Deadlocks (freezes) on FreeBSD:

OpenCL applications using pocl on FreeBSD must be compiled with 
options CFLAGS+=-pthread or CXXFLAGS+=-pthread, otherwise someone risk
that a library may not initialize the threading on BSD independently, 
even if an ICD loader is used.

See: 
	http://www.freebsd.org/cgi/query-pr.cgi?pr=163512

(Source: http://portablecl.org/docs/html/faq.html?highlight=freebsd)