| Filename | Latest commit message | Latest commit date |
|---|---|---|
2afef5070a
Convert BpfMap native methods to use @FastNative to reduce JNI overhead.
Refactor synchronizeKernelRCU() to be @CriticalNative for maximum
performance by changing its error handling to return an error code
instead of throwing directly from native code.
(In practice we don't expect it to *ever* fail)
FYI:
@FastNative and @CriticalNative are Android-specific annotations
that signal to the ART runtime to use a lower-overhead JNI transition,
resulting in better performance.
A standard JNI call tells the Garbage Collector (GC) that the thread
is transitioning to a 'Native' state. This is a signal to the GC that
the thread might be busy for a while and shouldn't be suspended arbitrarily.
@FastNative is for short, quick functions:
This provides a moderately faster JNI call (thread is still 'Runnable').
The native function signature remains the same as a standard JNI method,
and it can still access the JNIEnv* to interact with Java objects
or throw exceptions.
@CriticalNative is for short, quick & trivial functions:
This provides the fastest possible JNI transition and is intended
for simple, performance-critical leaf functions.
It comes with strict requirements:
- The native method cannot throw exceptions, create Java objects,
or make any other JNI calls.
- All arguments and the return type must be primitive, ie:
jboolean [bool]
jbyte [s8]
jchar [u16]
jshort [s16]
jint [s32]
jlong [s64]
jfloat [32-bit]
jdouble [64-bit]
void
Java objects like String or byte[] are not allowed.
Because of these restrictions, the native C++ function signature
must not include JNIEnv* or jobject/jclass parameters.
(This likely also means it must be 'static')
Test: TreeHugger
Flag: EXEMPT mainline
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I9b6107b26086df2e87218ff9274593e9f2eb6b0b
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||
| .. | ||
| bpfmapjni | ||
| bpfutiljni | ||
| commonconnectivityjni | ||
| ip_checksum | ||
| netjniutils | ||
| nettestutils | ||
| serviceconnectivityjni | ||
| tcutils | ||
| README.md | ||
JNI
As a general rule, jarjar every static library dependency used in a mainline module into the modules's namespace (especially if it is also used by other modules)
Fully-qualified name of java class needs to be hard-coded into the JNI .so, because JNI_OnLoad does not take any parameters. This means that there needs to be a different .so target for each post-jarjared package, so for each module.
This is the guideline to provide JNI library shared with modules:
-
provide a common java library in frameworks/libs/net with the Java class (e.g. BpfMap.java).
-
provide a common native library in frameworks/libs/net with the JNI and provide the native register function with class_name parameter. See register_com_android_net_module_util_BpfMap function in frameworks/libs/net/common/native/bpfmapjni/com_android_net_module_util_BpfMap.cpp as an example.
When you want to use JNI library from frameworks/lib/net:
-
Each module includes the java library (e.g. net-utils-device-common-bpf) and applies its jarjar rules after build.
-
Each module creates a native library in their directory, which statically links against the common native library (e.g. libnet_utils_device_common_bpf), and calls the native registered function by hardcoding the post-jarjar class_name. Linkage MUST be static because common functions in the file (e.g.,
register_com_android_net_module_util_BpfMap) will appear in the library (.so) file, and different versions of the library loaded in the same process by different modules will in general have different versions. It's important that each of these libraries loads the common function from its own library. Static linkage should guarantee this because static linkage resolves symbols at build time, not runtime.