Set Dalvik execution mode in /data/local.prop using Android

Question

I tried to run Dalvik in portable mode by setting /data/local.prop as follows:

dalvik.vm.execution-mode = int:portable

But after I reboot the device (which is a Nexus 7), app_process (hosting zygote) still starts in jit mode.

However, if I run:

adb shell stop
adb shell setprop dalvik.vm.execution-mode int:portable
adb shell start

Then app_process will run in portable mode. Is /data/local.prop deprecated or something is missing here?

Answer 1

You see that one that you set in local.prop is the backing file that is loaded by init process during bootup. Whatever that is read is stored into a shared memory area that every app has access to if it links the property service library.
Do this echo $ANDROID_PROPERTY_WORKSPACE You will see two comma seperated values. First one is Fd to the shared mem and next is size , This is how the sharedmem region is mmaped into your process .
So setting in local.prop will work only if you reboot the device.

Comments

I always use the eng build variant. So I think there should be something else that is missing. Is there any requirement on the file permission of /data/local.prop?

Also, I don't quite believe Dalvik cache will have an effect on this. But for safety I recompiled again with eng build variant, wiped the cache, set the file permission to 750 root:root, rebooted, and it works.

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The file permission change was at least one of the causes ... it needs to be non-writable by group and world, otherwise the file is ignored.

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I think it's the cause in my case. But I didn't find any documentation about this. It's just my intuition that tells me something looks peculiar if I don't change the file permission... Is this documented anywhere?