This is not a shared library because of this link error:

cc -Wl,-z,relro -Wl,-z,now -Wl,--as-needed -Wl,-shared -Wl,-soname,libthpool.so.0 -o thpool.so.0.0.0 thpool.o
/usr/bin/ld: /usr/lib/x86_64-linux-gnu/libc_nonshared.a(elf-init.oS): relocation R_X86_64_PC32 against undefined hidden symbol `__init_array_start' can not be used when making a shared object
/usr/bin/ld: final link failed: nonrepresentable section on output
collect2: error: ld returned 1 exit status