I realized that some builds may crash if we automatically close the
classloaders. While I do think that is a good thing in general that we
are closing the loaders by default, we shuold have an option for
supressing this behavior.
I made all of the custom classloaders that we define for test and run
check this property before calling the super.close method.
We want to notify users about the new features available in sbt 1.3.0 to
increase visibility. Turbo mode especially can benefit many builds, but
we have opted to leave it off by default for now.
The banner will be displayed the first time sbt enters the shell command
on each sbt run. The banner can be disabled globally with the sbt.banner
system property. It can be displayed on a per sbt version by running the
skipWelcomeBanner command. That command touches a file in the ~/.sbt/1.0
directory to make it persistent across all projects.
I decided creations/deletions/updates were a bit too technical rather
than descriptive. It also wasn't really correct to say Meta build
sources because the meta build is the build for the build. Instead, I
dropped Meta from the sentence. I also made the instructions when
changed sources are detected more active. I left them capitalized since
they are instructions rather than warnings.
Apply these changes by running `reload`.
Automatically reload the build when source changes are detected by setting `Global / onChangedBuildSource := ReloadOnSourceChanges`.
Disable this warning by setting `Global / onChangedBuildSource := IgnoreSourceChanges`.
Also indentation was wrong for the printed files when multiple files had
changed because the mkString middle argument was " \n" rather than "\n ".
This creates a performance mode that enables experimental or advanced features that might require some debugging by the build user when it doesn't work.
Initially we are putting the layered ClassLoader (`ClassLoaderLayeringStrategy.AllLibraryJars`) behind this flag.
We now correctly close the test classloader which can cause this
scripted test to fail if the classloader is closed before the actor
system finishes terminating.
At some point I noticed that projects with no scala sources in the build
loaded significantly faster than projects that had even a single scala
file -- no matter how simple that file was. This didn't really make
sense to me because *.sbt files _do_ have to be compiled. I finally
realized that classloading was a likely bottle neck because *.sbt
files are compiled on the sbt classpath while *.scala files are compiled
with a different classloader generated by the classloader cache. It then
occurred to me that we could pre-fill the classloader cache with the
scala layer of the sbt metabuild classloader.
I found that compared to 1.3.0-M5, a project with a simple scala file in
the project directory loaded about 2 seconds faster after this change.
Even if there are no scala sources in the build.sbt, there is a similar
performance improvement for running "sbt compile", which I found exited
2-3 seconds faster after this change.
My first attempt, cc8c66c66d, at making
java reflection work with a layered classloader with a dependency jar
layer was a failure. It would generally work ok the first time the user
ran test, but was likely to fail on a second run.
There were a number of problems with the strategy:
1) It relied on the thread's context class loader to determine where to
attempt the reverse lookup.
2) It is not possible to ever reload classes loaded by a classloader.
Consider the classloading hierarchy a <- b, where
the arrow implies that a is the parent of b. I incorrectly thought
that a's loadClass method would be called every time a class loaded
by a made a call to Class.forName(name: String). This turns out to
not be the case. As a result, the second time the dependency layer
was used, where now the hierarchy is a <- c, that same Class.forName
call could return a Class from b which causes a nasty crash.
It isn't possible to work around the limitation in 2 so the only option
that allows both caching and java reflection across layers to work is to
cache the dependency layer, but invalidate when cross layer reflection
occurs. This turns out to be straightforward to implement. The
performance looks very similar to the ScalaLibrary strategy when java
reflection is used, which makes sense because the scala library and
scala reflect layers are still reused when the dependency layer is
invalidated.
I also stopped passing around the resource map to all of the layers.
Resource loading is hierarchical and the resource layer comes above the
dependency layer in the stack so there was no need for the bottom layers
to also be RawResource loaders.
While testing some classloader changes, I realized that we didn't always
close the test classloaders because they didn't necessarily extend
URLClassLoader, but instead implemented AutoCloseable.
Bonus: don't set the context classloader. It turns out that the test
framework does that anyway inside of trl.run so it was pointless to do
in Defaults.scala.
The Reload exception that I added in the sbt package really wasn't
intended to be public. It's only meant to be used by
checkMetaBuildSources, which the users shouldn't override. I put it in
the top package though because I wanted it to be next to FullReload. I
also am not sure why the Reload object in Watch was private[sbt], but
while writing documentation, I realized that users couldn't access it.
