Update to the new fuel APIs introduced in bytecodealliance/wasmtime#7298. (#281)

Author: kpreisser

examples/consumefuel/Program.cs

@@ -12,7 +12,12 @@
     "expensive",
     Function.FromCallback(store, (Caller caller) =>
     {
-        var remaining = caller.ConsumeFuel(1000UL);
+        checked
+        {
+            caller.Fuel -= 1000UL;
+        }
+
+        var remaining = caller.Fuel;
         Console.WriteLine($"Called an expensive function which consumed 1000 fuel. {remaining} units of fuel remaining.");
     }
 ));
@@ -26,7 +31,7 @@
     return;
 }
 
-store.AddFuel(5000UL);
+store.Fuel += 5000UL;
 Console.WriteLine("Added 5000 units of fuel");
 
 for (var i = 0; i < 4; i++)

src/Caller.cs

@@ -137,33 +137,23 @@ public bool TryGetMemorySpan<T>(string name, long address, int length, out Span<
         public Store Store => store;
 
         /// <summary>
-        /// Adds fuel to this store for WebAssembly code to consume while executing.
+        /// Gets or sets the fuel available for WebAssembly code to consume while executing.
         /// </summary>
-        /// <param name="fuel">The fuel to add to the store.</param>
-        public void AddFuel(ulong fuel) => context.AddFuel(fuel);
-
-        /// <summary>
-        /// Synthetically consumes fuel from this store.
-        ///
-        /// For this method to work fuel consumption must be enabled via <see cref="Config.WithFuelConsumption(bool)"/>.
-        ///
+        /// <remarks>
+        /// <para>
+        /// For this property to work, fuel consumption must be enabled via <see cref="Config.WithFuelConsumption(bool)"/>.
+        /// </para>
+        /// <para>
         /// WebAssembly execution will automatically consume fuel but if so desired the embedder can also consume fuel manually
         /// to account for relative costs of host functions, for example.
-        ///
-        /// This method will attempt to consume <paramref name="fuel"/> units of fuel from within this store. If the remaining
-        /// amount of fuel allows this then the amount of remaining fuel is returned. Otherwise, a <see cref="WasmtimeException"/>
-        /// is thrown and no fuel is consumed.
-        /// </summary>
-        /// <param name="fuel">The fuel to consume from the store.</param>
-        /// <returns>Returns the remaining amount of fuel.</returns>
-        /// <exception cref="WasmtimeException">Thrown if more fuel is consumed than the store currently has.</exception>
-        public ulong ConsumeFuel(ulong fuel) => context.ConsumeFuel(fuel);
-
-        /// <summary>
-        /// Gets the fuel consumed by the executing WebAssembly code.
-        /// </summary>
-        /// <returns>Returns the fuel consumed by the executing WebAssembly code or 0 if fuel consumption was not enabled.</returns>
-        public ulong GetConsumedFuel() => context.GetConsumedFuel();
+        /// </para>
+        /// </remarks>
+        /// <value>The fuel available for WebAssembly code to consume while executing.</value>
+        public ulong Fuel
+        {
+            get => context.GetFuel();
+            set => context.SetFuel(value);
+        }
 
         /// <summary>
         /// Gets the user-defined data from the Store. 

src/Store.cs

@@ -20,9 +20,20 @@ internal void GC()
             Native.wasmtime_context_gc(handle);
         }
 
-        internal void AddFuel(ulong fuel)
+        internal ulong GetFuel()
         {
-            var error = Native.wasmtime_context_add_fuel(handle, fuel);
+            var error = Native.wasmtime_context_get_fuel(handle, out ulong fuel);
+            if (error != IntPtr.Zero)
+            {
+                throw WasmtimeException.FromOwnedError(error);
+            }
+
+            return fuel;
+        }
+
+        internal void SetFuel(ulong fuel)
+        {
+            var error = Native.wasmtime_context_set_fuel(handle, fuel);
             if (error != IntPtr.Zero)
             {
                 throw WasmtimeException.FromOwnedError(error);
@@ -49,27 +60,6 @@ internal Store Store
             }
         }
 
-        internal ulong ConsumeFuel(ulong fuel)
-        {
-            var error = Native.wasmtime_context_consume_fuel(handle, fuel, out var remaining);
-            if (error != IntPtr.Zero)
-            {
-                throw WasmtimeException.FromOwnedError(error);
-            }
-
-            return remaining;
-        }
-
-        internal ulong GetConsumedFuel()
-        {
-            if (!Native.wasmtime_context_fuel_consumed(handle, out var fuel))
-            {
-                return 0;
-            }
-
-            return fuel;
-        }
-
         internal void SetWasiConfiguration(WasiConfiguration config)
         {
             var wasi = config.Build();
@@ -97,14 +87,10 @@ private static class Native
             public static extern void wasmtime_context_gc(IntPtr handle);
 
             [DllImport(Engine.LibraryName)]
-            public static extern IntPtr wasmtime_context_add_fuel(IntPtr handle, ulong fuel);
+            public static extern IntPtr wasmtime_context_set_fuel(IntPtr handle, ulong fuel);
 
             [DllImport(Engine.LibraryName)]
-            public static extern IntPtr wasmtime_context_consume_fuel(IntPtr handle, ulong fuel, out ulong remaining);
-
-            [DllImport(Engine.LibraryName)]
-            [return: MarshalAs(UnmanagedType.I1)]
-            public static extern bool wasmtime_context_fuel_consumed(IntPtr handle, out ulong fuel);
+            public static extern IntPtr wasmtime_context_get_fuel(IntPtr handle, out ulong fuel);
 
