Introduce MockVM (#1049)

This PR introduces `MockVM`, a type that implements `VMBinding` and
allows users to control the behavior of each method for testing. This PR
also moves all the tests in the current `DummyVM` to `MockVM`, and
removes the current `DummyVM`.

This PR closes #99. Note that
the current `MockVM` implementation does not allow changing constants or
associated types in `VMBinding` -- I would suggest we create another
issue to track this problem.

Changes:
* Introduce `MockVM`, and write all the current `DummyVM` tests with
`MockVM`.
* Remove `DummyVM`, and remove `./examples` which uses `DummyVM`.
* Change CI scripts to run tests with `MockVM`.
* Remove `pub` visibility for some modules. Those modules were exposed
so we can test them from `DummyVM`. As now `MockVM` is a part of the
main crate, we can test private items. We no longer need `pub` for those
modules.

.github/scripts/ci-style.sh

@@ -27,6 +27,11 @@ if [[ $arch == "x86_64" && $os == "linux" ]]; then
     cargo clippy --tests --features perf_counter
 fi
 
+# mock tests
+cargo clippy --features mock_test
+cargo clippy --features mock_test --tests
+cargo clippy --features mock_test --benches
+
 # --- Check auxiliary crate ---
 
 style_check_auxiliary_crate() {
@@ -37,4 +42,3 @@ style_check_auxiliary_crate() {
 }
 
 style_check_auxiliary_crate macros
-style_check_auxiliary_crate vmbindings/dummyvm

.github/scripts/ci-test.sh

@@ -11,35 +11,29 @@ if [[ $arch == "x86_64" && $os == "linux" ]]; then
     cargo test --features perf_counter
 fi
 
-./examples/build.py
-
 ALL_PLANS=$(sed -n '/enum PlanSelector/,/}/p' src/util/options.rs | sed -e 's;//.*;;g' -e '/^$/d' -e 's/,//g' | xargs | grep -o '{.*}' | grep -o '\w\+')
 
-# Test with DummyVM (each test in a separate run)
-cd vmbindings/dummyvm
-for fn in $(ls src/tests/*.rs); do
-    t=$(basename -s .rs $fn)
-
-    if [[ $t == "mod" ]]; then
-        continue
-    fi
+# Test with mock VM:
+# - Find all the files that start with mock_test_
+# - Run each file separately with cargo test, with the feature 'mock_test'
+find ./src ./tests -type f -name "mock_test_*" | while read -r file; do
+    t=$(basename -s .rs $file)
 
     # Get the required plans.
     # Some tests need to be run with multiple plans because
     # some bugs can only be reproduced in some plans but not others.
-    PLANS=$(sed -n 's/^\/\/ *GITHUB-CI: *MMTK_PLAN=//p' $fn)
+    PLANS=$(sed -n 's/^\/\/ *GITHUB-CI: *MMTK_PLAN=//p' $file)
     if [[ $PLANS == 'all' ]]; then
         PLANS=$ALL_PLANS
     elif [[ -z $PLANS ]]; then
         PLANS=NoGC
     fi
 
     # Some tests need some features enabled.
-    FEATURES=$(sed -n 's/^\/\/ *GITHUB-CI: *FEATURES=//p' $fn)
+    FEATURES=$(sed -n 's/^\/\/ *GITHUB-CI: *FEATURES=//p' $file)
 
     # Run the test with each plan it needs.
     for MMTK_PLAN in $PLANS; do
-        env MMTK_PLAN=$MMTK_PLAN cargo test --features "$FEATURES" -- $t;
+        env MMTK_PLAN=$MMTK_PLAN cargo test --features mock_test,"$FEATURES" -- $t;
     done
 done
-

Cargo.toml

@@ -54,17 +54,26 @@ sysinfo = "0.29"
 [dev-dependencies]
 paste = "1.0.8"
 rand = "0.8.5"
+criterion = "0.4"
 
 [build-dependencies]
 built = { version = "0.7.1", features = ["git2"] }
 
+[[bench]]
+name = "main"
+harness = false
+
 [features]
 default = []
 
 # This feature is only supported on x86-64 for now
 # It's manually added to CI scripts
 perf_counter = ["pfm"]
 
+# This feature is only used for tests with MockVM.
+# CI scripts run those tests with this feature.
+mock_test = []
+
 # .github/scripts/ci-common.sh extracts features from the following part (including from comments).
 # So be careful when editing or adding stuff to the section below.
 

benches/alloc.rs

@@ -0,0 +1,17 @@
+use criterion::Criterion;
+
+use mmtk::memory_manager;
+use mmtk::util::test_util::fixtures::*;
+use mmtk::AllocationSemantics;
+
+pub fn bench(c: &mut Criterion) {
+    // Disable GC so we won't trigger GC
+    let mut fixture = MutatorFixture::create_with_heapsize(1 << 30);
+    memory_manager::disable_collection(fixture.mmtk());
+    c.bench_function("alloc", |b| {
+        b.iter(|| {
+            let _addr =
+                memory_manager::alloc(&mut fixture.mutator, 8, 8, 0, AllocationSemantics::Default);
+        })
+    });
+}