While writing documentation for the watch subsystem, I realized that
it's awkward to configure watch to clear the screen before task
evaluation. To make this easier, I added a setting watchBeforeCommand
which is an arbitrary function that will run before the watch process
evaluates the command(s).
I also added helper functions for adding clear screen functionality.
I also realized that we weren't using the watchOnEnter or
watchOnExit callbacks anywhere. I had added these to support setting up
some state before watch starts and cleaning it up before it exits for
plugin authors. It makes sense to remove that functionality for 1.3.0
and only if a need presents itself re-add it in a later version of sbt.
I also made a few apis private[sbt] that I'm not sure about. Writing
documentation made me realize that some of these are redundant and/or
not ready for general consumption.
I had previously set some of the watch settings at the global level and
some at the project level. While writing documentation for the new watch
subsystem, I realized that the defaults should be set globally so that
they can be overridden at the ThisBuild level.
I also moved watchTriggers to sbt.nio.Keys. It was an oversight that it
wasn't moved there in a5cefd45be.
The classpath filter for test and run was added in #661 to ensure that
the classloaders were correctly isolated. That is no longer necessary
with the new layering strategies that are more precise about which jars
are exposed at each level. Using the filtered classloader was causing
the reflection used by spark to fail when using java 11.
This test ensures that a simple spark app will work with all of the
classloader layering strategies. Spark is an important part of the scala
ecosystem and heavily taxes classloading.
The test just checks that the app runs. I verified manually that the
first time that run is evaluated takes about 8 seconds regardless of the
layering strategy. It drops to 6 seconds with the ScalaLibrary strategy.
It drops to 1 seconds with AllLibraryJars.
We were incorrectly building the dependency layer in the run task using
the raw jars from dependencyClasspath rather than the actual classpath
jars (which may be different if bgCopyClasspath is true -- which it is
by default). This was preventing spark from working with AllLibraryJars
because it would load its classes and resources from the coursier cache
but the classpath filter would reject the resources because they came
from the coursier cache instead of the classpath.
The docs for ClassLoader,
https://docs.oracle.com/javase/8/docs/api/java/lang/ClassLoader.html
say that all non-hierarchical custom classloaders should be registered
as parallel capable. The docs also suggest that custom classloaders
should try to only override findClass so I reworked LayerdClassLoader to
only override findClass. I also added locking to the class loading to
make it safe for concurrent loading.
All of the custom classloaders besides LayeredClassLoader either
subclass URLClassLoader or LayeredClassLoader but don't override
loadClass. Because those two classloaders are parallel capable, the
subclasses should be as well. It isn't possible to make classloaders
that are implemented in scala parallel capable because scala 2 doesn't
support jvm static blocks (dotty does support this with an annotation).
To work around this, I re-worked some of the classloaders so that they
are either directly implemented in java or I subclassed a scala
implementation class in java.
Jave reflection did not work with layered classloaders if a dependency
attempted to load a class that was below the dependency layer in the
layered classloader hierarchy. The underlying problem was (in general) a
call to Class.forName somewhere. If the classloader parameter is not
specified, then Class.forName locates the ClassLoader for the caller
using reflection. It ultimately delegates to that ClassLoader's
loadClass method. With the previous LayeredClassLoader class, there was
no way for that classloader to access a URL that was below it in the
class loading hierarchy. I reworked LayeredClassLoader so that if it
fails to load the class, it will check the Thread's context classloader
and see if there are other LayeredClassLoader instances below it. If so,
it will then check if any of those classloaders would be able to load
the class by using findResource. If the descendant loader can load the
class, then we manually load it with findClass.
For best caching performance, we want to use the scala-reflect.jar that
is found in the scala instance. Also, in the runtime configuration,
caching didn't work correctly because we filtered the scala reflect
library from the dependency jars. We really only wanted to filter out
the library jars.
It also was problematic to use a LayeredClassLoader for the scala
reflect layer because in a subsequent commit I add the capability for a
layered classloader to load classes from its descendant loaders. This
caused problems when the scala-reflect layer was a LayeredClassLoader.
Instead, I add the ScalaReflectClassLoader class for better reporting.
Eugene Yokota
Ethan Atkins
Akhtyam Sakaev
Dale Wijnand