CRYPTO_r_lock.CRYPTO_r_lock

Undocumented in source but is binding to C. You might be able to learn more by searching the web for its name.
template CRYPTO_r_lock(string type)
version(!CRYPTO_w_lock)
extern (C) nothrow @nogc
enum CRYPTO_r_lock = "libressl_d.openssl.crypto.CRYPTO_lock(libressl_d.openssl.crypto.CRYPTO_LOCK | libressl_d.openssl.crypto.CRYPTO_READ, " ~ type ~ ", __FILE__, __LINE__);";

Meta