Preparser crash

Description

An assertion related to refcount fails from the preparser thread.

Expected behavior

The assertion should pass 😄

Actual behavior

There is some refcount issue causing a segfault from the preparser thread:

07-27 09:14:36.175 19225 20032 F libc    : Fatal signal 6 (SIGABRT), code -6 in tid 20032 (vlc-preparse)
07-27 09:14:36.277   201   201 F DEBUG   : *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
07-27 09:14:36.277   201   201 F DEBUG   : Build fingerprint: 'google/hammerhead/hammerhead:6.0.1/M4B30Z/3437181:user/release-keys'
07-27 09:14:36.277   201   201 F DEBUG   : Revision: '11'
07-27 09:14:36.277   201   201 F DEBUG   : ABI: 'arm'
07-27 09:14:36.277   201   201 F DEBUG   : pid: 19225, tid: 20032, name: vlc-preparse  >>> org.videolan.vlc.debug <<<
07-27 09:14:36.277   201   201 F DEBUG   : signal 6 (SIGABRT), code -6 (SI_TKILL), fault addr --------
07-27 09:14:36.303   201   201 F DEBUG   : Abort message: '../../include/vlc_atomic.h:59: void vlc_atomic_rc_inc(vlc_atomic_rc_t *): assertion "prev" failed'
07-27 09:14:36.304   201   201 F DEBUG   :     r0 00000000  r1 00004e40  r2 00000006  r3 95482978
07-27 09:14:36.304   201   201 F DEBUG   :     r4 95482980  r5 95482930  r6 00000002  r7 0000010c
07-27 09:14:36.304   201   201 F DEBUG   :     r8 88e4f190  r9 95482730  sl 95482568  fp 954825a8
07-27 09:14:36.304   201   201 F DEBUG   :     ip 00000006  sp 954824d8  lr b6c95b61  pc b6c97f50  cpsr 40010010
07-27 09:14:36.321   201   201 F DEBUG   : 
07-27 09:14:36.321   201   201 F DEBUG   : backtrace:
07-27 09:14:36.321   201   201 F DEBUG   :     #00 pc 00041f50  /system/lib/libc.so (tgkill+12)
07-27 09:14:36.321   201   201 F DEBUG   :     #01 pc 0003fb5d  /system/lib/libc.so (pthread_kill+32)
07-27 09:14:36.322   201   201 F DEBUG   :     #02 pc 0001c30f  /system/lib/libc.so (raise+10)
07-27 09:14:36.322   201   201 F DEBUG   :     #03 pc 000194c1  /system/lib/libc.so (__libc_android_abort+34)
07-27 09:14:36.322   201   201 F DEBUG   :     #04 pc 000174ac  /system/lib/libc.so (abort+4)
07-27 09:14:36.322   201   201 F DEBUG   :     #05 pc 0001af23  /system/lib/libc.so (__libc_fatal+16)
07-27 09:14:36.322   201   201 F DEBUG   :     #06 pc 00019549  /system/lib/libc.so (__assert2+20)
07-27 09:14:36.322   201   201 F DEBUG   :     #07 pc 00a7cdb0  /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
07-27 09:14:36.323   201   201 F DEBUG   :     #08 pc 00ab11ec  /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
07-27 09:14:36.323   201   201 F DEBUG   :     #09 pc 00aab504  /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
07-27 09:14:36.323   201   201 F DEBUG   :     #10 pc 00ac6774  /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
07-27 09:14:36.323   201   201 F DEBUG   :     #11 pc 00ac90c8  /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
07-27 09:14:36.323   201   201 F DEBUG   :     #12 pc 00ac9064  /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so (demux_Demux+116)
07-27 09:14:36.323   201   201 F DEBUG   :     #13 pc 00ac1178  /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
07-27 09:14:36.323   201   201 F DEBUG   :     #14 pc 00abe3e4  /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
07-27 09:14:36.323   201   201 F DEBUG   :     #15 pc 00b16714  /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
07-27 09:14:36.323   201   201 F DEBUG   :     #16 pc 0003f45f  /system/lib/libc.so (_ZL15__pthread_startPv+30)
07-27 09:14:36.324   201   201 F DEBUG   :     #17 pc 00019b43  /system/lib/libc.so (__start_thread+6)
07-27 09:14:36.984   201   201 F DEBUG   : 
07-27 09:14:36.984   201   201 F DEBUG   : Tombstone written to: /data/tombstones/tombstone_01

For some reason, ndk-stack could not resolve the symbols:

#02 0x0001c30f /system/lib/libc.so (raise+10)
#03 0x000194c1 /system/lib/libc.so (__libc_android_abort+34)
#04 0x000174ac /system/lib/libc.so (abort+4)
#05 0x0001af23 /system/lib/libc.so (__libc_fatal+16)
#06 0x00019549 /system/lib/libc.so (__assert2+20)
#07 0x00a7cdb0 /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
#08 0x00ab11ec /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
#09 0x00aab504 /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
#10 0x00ac6774 /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
#11 0x00ac90c8 /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
#12 0x00ac9064 /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so (demux_Demux+116)
#13 0x00ac1178 /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
#14 0x00abe3e4 /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
#15 0x00b16714 /data/app/org.videolan.vlc.debug-1/lib/arm/libvlc.so
#16 0x0003f45f /system/lib/libc.so (_ZL15__pthread_startPv+30)
#17 0x00019b43 /system/lib/libc.so (__start_thread+6)
Crash dump is completed

Steps to reproduce

I can reproduce 100%:

Settings > Advanced > Clear media database
Wait a bit
💥

Context

App version

vlc4: current master 4cca6109e2a003c5e7260a9d760b2feee22ed036
vlc-android: current master 94a9ea07
medialibrary: 7c0193d8ad605f91d9721fb9138ef7d57c57903f

Android version

Android 6.0.1, but probably any

Device model

Nexus 5 (a test device)

App mode

Smartphone