             [DllImport(Engine.LibraryName)]
             public static extern IntPtr wasmtime_context_set_wasi(IntPtr handle, IntPtr config);
@@ -158,6 +144,35 @@ public Store(Engine engine, object? data)
             handle = new Handle(Native.wasmtime_store_new(engine.NativeHandle, (IntPtr)storeHandle, Finalizer));
         }
 
+        /// <summary>
+        /// Gets or sets the fuel available for WebAssembly code to consume while executing.
+        /// </summary>
+        /// <remarks>
+        /// <para>
+        /// For this property to work fuel consumption must be enabled via <see cref="Config.WithFuelConsumption(bool)"/>.
+        /// </para>
+        /// <para>
+        /// WebAssembly execution will automatically consume fuel but if so desired the embedder can also consume fuel manually
+        /// to account for relative costs of host functions, for example.
+        /// </para>
+        /// </remarks>
+        /// <value>The fuel available for WebAssembly code to consume while executing.</value>
+        public ulong Fuel
+        {
+            get
+            {
+                ulong fuel = Context.GetFuel();
+                System.GC.KeepAlive(this);
+                return fuel;
+            }
+
+            set
+            {
+                Context.SetFuel(value);
+                System.GC.KeepAlive(this);
+            }
+        }
+
         /// <summary>
         /// Limit the resources that this store may consume. Note that the limits are only used to limit the creation/growth of resources in the future,
         /// this does not retroactively attempt to apply limits to the store.
@@ -212,49 +227,6 @@ public void GC()
             System.GC.KeepAlive(this);
         }
 
-        /// <summary>
-        /// Adds fuel to this store for WebAssembly code to consume while executing.
-        /// </summary>
-        /// <param name="fuel">The fuel to add to the store.</param>
-        public void AddFuel(ulong fuel)
-        {
-            Context.AddFuel(fuel);
-            System.GC.KeepAlive(this);
-        }
-
-        /// <summary>
-        /// Synthetically consumes fuel from this store.
-        /// 
-        /// For this method to work fuel consumption must be enabled via <see cref="Config.WithFuelConsumption(bool)"/>.
-        /// 
-        /// WebAssembly execution will automatically consume fuel but if so desired the embedder can also consume fuel manually
-        /// to account for relative costs of host functions, for example.
-        /// 
-        /// This method will attempt to consume <paramref name="fuel"/> units of fuel from within this store. If the remaining
-        /// amount of fuel allows this then the amount of remaining fuel is returned. Otherwise, a <see cref="WasmtimeException"/>
-        /// is thrown and no fuel is consumed.
-        /// </summary>
-        /// <param name="fuel">The fuel to consume from the store.</param>
-        /// <returns>Returns the remaining amount of fuel.</returns>
-        /// <exception cref="WasmtimeException">Thrown if more fuel is consumed than the store currently has.</exception>
-        public ulong ConsumeFuel(ulong fuel)
-        {
-            var result = Context.ConsumeFuel(fuel);
-            System.GC.KeepAlive(this);
-            return result;
-        }
-
-        /// <summary>
-        /// Gets the fuel consumed by the executing WebAssembly code.
-        /// </summary>
-        /// <returns>Returns the fuel consumed by the executing WebAssembly code or 0 if fuel consumption was not enabled.</returns>
-        public ulong GetConsumedFuel()
-        {
-            var result = Context.GetConsumedFuel();
-            System.GC.KeepAlive(this);
-            return result;
-        }
-
         /// <summary>
         /// Configures WASI within the store.
         /// </summary>

tests/CallerTests.cs

@@ -30,7 +30,7 @@ public CallerTests(CallerFixture fixture)
         Linker = new Linker(Fixture.Engine);
         Store = new Store(Fixture.Engine);
 
-        Store.AddFuel(1000000);
+        Store.Fuel = 1000000;
     }
 
     [Fact]
@@ -309,11 +309,12 @@ public void ItCanSetData()
 
 
     [Fact]
-    public void ItCanConsumeFuel()
+    public void ItCanRemoveFuel()
     {
         Linker.DefineFunction("env", "callback", (Caller c) =>
         {
-            c.ConsumeFuel(10).Should().Be(1000000 - (10 + 2));
+            c.Fuel -= 10;
+            c.Fuel.Should().Be(1000000 - (10 + 2));
         });
 
         var instance = Linker.Instantiate(Store, Fixture.Module);
@@ -323,16 +324,16 @@ public void ItCanConsumeFuel()
 
         // 10 is consumed by the explicit fuel consumption
         // 2 is consumed by the rest of the WASM which executes behind the scenes in this test
-        Store.GetConsumedFuel().Should().Be(10 + 2);
+        Store.Fuel.Should().Be(1000000 - (10 + 2));
     }
 
     [Fact]
     public void ItCanAddFuel()
     {
         Linker.DefineFunction("env", "callback", (Caller c) =>
         {
-            c.AddFuel(2);
-            c.ConsumeFuel(0).Should().Be(1000000);
+            c.Fuel += 2;
+            c.Fuel.Should().Be(1000000);
         });
 
         var instance = Linker.Instantiate(Store, Fixture.Module);
@@ -341,15 +342,15 @@ public void ItCanAddFuel()
         callback.Invoke();
 
         // 2 is consumed by the WASM which executes behind the scenes in this test
-        Store.GetConsumedFuel().Should().Be(2);
+        Store.Fuel.Should().Be(1000000);
     }
 
     [Fact]
-    public void ItCanGetConsumedFuel()
+    public void ItCanGetFuel()
     {
         Linker.DefineFunction("env", "callback", (Caller c) =>
         {
-            c.GetConsumedFuel().Should().Be(2);
+            c.Fuel.Should().Be(1000000 - 2);
         });
 
         var instance = Linker.Instantiate(Store, Fixture.Module);