In this paper, we report our multiwavelength observations of the large-amplitude longitudinal oscillations of a filament observed. on 2015 May 3. Located next to active region 12335, the sigmoidal filament was observed by the ground-based H alpha telescopes from the Global Oscillation Network Group and by the Atmospheric Imaging Assembly instrument on. board the Solar Dynamics Observatory. The filament oscillations were most probably triggered by the magnetic reconnection in the filament channel, which is characterized by the bidirectional flows, brightenings in EUV and soft X-ray, and magnetic cancellation in the photosphere. The directions of oscillations have angles of 4 degrees-36 degrees with respect to the filament axis. The whole filament did not oscillate in phase as a rigid body. Meanwhile, the oscillation. periods (3100-4400 s). have a spatial dependence, implying that the curvature radii (R) of the magnetic dips are different at different positions. The values of R are estimated to be 69.4-133.9 Mm, and the minimum transverse magnetic field of the dips is estimated to be 15 G. The amplitudes of S5-S8 grew with time, while the amplitudes of S9-S14 damped with time. The oscillation. amplitudes. range from a few to ten Mm, and the maximum. velocity can reach 30 km s(-1). Interestingly, the filament experienced mass drainage southward. at a speed of similar to 27 km s(-1). The oscillations continued after the mass drainage and lasted for more than 11 hr. After the mass drainage, the oscillation. phases. did not change much. The periods of S5-S8 decreased, while the periods of S9-S14 increased. The amplitudes of S5-S8 damped with time, while the amplitudes of S9-S14 grew. Most of the damping (growing) ratios are between -9 and 14. We offer. a schematic cartoon to explain the complex behaviors of oscillations by introducing thread-thread interaction.