[mythtv] Mythtv pes_malloc and pes_free

Roger James roger at beardandsandals.co.uk
Sun May 7 10:53:38 UTC 2017

The libmythtv implementation of mpeg2 uses its own simple heap management 
overlayed on top of the standard heap allocator (malloc/free). This is 
implemented by two functions in pespacket.cpp, pes_alloc and pes_free. The 
reason for doing this is given in the code as "avoiding the global malloc 
lock". The global malloc lock has not existed in glibc malloc for a number 
of years now. Glibc malloc is based on pthreads malloc a.k.a. ptmalloc2. 
This is a multithreading friendly allocator using a sophisticated multi 
arena allocation algorithm.

The simple algorithm in pes_alloc does not play well in a mixed short/long 
term allocation environment causing large amounts of virtual memory space 
to used unnecessarily.

I would like to propose that we consider reverting to the default heap 
allocator. There are also a number of alternatives to the ptmalloc 
allocator that could be consider, for example tcmalloc from Google.

The topic is open to debate!


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