feat(core): Deno.core.heapStats() (#9659)

This commit implements "Deno.core.heapStats()" function 
that allows to programatically measure isolate heap-usage.

5 files changed, 149 insertions, 0 deletions

diff --git a/cli/tests/heapstats.js b/cli/tests/heapstats.js
new file mode 100644
index 000000000..0ed623e56
--- /dev/null
+++ b/cli/tests/heapstats.js
@@ -0,0 +1,36 @@
+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+"use strict";
+
+function allocTest(alloc, allocAssert, deallocAssert) {
+  // Helper func that GCs then returns heapStats
+  const sample = () => {
+    // deno-lint-ignore no-undef
+    gc();
+    return Deno.core.heapStats();
+  };
+  const delta = (t1, t2) => t2.usedHeapSize - t1.usedHeapSize;
+
+  // Sample "clean" heapStats
+  const t1 = sample();
+
+  // Alloc
+  let x = alloc();
+  const t2 = sample();
+  allocAssert(delta(t1, t2));
+
+  // Free
+  x = null;
+  const t3 = sample();
+  deallocAssert(delta(t2, t3));
+}
+
+function main() {
+  // Large-array test, 1M slot array consumes ~4MB (4B per slot)
+  allocTest(
+    () => new Array(1e6),
+    (delta) => console.log("Allocated:", Math.round(delta / 1e6) + "MB"),
+    (delta) => console.log("Freed:", Math.round(delta / 1e6) + "MB"),
+  );
+}
+
+main();
diff --git a/cli/tests/heapstats.js.out b/cli/tests/heapstats.js.out
new file mode 100644
index 000000000..b75a755f8
--- /dev/null
+++ b/cli/tests/heapstats.js.out
@@ -0,0 +1,2 @@
+Allocated: 4MB
+Freed: -4MB
diff --git a/cli/tests/integration_tests.rs b/cli/tests/integration_tests.rs
index e7fc7797b..96223c438 100644
--- a/cli/tests/integration_tests.rs
+++ b/cli/tests/integration_tests.rs
@@ -3217,6 +3217,11 @@ console.log("finish");
     output: "exit_error42.ts.out",
   });
 
+  itest!(heapstats {
+    args: "run --quiet --v8-flags=--expose-gc heapstats.js",
+    output: "heapstats.js.out",
+  });
+
   itest!(https_import {
     args: "run --quiet --reload --cert tls/RootCA.pem https_import.ts",
     output: "https_import.ts.out",
diff --git a/core/bindings.rs b/core/bindings.rs
index 23cd86a17..c5ed5b601 100644
--- a/core/bindings.rs
+++ b/core/bindings.rs
@@ -59,6 +59,9 @@ lazy_static! {
       v8::ExternalReference {
         function: get_proxy_details.map_fn_to()
       },
+      v8::ExternalReference {
+        function: heap_stats.map_fn_to(),
+      },
     ]);
 }
 
@@ -135,6 +138,7 @@ pub fn initialize_context<'s>(
   set_func(scope, core_val, "deserialize", deserialize);
   set_func(scope, core_val, "getPromiseDetails", get_promise_details);
   set_func(scope, core_val, "getProxyDetails", get_proxy_details);
+  set_func(scope, core_val, "heapStats", heap_stats);
 
