doc(examples): Add Global examples

Cargo.toml

@@ -191,6 +191,16 @@ name = "exported-function"
 path = "examples/exports_function.rs"
 required-features = ["cranelift"]
 
+[[example]]
+name = "exported-global"
+path = "examples/exports_global.rs"
+required-features = ["cranelift"]
+
+[[example]]
+name = "imported-global"
+path = "examples/imports_global.rs"
+required-features = ["cranelift"]
+
 [[example]]
 name = "wasi"
 path = "examples/wasi.rs"

examples/README.md

@@ -150,8 +150,23 @@ example.
    </details>
 
 ### Exports
+
+8. [**Exported global**][exported-global], explains how to work with
+   exported globals: get/set their value, have information about their 
+   type.
 
-8. [**Exported function**][exported-function], explains how to get and
+   _Keywords_: export, global.
+
+   <details>
+   <summary><em>Execute the example</em></summary>
+
+   ```shell
+   $ cargo run --example exported-globals --release --features "cranelift"
+   ```
+
+   </details>
+
+9. [**Exported function**][exported-function], explains how to get and
    how to call an exported function. They come in 2 flavors: dynamic,
    and “static”/native. The pros and cons are discussed briefly.
 
@@ -166,9 +181,25 @@ example.
 
    </details>
 
+### Imports
+
+10. [**Imported global**][imported-global], explains how to work with
+   imported globals: create globals, import them, get/set their value.
+
+   _Keywords_: import, global.
+
+   <details>
+   <summary><em>Execute the example</em></summary>
+
+   ```shell
+   $ cargo run --example imported-globals --release --features "cranelift"
+   ```
+
+   </details>
+
 ### Integrations
 
-9. [**WASI**][wasi], explains how to use the [WebAssembly System
+11. [**WASI**][wasi], explains how to use the [WebAssembly System
    Interface][WASI] (WASI), i.e. the [`wasmer-wasi`] crate.
 
    _Keywords_: wasi, system, interface
@@ -189,7 +220,9 @@ example.
 [compiler-cranelift]: ./compiler_cranelift.rs
 [compiler-llvm]: ./compiler_llvm.rs
 [cross-compilation]: ./engine_cross_compilation.rs
+[exported-global]: ./exports_global.rs
 [exported-function]: ./exports_function.rs
+[imported-global]: imports_global.rs
 [wasi]: ./wasi.rs
 [`wasmer-compiler-singlepass`]: https://github.com/wasmerio/wasmer/tree/master/lib/compiler-singlepass
 [`wasmer-compiler-cranelift`]: https://github.com/wasmerio/wasmer/tree/master/lib/compiler-cranelift

examples/exports_global.rs

@@ -0,0 +1,143 @@
+//! A Wasm module can export entities, like functions, memories,
+//! globals and tables.
+//!
+//! This example illustrates how to use exported globals. They come
+//! in 2 flavors:
+//!
+//!   1. Immutable globals (const),
+//!   2. Mutable globals.
+//!
+//! You can run the example directly by executing in Wasmer root:
+//!
+//! ```shell
+//! cargo run --example exported-global --release --features "cranelift"
+//! ```
+//!
+//! Ready?
+
+use wasmer::{imports, wat2wasm, Instance, Module, Mutability, Store, Type, Value};
+use wasmer_compiler_cranelift::Cranelift;
+use wasmer_engine_jit::JIT;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    // Let's declare the Wasm module with the text representation.
+    let wasm_bytes = wat2wasm(
+        br#"
+(module
+  (global $one (export "one") f32 (f32.const 1))
+  (global $some (export "some") (mut f32) (f32.const 0))
+
+  (func (export "get_one") (result f32) (global.get $one))
+  (func (export "get_some") (result f32) (global.get $some))
+
+  (func (export "set_some") (param f32) (global.set $some (local.get 0))))
+"#,
+    )?;
+
+    // Create a Store.
+    // Note that we don't need to specify the engine/compiler if we want to use
+    // the default provided by Wasmer.
+    // You can use `Store::default()` for that.
+    let store = Store::new(&JIT::new(&Cranelift::default()).engine());
+
+    println!("Compiling module...");
+    // Let's compile the Wasm module.
+    let module = Module::new(&store, wasm_bytes)?;
+
+    // Create an empty import object.
+    let import_object = imports! {};
+
+    println!("Instantiating module...");
+    // Let's instantiate the Wasm module.
+    let instance = Instance::new(&module, &import_object)?;
+
+    // Here we go.
+    //
+    // The Wasm module exports some globals. Let's get them.
+    // Note that
+    //
+    //     ```
+    //     get_global(name)
+    //     ```
+    //
+    // is just an alias to
+    //
+    //     ```
+    //     get::<Global>(name)`.
+    //     ```
+    let one = instance.exports.get_global("one")?;
+    let some = instance.exports.get_global("some")?;
+
+    println!("Getting global type informations...");
+    // Let's get the globals types. The results are `GlobalType`s.
+    let one_type = one.ty();
+    let some_type = some.ty();
+
+    println!("one type: {:?} {:?}", one_type.mutability, one_type.ty);
+    assert_eq!(one_type.mutability, Mutability::Const);
+    assert_eq!(one_type.ty, Type::F32);
+
+    println!("some type: {:?} {:?}", some_type.mutability, some_type.ty);
+    assert_eq!(some_type.mutability, Mutability::Var);
+    assert_eq!(some_type.ty, Type::F32);
+
+    println!("Getting global values...");
+    // Getting the values of globals can be done in two ways:
+    //   1. Through an exported function,
+    //   2. Using the Global API directly.
+    //
+    // We will use an exported function for the `one` global
+    // and the Global API for `some`.
+    let get_one = instance
+        .exports
+        .get_function("get_one")?
+        .native::<(), f32>()?;
+
+    let one_result = get_one.call()?;
+    let some_result = some.get();
+
+    println!("one value: {:?}", one_result);
+    assert_eq!(one_result, 1.0);
+
+    println!("some value: {:?}", some_result);
+    assert_eq!(some_result, Value::F32(0.0));
+
+    println!("Setting global values...");
+    // Trying to set the value of a immutable global (`const`)
+    // will result in a `RuntimeError`.
+    let result = one.set(Value::F32(42.0));
+    assert_eq!(
+        result.expect_err("Expected an error").message(),
+        "Attempted to set an immutable global"
+    );
+
+    let one_result = one.get();
+    println!("one value after `set`: {:?}", one_result);
+    assert_eq!(one_result, Value::F32(1.0));
+
+    // Setting the values of globals can be done in two ways:
+    //   1. Through an exported function,
+    //   2. Using the Global API directly.
+    //
+    // We will use both for the `some` global.
+    let set_some = instance
+        .exports
+        .get_function("set_some")?
+        .native::<f32, ()>()?;
+    set_some.call(21.0)?;
+    let some_result = some.get();
+    println!("some value after `set_some`: {:?}", some_result);
+    assert_eq!(some_result, Value::F32(21.0));
+
+    some.set(Value::F32(42.0))?;
+    let some_result = some.get();
+    println!("some value after `set`: {:?}", some_result);
+    assert_eq!(some_result, Value::F32(42.0));
+
+    Ok(())
+}
+
+#[test]
+fn test_exported_global() -> Result<(), Box<dyn std::error::Error>> {
+    main()
+}

