@@ -36,6 +36,7 @@ jobs:
             configure: '--enable-zjit=dev'
             run_opts: '--zjit-call-threshold=1'
             specopts: '-T --zjit-call-threshold=1'
+            test_all_opts: '--seed=46450'
 
           - test_task: 'zjit-check' # zjit-test + quick feedback of test_zjit.rb
             configure: '--enable-yjit=dev --enable-zjit'
@@ -50,6 +51,7 @@ jobs:
       RUN_OPTS: ${{ matrix.run_opts }}
       SPECOPTS: ${{ matrix.specopts }}
       TESTOPTS: ${{ matrix.testopts }}
+      ZJIT_RB_BUG: 1
 
     runs-on: macos-14
 
@@ -117,9 +119,15 @@ jobs:
           TEST_BUNDLED_GEMS_ALLOW_FAILURES: ''
           SYNTAX_SUGGEST_TIMEOUT: '5'
           PRECHECK_BUNDLED_GEMS: 'no'
-          TESTS: ${{ matrix.tests }}
+          TESTS: ${{ matrix.test_all_opts }}
         continue-on-error: ${{ matrix.continue-on-test_task || false }}
 
+      - uses: ./.github/actions/slack
+        with:
+          label: ${{ matrix.test_task }} ${{ matrix.configure }}
+          SLACK_WEBHOOK_URL: ${{ secrets.SIMPLER_ALERTS_URL }} # ruby-lang slack: ruby/simpler-alerts-bot
+        if: ${{ failure() }}
+
   result:
     if: ${{ always() }}
     name: ${{ github.workflow }} result
 
@@ -55,6 +55,7 @@ jobs:
             configure: '--enable-zjit=dev'
             run_opts: '--zjit-call-threshold=1'
             specopts: '-T --zjit-call-threshold=1'
+            test_all_opts: '--seed=39471'
 
           - test_task: 'zjit-check' # zjit-test + quick feedback of test_zjit.rb
             configure: '--enable-yjit --enable-zjit=dev'
@@ -74,6 +75,7 @@ jobs:
       RUBY_DEBUG: ci
       BUNDLE_JOBS: 8 # for yjit-bench
       RUST_BACKTRACE: 1
+      ZJIT_RB_BUG: 1
 
     runs-on: ubuntu-22.04
 
@@ -159,9 +161,15 @@ jobs:
           SYNTAX_SUGGEST_TIMEOUT: '5'
           ZJIT_BINDGEN_DIFF_OPTS: '--exit-code'
           LIBCLANG_PATH: ${{ matrix.libclang_path }}
-          TESTS: ${{ matrix.tests }}
+          TESTS: ${{ matrix.test_all_opts }}
         continue-on-error: ${{ matrix.continue-on-test_task || false }}
 
+      - uses: ./.github/actions/slack
+        with:
+          label: ${{ matrix.test_task }} ${{ matrix.configure }}
+          SLACK_WEBHOOK_URL: ${{ secrets.SIMPLER_ALERTS_URL }} # ruby-lang slack: ruby/simpler-alerts-bot
+        if: ${{ failure() }}
+
   result:
     if: ${{ always() }}
     name: ${{ github.workflow }} result
 
@@ -161,6 +161,7 @@ The following default gems are updated.
 * bundler 2.8.0.dev
 * erb 5.0.2
 * etc 1.4.6
+* fcntl 1.3.0
 * io-console 0.8.1
 * io-nonblock 0.3.2
 * io-wait 0.3.2
 
@@ -40,14 +40,26 @@ concurrent_set_size(const void *ptr)
         (set->capacity * sizeof(struct concurrent_set_entry));
 }
 
+/* Hack: Though it would be trivial, we're intentionally avoiding WB-protecting
+ * this object. This prevents the object from aging and ensures it can always be
+ * collected in a minor GC.
+ * Longer term this deserves a better way to reclaim memory promptly.
+ */
+static void
+concurrent_set_mark(void *ptr)
+{
+    (void)ptr;
+}
+
 static const rb_data_type_t concurrent_set_type = {
     .wrap_struct_name = "VM/concurrent_set",
     .function = {
-        .dmark = NULL,
+        .dmark = concurrent_set_mark,
         .dfree = concurrent_set_free,
         .dsize = concurrent_set_size,
     },
-    .flags = RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED | RUBY_TYPED_EMBEDDABLE
+    /* Hack: NOT WB_PROTECTED on purpose (see above) */
+    .flags = RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_EMBEDDABLE
 };
 
 VALUE
 
@@ -388,7 +388,7 @@ There are multiple test suites:
 - `make test-all`
 - `make test-spec`
 - `make check` runs all of the above
-- `make yjit-smoke-test` runs quick checks to see that YJIT is working correctly
+- `make yjit-check` runs quick checks to see that YJIT is working correctly
 
 The tests can be run in parallel like this:
 
