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Runtime startup performance improvements
The goal of this commit is to make Xamarin.Android apps start faster. The
changes are focused only around the very first stage of application startup -
between Android invoking our Java startup code (MonoPackageManager) and the end
of our `Runtime.init` (`Java_mono_android_Runtime_init` in the native runtime)
which is when the user application is fully initialized and ready to start is
launcher Activity.
In order to achieve the goal, the following changes were made:
* Java class lookup ("reflection").
We used to call the `FindClass` JNI function as part of the startup at a cost
of several milliseconds. We now put the class handles (accessed with the
`.class` Java accessor) in the `Runtime` class and initialize them from the
static constructor. We then read those fields from within `Runtime.init`,
which is passed a reference to the Java instance of the Runtime class.
Additonally, a handful of class field/method lookups were moved out of the
init code so that the code that doesn't use them doesn't have to pay the tax.
* Android API level is passed to `Runtime.init` from Java instead of using JNI
from the native code.
* Limit logging.
Previously whenever any of the `log_{info,debug}` functions were called we'd
spend time preparing all the parameters to pass to the function, sometimes
involving memory allocation, function calls, etc - only to discard all of
that work **inside** the `log_*` call because the logging category used in
that call was disabled. Now we check whether the category is enabled before
we set out to construct the parameters.
* Java/JNI type wrappers for string and array of strings.
This both a convenience/correctness as well as a performance change.
Introduced are two C++ wrapper classes for the `jstring` and `object array`
types (specialized for object == jstring) which take care of efficiently
caching the retrieved strings as well as of correctly deleting local
references to the obtained objects. Both classes, `jstring_wrapper` and
`jstring_array_wrapper` are optimized so that they compile into the
equivalent of the current, hand-written, code. They also take care to make
the minimum necessary number of calls in order to access the strings, both
standalone and from arrays, as well as to release the resources.
The string and array wrappers are passed around as references, thus using the
minimum amount of memory.
* Do not preload managed assemblies.
We used to preload all of the application assemblies in order to find and
invoke type initializers. This resulted in the list of assemblies being
processed twice at the great expense of time. We now don't call the type
initializers at all and the assemblies are loaded on demand.
* Do not store application environment variables in a file inside the apk.
The textual file used to be read from the apk(s) early in the process,
requiring iteration over all the application apk files, opening each of them,
browsing through the ZIP entries and, finally, reading the file line by line,
parsing into the name and value parts to create either a
property (`mono.aot`, `mono.llvm`) or any environment variables requested by
the application developer (or the XA runtime).
To speed the process up, this commit replaces the text file with a Java class
generated during application build which contains an array of `"name",
"value"` pairs. The class is passed to `Java_mono_android_Runtime_init` and
its elements are used to create the requested environment variables. A
handful of variables is special-cased in that they are not placed in the
environment but rather to set flags in the `AndroidSystem` class. The
variables are `mono.aot`, `mono.llvm` and `__XA_DSO_IN_APK`. This allowed to
remove calls to create (fake) system properties as well as `getenv` in the
init native function.
* Don't try load LLVM.so when it won't be there because we're not using llvm
* Convert package name to hash using optimized code without calling snprintf
* Desktop build is determined on compile time instead of dynamically
* xamarin_getifaddrs are initialized on demand, not at the startup.
Startup time improvements for the XF integration test app (average, Pixel 3 XL):
* Debug mode:
Old: 1s 440ms
New: 1s 100ms
* Release mode:
Old: 650ms
New: 270ms- Loading branch information
