Subj : Threads and different SpiderMonkey Runtimes
To   : netscape.public.mozilla.jseng
From : Mads Bondo Dydensborg
Date : Wed Sep 21 2005 03:45 pm

Hi

I have a problem with using SpiderMonkey in my multithreaded C++ program.

I want to use one Runtime/Context/Object pr. thread. That is, I have no 
intention of sharing any JS state at all between the different runtimes. 
Was it not for other communication that my threads wish to perform, I 
could happily fork different processes for each javascript environment.

I have compiled SpiderMonkey using JS_THREADSAFE and nspr.

In my application I create a number of threads. Each thread creates 
runtimes, etc, as needed. So, each thread has its own private Runtime. 
However, they crash at many points, most often when creating or 
destroying a context. Only when running with multiple threads does this 
happen.

The code is unfortunately wrapped in a layer of C++ wrappers, so posting 
it here does not really make sense. It works without a hint of problems 
for singlethreaded applications, and valgrind does not report any 
errors. Obviously I am doing something wrong, but I am hard pressed for 
explanations. An important point: it is my understanding that one does 
not need to use the JS_BeginRequest/EndRequest calls, when there are 
different runtimes. Is that correct? There is only ever the same thread 
accessing any runtime, contexts, etc.

I realize it says the garbage collector is global - but JS_GC takes a 
context as an argument, so I have been hoping that there were no state 
changes/conflicts across runtimes. Information on this subject is a bit 
ambigious - the tutorial says one runtime pr. process, the embedders 
guide says that you can have multiple runtimes pr. application.

A note on using SpiderMonkey in multithreaded applications would be 
great, IMHO.

Here is an example gdb stacktrace of a segmentation fault:

#0  0xb74d2951 in pthread_mutex_lock () from 
/lib/tls/i686/cmov/libpthread.so.0
#1  0xb7384522 in PR_Lock () from /usr/lib/libnspr4.so
#2  0xb738a137 in PR_Select () from /usr/lib/libnspr4.so
#3  0xb738a75e in PR_GetCurrentThread () from /usr/lib/libnspr4.so
#4  0xb7eac143 in js_InitContextForLocking (cx=0x80e2790) at jslock.c:877
#5  0xb7e68747 in js_NewContext (rt=0x80dec48, stackChunkSize=8192)
     at jscntxt.c:103
#6  0xb7e58716 in JS_NewContext (rt=0x80dec48, stackChunkSize=8192)
     at jsapi.c:937
#7  0x08058f8b in ContextImpl (this=0x80ddf68, runtime=@0xb712d250,
     stacksize=8192) at jslib_wrappers.cc:70
#8  0x08055edc in Context (this=0xb712d240, runtime=@0xb712d250,
     stacksize=8192) at jslib_wrappers.cc:92
#9  0x08052f06 in worker::run (this=0x80dda90) at ptest.cc:146
#10 0x0806f078 in super_thread::Start_Thread__ (this=0x80dda90)
     at thread_class.cc:117
#11 0x0806ed35 in Static_do_start (MyThis=0x80dda90) at thread_class.cc:32
#12 0xb74d0ca3 in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#13 0xb746ef5a in clone () from /lib/tls/i686/cmov/libc.so.6


Any help most appreciated.

Thanks in advance

Mads

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