Re: [igraph] Multithreading and GraphML

[Tamas Nepusz]

Hi Chris,

Thanks for reporting and fixing that. My only concern is that you  
cannot be sure that igraph_read_graph_graphml is called in the "main"  
thread, so xmlInitParser() may be called from a different thread. I  
don't know if that matters to libxml2 or not, but the webpage states  
that xmlInitParser() must be called from the main thread. Do you have  
any comments on that? If it really matters, then we should maybe add  
an extra igraph_init() function to the library and make sure that  
Python calls it when it loads the igraph module.

--
Tamas


On 2009.08.18., at 22:19, Chris Wj wrote:

> Hi all, this is just a FYI for anyone working with igraph and doing  
> multithreading. I fixed a bug where igraph crashes in multithreaded  
> apps using libxml2 by adding the following line to 'foreign- 
> graphml.c', line 997 in 'igraph_read_graph_graphml' after the  
> variable declarations.
>
> xmlInitParser();
>
> From http://xmlsoft.org/threads.html:
> call xmlInitParser() in the "main" thread before using any of the  
> libxml2 API
>
> While  'igraph_read_graph_graphml' may be called multiple times, I  
> checked the 'xmlInitParser' function to find this source:
> void
> xmlInitParser(void) {
>     if (xmlParserInitialized != 0)
>     return;
>  #ifdef LIBXML_THREAD_ENABLED
>     __xmlGlobalInitMutexLock();
>     if (xmlParserInitialized == 0) {
> ...
>
> Where it a) locks on __xmlGlobalInitMutexLock(); and b) subsequently  
> sets xmlParserInitialized to 1, so calling it multiple times doesn't  
> really hurt (I am fairly sure of this and will report back if  
> otherwise).
>
> This bug manifested itself using the Python library and Python  
> threads, which are pthreads after all.
>
> -Chris
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