Introduce HeapSize()

This PR adds the possibility to determine for a chain of
eventuals the maximum amount of heap memory that needs to
get allocated.

eventuals/closure.h

@@ -5,6 +5,7 @@
 #include "eventuals/compose.h"
 #include "eventuals/interrupt.h"
 #include "eventuals/type-erased-stream.h"
+#include "stout/bytes.h"
 
 ////////////////////////////////////////////////////////////////////////
 
@@ -63,6 +64,10 @@ struct _Closure final {
       return *continuation_;
     }
 
+    Bytes HeapSize() {
+      return Bytes{0} + k_.HeapSize();
+    }
+
     F_ f_;
 
     Interrupt* interrupt_ = nullptr;

eventuals/eventual.h

@@ -6,6 +6,7 @@
 #include "eventuals/interrupt.h"
 #include "eventuals/scheduler.h"
 #include "eventuals/undefined.h"
+#include "stout/bytes.h"
 
 // TODO(benh): catch exceptions from 'start', 'fail', 'stop', etc.
 
@@ -170,6 +171,10 @@ struct _Eventual {
       return adaptor_;
     }
 
+    Bytes HeapSize() {
+      return Bytes{0} + k_.HeapSize();
+    }
+
     Context_ context_;
     Start_ start_;
     Fail_ fail_;

eventuals/scheduler.h

@@ -15,6 +15,7 @@
 #include "eventuals/terminal.h"
 #include "eventuals/undefined.h"
 #include "stout/borrowable.h"
+#include "stout/bytes.h"
 #include "stout/stringify.h"
 
 ////////////////////////////////////////////////////////////////////////
@@ -392,6 +393,10 @@ struct Reschedulable final {
     interrupt_ = &interrupt;
   }
 
+  Bytes HeapSize() {
+    return Bytes{0} + k_.HeapSize();
+  }
+
   Interrupt* interrupt_ = nullptr;
 
   using Continuation_ =
@@ -471,6 +476,10 @@ struct _Preempt final {
       }
     }
 
+    Bytes HeapSize() {
+      return Bytes{0} + k_.HeapSize();
+    }
+
     Scheduler::Context context_;
 
     E_ e_;

eventuals/terminal.h

@@ -3,6 +3,7 @@
 #include "eventuals/compose.h"
 #include "eventuals/interrupt.h"
 #include "eventuals/undefined.h"
+#include "stout/bytes.h"
 
 ////////////////////////////////////////////////////////////////////////
 
@@ -57,6 +58,10 @@ struct _Terminal final {
 
     void Register(Interrupt&) {}
 
+    Bytes HeapSize() {
+      return Bytes{0};
+    }
+
     Context_ context_;
     Start_ start_;
     Fail_ fail_;

test/eventual.cc

@@ -332,5 +332,21 @@ TEST(EventualTest, Ref) {
   EXPECT_EQ(110, x);
 }
 
+TEST(EventualTest, HeapSize) {
+  auto e = []() {
+    return Eventual<int>([](auto& k) {
+      k.Start(1);
+    });
+  };
+
+  auto [future, k] = PromisifyForTest(e());
+
+  k.Start();
+
+  EXPECT_EQ(0, k.HeapSize().bytes());
+
+  EXPECT_EQ(1, future.get());
+}
+
 } // namespace
 } // namespace eventuals::test