CODEWITHSUNDEEP
androidjava-native-interfacedalvikweak-references
pakerfeldt
pakerfeldt

Reputation: 1466

Weak global reference on Android 2.3 not working (JNI)

With JNI, I'm creating a weak global ref from a jobject. And later, when trying to access this reference, the dalvik vm crashes on Android 2.3 but not on 4.1 and 4.2. What I found out was that IsSameObject with the object itself and the created weak reference as parameters returns 1 on the working devices and 0 on the devices where it crashes. Does that make sense? Changing to GlobalRef and IsSameObject returns 1.

Here I'm testing IsSameObject right after creating the weak global reference.

this->jMyObject = getEnv()->NewWeakGlobalRef(jMyObject);
LOGV("Is same object = %d", getEnv()->IsSameObject(jMyObject, this->jMyObject));

LOGV is my macro for printing to logcat.

The crash log isn't very helpful to me:

01-09 09:57:04.778: I/DEBUG(13012): Build fingerprint: 'google/passion/passion:2.3.7/GWK74/121341:user/release-keys'
01-09 09:57:04.778: I/DEBUG(13012): pid: 15001, tid: 15001  >>> org.example.myproject <<<
01-09 09:57:04.778: I/DEBUG(13012): signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr de5d8e6f
01-09 09:57:04.778: I/DEBUG(13012):  r0 0018fed8  r1 00000007  r2 de5d8e6f  r3 00000002
01-09 09:57:04.778: I/DEBUG(13012):  r4 437d45d4  r5 431ecda8  r6 beb54098  r7 000010f8
01-09 09:57:04.778: I/DEBUG(13012):  r8 aca12000  r9 0000000c  10 431ecd94  fp aca9f368
01-09 09:57:04.778: I/DEBUG(13012):  ip 000000f8  sp beb54048  lr aca15e2c  pc aca15e18  cpsr a0000010
01-09 09:57:04.778: I/DEBUG(13012):  d0  0065007200670067  d1  006e006900730000
01-09 09:57:04.778: I/DEBUG(13012):  d2  275449202121213a  d3  4546455220412000
01-09 09:57:04.778: I/DEBUG(13012):  d4  8000000000000000  d5  429800003f800000
01-09 09:57:04.778: I/DEBUG(13012):  d6  00000000c2980000  d7  4110000042500000
01-09 09:57:04.778: I/DEBUG(13012):  d8  0000000043eb0000  d9  c35c0000439ce2e0
01-09 09:57:04.778: I/DEBUG(13012):  d10 433d5140405277a8  d11 0000000042354500
01-09 09:57:04.778: I/DEBUG(13012):  d12 0000000000000000  d13 0000000000000000
01-09 09:57:04.778: I/DEBUG(13012):  d14 0000000000000000  d15 0000000000000000
01-09 09:57:04.778: I/DEBUG(13012):  d16 000000000065dea0  d17 c053000000000000
01-09 09:57:04.778: I/DEBUG(13012):  d18 0000000000000000  d19 0000000000000000
01-09 09:57:04.778: I/DEBUG(13012):  d20 3ff0000000000000  d21 8000000000000000
01-09 09:57:04.778: I/DEBUG(13012):  d22 0000000000000000  d23 0000000000000000
01-09 09:57:04.778: I/DEBUG(13012):  d24 0000000000000000  d25 407c000000000000
01-09 09:57:04.778: I/DEBUG(13012):  d26 4030000000000000  d27 3ff0000000000000
01-09 09:57:04.778: I/DEBUG(13012):  d28 0100010001000100  d29 3ff0000000000000
01-09 09:57:04.778: I/DEBUG(13012):  d30 0000000000000000  d31 3ff0000000000000
01-09 09:57:04.778: I/DEBUG(13012):  scr 20000010
01-09 09:57:04.828: I/DEBUG(13012):          #00  pc 00015e18  /system/lib/libdvm.so
01-09 09:57:04.828: I/DEBUG(13012):          #01  pc 0001c0e4  /system/lib/libdvm.so
01-09 09:57:04.828: I/DEBUG(13012):          #02  pc 0001afdc  /system/lib/libdvm.so
01-09 09:57:04.828: I/DEBUG(13012):          #03  pc 00059c40  /system/lib/libdvm.so
01-09 09:57:04.828: I/DEBUG(13012):          #04  pc 00046666  /system/lib/libdvm.so
01-09 09:57:04.828: I/DEBUG(13012):          #05  pc 001b0d3e  /data/data/org.example/lib/libmyproject.so
01-09 09:57:04.828: I/DEBUG(13012):          #06  pc 001b4c7e  /data/data/org.example/lib/libmyproject.so

Do I need to extract the object from the reference? Or should I just avoid weak references altogether?

Upvotes: 1

Views: 797

Answers (1)

pakerfeldt
pakerfeldt

Reputation: 1466

If I put the weak reference in a NewLocalRef it seems to be doing fine. So I ended up with:

jobject jMyObject = getEnv()->NewLocalRef(jMyWeakObject);
if(!getEnv()->IsSameObject(jMyObject, NULL)) {
    // do stuff with object
}

And the member variable is now jMyWeakObject.

Upvotes: 4

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