benches/main.rs

@@ -0,0 +1,37 @@
+use criterion::criterion_group;
+use criterion::criterion_main;
+use criterion::Criterion;
+
+// As we can only initialize one MMTk instance, we have to run each benchmark in a separate process.
+// So we only register one benchmark to criterion ('bench_main'), and based on the env var MMTK_BENCH,
+// we pick the right benchmark to run.
+
+// The benchmark can be executed with the following command. The feature `mock_test` is required, as the tests use MockVM.
+// MMTK_BENCH=alloc cargo bench --features mock_test
+// MMTK_BENCH=sft   cargo bench --features mock_test
+
+// [Yi] I am not sure if these benchmarks are helpful any more after the MockVM refactoring. MockVM is really slow, as it
+// is accessed with a lock, and it dispatches every call to function pointers in a struct. These tests may use MockVM,
+// so they become slower as well. And the slowdown
+// from MockVM may hide the actual performance difference when we change the functions that are benchmarked.
+// We may want to improve the MockVM implementation so we can skip dispatching for benchmarking, or introduce another MockVM
+// implementation for benchmarking.
+// However, I will just keep these benchmarks here. If we find it not useful, and we do not plan to improve MockVM, we can delete
+// them.
+
+mod alloc;
+mod sft;
+
+fn bench_main(c: &mut Criterion) {
+    match std::env::var("MMTK_BENCH") {
+        Ok(bench) => match bench.as_str() {
+            "alloc" => alloc::bench(c),
+            "sft" => sft::bench(c),
+            _ => panic!("Unknown benchmark {:?}", bench),
+        },
+        Err(_) => panic!("Need to name a benchmark by the env var MMTK_BENCH"),
+    }
+}
+
+criterion_group!(benches, bench_main);
+criterion_main!(benches);

benches/sft.rs

@@ -0,0 +1,19 @@
+use criterion::black_box;
+use criterion::Criterion;
+
+use mmtk::memory_manager;
+use mmtk::util::test_util::fixtures::*;
+use mmtk::util::test_util::mock_vm::*;
+use mmtk::vm::ObjectModel;
+use mmtk::vm::VMBinding;
+use mmtk::AllocationSemantics;
+
+pub fn bench(c: &mut Criterion) {
+    let mut fixture = MutatorFixture::create();
+    let addr = memory_manager::alloc(&mut fixture.mutator, 8, 8, 0, AllocationSemantics::Default);
+    let obj = <MockVM as VMBinding>::VMObjectModel::address_to_ref(addr);
+
+    c.bench_function("sft read", |b| {
+        b.iter(|| memory_manager::is_in_mmtk_spaces::<MockVM>(black_box(obj)))
+    });
+}

docs/userguide/src/portingguide/perf_tuning/alloc.md

@@ -33,7 +33,7 @@ If the VM is not implemented in Rust,
 the binding needs to turn the boxed pointer into a raw pointer before storing it.
 
 ```rust
-{{#include ../../../../../vmbindings/dummyvm/src/tests/doc_mutator_storage.rs:mutator_storage_boxed_pointer}}
+{{#include ../../../../../src/vm/tests/mock_tests/mock_test_doc_mutator_storage.rs:mutator_storage_boxed_pointer}}
 ```
 
 ### Option 2: Embed the `Mutator` struct
@@ -44,7 +44,7 @@ If the implementation language is not Rust, the developer needs to create a type
 have an assertion to ensure that the native type has the exact same layout as the Rust type `Mutator`.
 
 ```rust
-{{#include ../../../../../vmbindings/dummyvm/src/tests/doc_mutator_storage.rs:mutator_storage_embed_mutator_struct}}
+{{#include ../../../../../src/vm/tests/mock_tests/mock_test_doc_mutator_storage.rs:mutator_storage_embed_mutator_struct}}
 ```
 
 ### Option 3: Embed the fast-path struct
@@ -78,7 +78,7 @@ which includes (but not limited to) `NoGC`, `SemiSpace`, `Immix`, generational p
 If a plan does not do bump-pointer allocation, we may still implement fast-paths, but we need to embed different data structures instead of `BumpPointer`.
 
 ```rust
-{{#include ../../../../../vmbindings/dummyvm/src/tests/doc_mutator_storage.rs:mutator_storage_embed_fast-path_struct}}
+{{#include ../../../../../src/vm/tests/mock_tests/mock_test_doc_mutator_storage.rs:mutator_storage_embed_fastpath_struct}}
 ```
 
 And pseudo-code for how you would reset the `BumpPointer`s for all mutators in `resume_mutators`. Note that these mutators are the runtime's actual mutator threads (i.e. where the cached bump pointers are stored) and are different from MMTk's `Mutator` struct.
@@ -120,7 +120,7 @@ Once MMTk is initialized, a binding can get the memory offset for the default al
 with the default allocation semantics, we can use the offset to get a reference to the actual allocator (with unsafe code), and allocate with the allocator.
 
 ```rust
-{{#include ../../../../../vmbindings/dummyvm/src/tests/doc_avoid_resolving_allocator.rs:avoid_resolving_allocator}}
+{{#include ../../../../../src/vm/tests/mock_tests/mock_test_doc_avoid_resolving_allocator.rs:avoid_resolving_allocator}}
 ```
 
 ## Emitting Allocation Sequence in a JIT Compiler