' is a wrapper around  
__android_log_print from the NDK. 'threadname' is passed in from Java  
and is different for each thread.


       for k = 1,20 do
         sleep(1000)
         androidlog(threadname, 'Greetings from thread ' .. threadname)
       end



Here's an excerpt from the app's main activity where I create and  
start the threads.

       t1 = new LuaThread("loop.lua", getApplicationContext());
       t1.preload("threadname = 't1'");
       t2 = new LuaThread("loop.lua", getApplicationContext());
       t2.preload("threadname = 't2'");

       t1.start();
       t2.start();


LuaThread is a subclass of Thread. The constructor creates a Lua state  
and stores it in an instance variable. The preload function invokes  
doString on the object's Lua state with the passed in parameter. The  
start method kicks off the object's run method as a separate thread.  
Run basically does doFile with the file name passed in to the object's  
constructor.