core: making block_registry thread-safe for multiple flowgraphs to access it.
Merge branch 'maint'
runtime: (dup of e0f9a39 for 3.7 structure) making block_registry thread-safe for multiple flowgraphs to access it.
runtime: 2 threading issues with the shared memory system.

1. Making a global mutex for the VM circular buffers to use and lock for multiple top_blocks to handle accessing the memory.

2. Catch the bad_alloc exception once and retry. After 1., this rarely happens unless the thread count gets large (> 20 as an estimate).
grc: fix usage of file descriptor source/sink
analog: fixed agc3_cc_impl GCC assumption
runtime: 2 threading issues with the shared memory system.

1. Making a global mutex for the VM circular buffers to use and lock for multiple top_blocks to handle accessing the memory.

2. Catch the bad_alloc exception once and retry. After 1., this rarely happens unless the thread count gets large (> 20 as an estimate).
Merge branch 'maint'
Merge branch 'master_vmcircbuf_mutex'
Merge branch 'master' of git.gnuradio.org:gnuradio
runtime: removing mutex locks; broke other things more important than what it fixed.
runtime: ignore last commit. Problem was an extra lock inside the test routine that shouldn't have been there.
Merge remote-tracking branch 'ncorgan/agc3_cc_impl_fix'
analog: fixup whitespace in agc3_cc_impl.cc