  Understanding the proton spin composition from the quarks and gluons spin
polarization and their motion is important to test various kinds of sum rules
and nonperturbative properties of hadrons. At the Relativistic Heavy Ion
Collider (RHIC), we collide longitudinally polarized proton beams and measure
the double helicity asymmetry $A_{LL}$, which is an important physical quantity
for extracting the polarized parton distribution functions (PDFs) of the
proton. Direct photon, jet and charged pion production are good channels to
probe the gluon spin polarization inside the proton, with the ability to probe
also the sign of the gluon spin. Direct photon production is the theoretically
``cleanest'' channel, with little fragmentation contribution, but limited by
statistics. On the other hand, jet and charged pion production have more
statistics, but include more hard processes and hadronization effects. I will
present the recent measurements of direct photon, jet and charged pion
$A_{LL}$s at PHENIX and show their complementary roles in extracting the gluon
spin.