   let shared_key = v8::String::new(scope, "shared").unwrap();
   core_val.set_accessor(scope, shared_key.into(), shared_getter);
@@ -923,3 +927,102 @@ fn throw_type_error(scope: &mut v8::HandleScope, message: impl AsRef<str>) {
   let exception = v8::Exception::type_error(scope, message);
   scope.throw_exception(exception);
 }
+
+fn heap_stats(
+  scope: &mut v8::HandleScope,
+  _args: v8::FunctionCallbackArguments,
+  mut rv: v8::ReturnValue,
+) {
+  fn set_prop(
+    scope: &mut v8::HandleScope,
+    obj: v8::Local<v8::Object>,
+    name: &'static str,
+    value: usize,
+  ) {
+    let key = v8::String::new(scope, name).unwrap();
+    let val = v8::Number::new(scope, value as f64);
+    obj.set(scope, key.into(), val.into());
+  }
+
+  let s = get_heap_stats(scope);
+
+  // TODO: use serde for this once we have serde_v8
+  let obj = v8::Object::new(scope);
+  set_prop(scope, obj, "totalHeapSize", s.total_heap_size);
+  set_prop(
+    scope,
+    obj,
+    "totalHeapSizexecutable",
+    s.total_heap_size_executable,
+  );
+  set_prop(scope, obj, "totalPhysicalSize", s.total_physical_size);
+  set_prop(scope, obj, "totalAvailableSize", s.total_available_size);
+  set_prop(
+    scope,
+    obj,
+    "totalGlobalHandlesSize",
+    s.total_global_handles_size,
+  );
+  set_prop(
+    scope,
+    obj,
+    "usedGlobalHandlesSize",
+    s.used_global_handles_size,
+  );
+  set_prop(scope, obj, "usedHeapSize", s.used_heap_size);
+  set_prop(scope, obj, "heapSizeLimit", s.heap_size_limit);
+  set_prop(scope, obj, "mallocedMemory", s.malloced_memory);
+  set_prop(scope, obj, "externalMemory", s.external_memory);
+  set_prop(scope, obj, "peakMallocedMemory", s.peak_malloced_memory);
+  set_prop(
+    scope,
+    obj,
+    "numberOfNativeContexts",
+    s.number_of_native_contexts,
+  );
+  set_prop(
+    scope,
+    obj,
+    "numberOfDetachedContexts",
+    s.number_of_detached_contexts,
+  );
+
+  rv.set(obj.into());
+}
+
+// HeapStats stores values from a isolate.get_heap_statistics() call
+struct HeapStats {
+  total_heap_size: usize,
+  total_heap_size_executable: usize,
+  total_physical_size: usize,
+  total_available_size: usize,
+  total_global_handles_size: usize,
+  used_global_handles_size: usize,
+  used_heap_size: usize,
+  heap_size_limit: usize,
+  malloced_memory: usize,
+  external_memory: usize,
+  peak_malloced_memory: usize,
+  number_of_native_contexts: usize,
+  number_of_detached_contexts: usize,
+}
+fn get_heap_stats(isolate: &mut v8::Isolate) -> HeapStats {
+  let mut s = v8::HeapStatistics::default();
+  isolate.get_heap_statistics(&mut s);
+
+  HeapStats {
+    total_heap_size: s.total_heap_size(),
+    total_heap_size_executable: s.total_heap_size_executable(),
+    total_physical_size: s.total_physical_size(),
+    total_available_size: s.total_available_size(),
+    total_global_handles_size: s.total_global_handles_size(),
+    used_global_handles_size: s.used_global_handles_size(),
+    used_heap_size: s.used_heap_size(),
+    heap_size_limit: s.heap_size_limit(),
+    malloced_memory: s.malloced_memory(),
+    external_memory: s.external_memory(),
+    peak_malloced_memory: s.peak_malloced_memory(),
+    number_of_native_contexts: s.number_of_native_contexts(),
+    number_of_detached_contexts: s.number_of_detached_contexts(),
+  }
+}
diff --git a/core/lib.deno_core.d.ts b/core/lib.deno_core.d.ts
index 1efb92dc6..004ed0529 100644
--- a/core/lib.deno_core.d.ts
+++ b/core/lib.deno_core.d.ts
@@ -35,5 +35,8 @@ declare namespace Deno {
 
     /** Close the resource with the specified op id. */
     function close(rid: number): void;
+
+    /** Get heap stats for current isolate/worker */
+    function heapStats(): Record<string, number>;
   }
 }