 
@@ -110,6 +110,49 @@ You can also run a single test case by matching the method name:
 make test-all TESTS="test/ruby/test_zjit.rb -n TestZJIT#test_putobject"
 ```
 
+## Statistics Collection
+
+ZJIT provides detailed statistics about JIT compilation and execution behavior.
+
+### Basic Stats
+
+Run with basic statistics printed on exit:
+
+```bash
+./miniruby --zjit-stats script.rb
+```
+
+Collect stats without printing (access via `RubyVM::ZJIT.stats` in Ruby):
+
+```bash
+./miniruby --zjit-stats=quiet script.rb
+```
+
+### Accessing Stats in Ruby
+
+```ruby
+# Check if stats are enabled
+if RubyVM::ZJIT.stats_enabled?
+  stats = RubyVM::ZJIT.stats
+  puts "Compiled ISEQs: #{stats[:compiled_iseq_count]}"
+  puts "Failed ISEQs: #{stats[:failed_iseq_count]}"
+
+  # You can also reset stats during execution
+  RubyVM::ZJIT.reset_stats!
+end
+```
+
+### Performance Ratio
+
+The `ratio_in_zjit` stat shows the percentage of Ruby instructions executed in JIT code vs interpreter. This metric only appears when ZJIT is built with `--enable-zjit=stats` (which enables `rb_vm_insn_count` tracking) and represents a key performance indicator for ZJIT effectiveness.
+
+To build with stats support:
+
+```bash
+./configure --enable-zjit=stats
+make -j
+```
+
 ## ZJIT Glossary
 
 This glossary contains terms that are helpful for understanding ZJIT.
 
@@ -65,7 +65,7 @@ pack up your own arguments to pass as args for locking functions, etc.
  *
  */
 
-#define FCNTL_VERSION "1.2.0"
+#define FCNTL_VERSION "1.3.0"
 
 void
 Init_fcntl(void)
@@ -251,4 +251,50 @@ Init_fcntl(void)
      */
     rb_define_const(mFcntl, "F_DUP2FD_CLOEXEC", INT2NUM(F_DUP2FD_CLOEXEC));
 #endif
+
+#ifdef F_PREALLOCATE
+    /*
+     * macOS specific flag used for preallocating file space.
+     */
+    rb_define_const(mFcntl, "F_PREALLOCATE", INT2NUM(F_PREALLOCATE));
+#endif
+
+#ifdef F_ALLOCATECONTIG
+    /*
+     * macOS specific flag used with F_PREALLOCATE for allocating contiguous
+     * space.
+     */
+    rb_define_const(mFcntl, "F_ALLOCATECONTIG", INT2NUM(F_ALLOCATECONTIG));
+#endif
+
+#ifdef F_ALLOCATEALL
+    /*
+     * macOS specific flag used with F_PREALLOCATE for allocating all contiguous
+     * space or no space.
+     */
+    rb_define_const(mFcntl, "F_ALLOCATEALL", INT2NUM(F_ALLOCATEALL));
+#endif
+
+#ifdef F_ALLOCATEPERSIST
+    /*
+     * macOS specific flag used with F_PREALLOCATE. Allocate space that is not
+     * freed when close is called.
+     */
+    rb_define_const(mFcntl, "F_ALLOCATEPERSIST", INT2NUM(F_ALLOCATEPERSIST));
+#endif
+
+#ifdef F_PEOFPOSMODE
+    /*
+     * macOS specific flag used with F_PREALLOCATE. Allocate from the physical
+     * end of file
+     */
+    rb_define_const(mFcntl, "F_PEOFPOSMODE", INT2NUM(F_PEOFPOSMODE));
+#endif
+
+#ifdef F_VOLPOSMODE
+    /*
+     * macOS specific flag used with F_PREALLOCATE. Allocate from the volume offset.
+     */
+    rb_define_const(mFcntl, "F_VOLPOSMODE", INT2NUM(F_VOLPOSMODE));
+#endif
 }
@@ -447,6 +447,11 @@ get_loaded_features_index(vm_ns_t *vm_ns)
         VALUE previous_realpath_map = rb_hash_dup(realpath_map);
         rb_hash_clear(realpaths);
         rb_hash_clear(realpath_map);
+
+        /* We have to make a copy of features here because the StringValue call
+         * below could call a Ruby method, which could modify $LOADED_FEATURES
+         * and cause it to be corrupt. */
+        features = rb_ary_resurrect(features);
         for (i = 0; i < RARRAY_LEN(features); i++) {
             VALUE entry, as_str;
             as_str = entry = rb_ary_entry(features, i);
@@ -456,6 +461,10 @@ get_loaded_features_index(vm_ns_t *vm_ns)
                 rb_ary_store(features, i, as_str);
             features_index_add(vm_ns, as_str, INT2FIX(i));
         }
+        /* The user modified $LOADED_FEATURES, so we should restore the changes. */
+        if (!rb_ary_shared_with_p(features, CURRENT_NS_LOADED_FEATURES(vm_ns))) {
+            rb_ary_replace(CURRENT_NS_LOADED_FEATURES(vm_ns), features);
+        }
         reset_loaded_features_snapshot(vm_ns);
 
         features = CURRENT_NS_LOADED_FEATURES_SNAPSHOT(vm_ns);