examples/imports_global.rs

@@ -0,0 +1,120 @@
+//! A Wasm module can import entities, like functions, memories,
+//! globals and tables.
+//!
+//! This example illustrates how to use imported globals. They come
+//! in 2 flavors:
+//!
+//!   1. Immutable globals (const),
+//!   2. Mutable globals.
+//!
+//! You can run the example directly by executing in Wasmer root:
+//!
+//! ```shell
+//! cargo run --example imported-global --release --features "cranelift"
+//! ```
+//!
+//! Ready?
+
+use wasmer::{imports, wat2wasm, Global, Instance, Module, Store, Value};
+use wasmer_compiler_cranelift::Cranelift;
+use wasmer_engine_jit::JIT;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    // Let's declare the Wasm module with the text representation.
+    let wasm_bytes = wat2wasm(
+        br#"
+(module
+  (global $some (import "env" "some") f32)
+  (global $other (import "env" "other") (mut f32))
+
+  (func (export "get_some") (result f32) (global.get $some))
+  (func (export "get_other") (result f32) (global.get $other))
+
+  (func (export "set_other") (param f32) (global.set $other (local.get 0))))
+"#,
+    )?;
+
+    // Create a Store.
+    // Note that we don't need to specify the engine/compiler if we want to use
+    // the default provided by Wasmer.
+    // You can use `Store::default()` for that.
+    let store = Store::new(&JIT::new(&Cranelift::default()).engine());
+
+    println!("Compiling module...");
+    // Let's compile the Wasm module.
+    let module = Module::new(&store, wasm_bytes)?;
+
+    // Create the globals
+    let some = Global::new(&store, Value::F32(1.0));
+    let other = Global::new_mut(&store, Value::F32(2.0));
+
+    // Create an import object.
+    // We add the two required globals in the `env` namespace.
+    let import_object = imports! {
+        "env" => {
+            "some" => some.clone(),
+            "other" => other.clone(),
+        }
+    };
+
+    println!("Instantiating module...");
+    // Let's instantiate the Wasm module.
+    let instance = Instance::new(&module, &import_object)?;
+
+    // Here we go.
+    //
+    // The Wasm module only imports some globals. We'll have to interact
+    // with them either using the Global API or exported functions.
+    let get_some = instance
+        .exports
+        .get_function("get_some")?
+        .native::<(), f32>()?;
+    let get_other = instance
+        .exports
+        .get_function("get_other")?
+        .native::<(), f32>()?;
+
+    let some_result = get_some.call()?;
+    let other_result = get_other.call()?;
+
+    println!("some value (via `get_some`): {:?}", some_result);
+    println!("some value (via Global API): {:?}", some.get());
+    println!("other value (via `get_other`): {:?}", other_result);
+    println!("other value (via Global API): {:?}", other.get());
+
+    assert_eq!(some_result, some.get().f32().unwrap());
+    assert_eq!(other_result, other.get().f32().unwrap());
+
+    println!("Setting global values...");
+    // Trying to set the value of a immutable global (`const`)
+    // will result in a `RuntimeError`.
+    let result = some.set(Value::F32(42.0));
+    assert_eq!(
+        result.expect_err("Expected an error").message(),
+        "Attempted to set an immutable global"
+    );
+
+    other.set(Value::F32(21.0))?;
+    let other_result = other.get();
+    println!("other value after `set`: {:?}", other_result);
+    assert_eq!(other_result, Value::F32(21.0));
+
+    println!("Altering global values through exported functions...");
+    // Changes made to global through exported functions will
+    // be reflected on the host side.
+    let set_other = instance
+        .exports
+        .get_function("set_other")?
+        .native::<f32, ()>()?;
+    set_other.call(42.0)?;
+
+    println!("other value (via Global API): {:?}", other.get());
+    assert_eq!(other.get(), Value::F32(42.0));
+
+    Ok(())
+}
+
+#[test]
+fn test_imported_global() -> Result<(), Box<dyn std::error::Error>> {
+    main()
+}