Longitudinal polarized $\vec{p}+\vec{p}$ collisions provide a leading-order probe of the gluon spin contributions to the proton spin. The direct-photon production is named the "golden" channel due to its "cleanliness" and sensitivity to the sign of the gluon spin. The PHENIX measurement at the Relativistic Heavy-Ion Collider performed the first published direct-photon double-helicity asymmetry ($A_{LL}$) measurement. Our data indicate the gluon spin has a large probability of aligning with the proton spin. I will show the direct-photon cross sections and $A_{LL}$ measurements at PHENIX.