  In this paper, we report our multiwavelength observations of the
large-amplitude longitudinal oscillations of a filament on 2015 May 3. Located
next to active region 12335, the sigmoidal filament was observed by the
ground-based H$\alpha$ telescopes from GONG and by AIA aboard SDO. The filament
oscillations were most probably triggered by the magnetic reconnection in the
filament channel. The directions of oscillations have angles of
4$^\circ$-36$^\circ$ with respect to the filament axis. The whole filament did
not oscillate in phase as a rigid body. Meanwhile, the periods (3100$-$4400 s)
of oscillations have a spatial dependence. The values of $R$ are estimated to
be 69.4$-$133.9 Mm, and the minimum transverse magnetic field of the dips is
estimated to be 15 G. The amplitudes of S5-S8 grew with time, while the
amplitudes of S9-S14 damped with time. The amplitudes of oscillations range
from a few to ten Mm, and the maximal velocity can reach 30 km s$^{-1}$.
Interestingly, the filament experienced mass drainage southwards at a speed of
$\sim$27 km s$^{-1}$. The oscillations continued after the mass drainage and
lasted for more than 11 hr. After the mass drainage, the phases of oscillations
did not change a lot. The periods of S5-S8 decreased, while the periods of
S9-S14 increased. The amplitudes of S5$-$S8 damped with time, while the
amplitudes of S9-S14 grew. Most of the damping (growing) ratios are between -9
and 14. We propose a schematic cartoon to explain the complex behaviors of
oscillations by introducing thread-thread interaction.
