Unexpected end of JSON input

[smacker]

Running parsing of files in more than 1 concurrent processes produces driver failure: unexpected end of JSON input from time to time.
It looks like a race condition because I can't reproduce it stable.

bblfsh/bblfshd:v2.13.0-drivers

[ncordon]

Files that triggered this error in the latest bblfsh logs:

packages/tcpdf/fonts/arialunicid0.php
www/analytics/libs/tcpdf/tcpdf.php
www/analytics/libs/tcpdf/include/tcpdf_font_data.php
packages/tcpdf/fonts/uni2cid_ag15.php
packages/tcpdf/fonts/uni2cid_ac15.php
YahooUserInterfaceContrib/pub/System/YahooUserInterfaceContrib/examples/autocomplete/assets/php/ysearch_flat.php
YahooUserInterfaceContrib/pub/System/YahooUserInterfaceContrib/examples/datatable/assets/php/json_proxy.php
packages/tcpdf/tcpdf.php