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Auto merge of #10582 - bholley:no_move_style_structs, r=Manishearth

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Avoid moves of Gecko style structs

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This commit is contained in:
bors-servo 2016-04-14 05:22:20 +05:30
commit 25ae04057c
2 changed files with 18 additions and 5 deletions
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1
ports/geckolib/lib.rs
View file

@ -5,6 +5,7 @@
#![feature(as_unsafe_cell)] #![feature(as_unsafe_cell)]
#![feature(box_syntax)] #![feature(box_syntax)]
#![feature(ptr_as_ref)] #![feature(ptr_as_ref)]
#![feature(custom_attribute)]
#![feature(custom_derive)] #![feature(custom_derive)]
#![feature(plugin)] #![feature(plugin)]

22
ports/geckolib/properties.mako.rs
View file

@ -96,6 +96,7 @@ impl ComputedValues for GeckoComputedValues {
<%def name="declare_style_struct(style_struct)"> <%def name="declare_style_struct(style_struct)">
#[derive(Clone, HeapSizeOf, Debug)] #[derive(Clone, HeapSizeOf, Debug)]
#[no_move]
% if style_struct.gecko_ffi_name: % if style_struct.gecko_ffi_name:
pub struct ${style_struct.gecko_struct_name} { pub struct ${style_struct.gecko_struct_name} {
gecko: ${style_struct.gecko_ffi_name}, gecko: ${style_struct.gecko_ffi_name},
@ -108,15 +109,26 @@ pub struct ${style_struct.gecko_struct_name};
<%def name="impl_style_struct(style_struct)"> <%def name="impl_style_struct(style_struct)">
impl ${style_struct.gecko_struct_name} { impl ${style_struct.gecko_struct_name} {
#[allow(dead_code, unused_variables)] #[allow(dead_code, unused_variables)]
fn initial() -> Self { fn initial() -> Arc<Self> {
% if style_struct.gecko_ffi_name: % if style_struct.gecko_ffi_name:
let mut result = ${style_struct.gecko_struct_name} { gecko: unsafe { zeroed() } }; // Some Gecko style structs have AutoTArray members, which have internal pointers and are
// thus MOZ_NON_MEMMOVABLE. Since Rust is generally a very move-happy language, we need to
// be very careful that nsStyle* structs are never moved after they are constructed.
//
// By annotating the structs [no_move], we can get the |rust-tenacious| linter to trigger
// an error on any semantic moves. But we don't have a great way of telling LLVM to
// allocate our new object directly on the heap without using a temporary. So to do that
// (and also please tenacious), we pass zeroed memory into the Arc constructor, and _then_
// use make_mut to get a reference to pass to the Gecko constructor. Since the refcount is
// guaranteed to be 1, make_mut will always pass us a direct reference instead of taking
// the copy-on-write path.
let mut result = Arc::new(${style_struct.gecko_struct_name} { gecko: unsafe { zeroed() } });
unsafe { unsafe {
Gecko_Construct_${style_struct.gecko_ffi_name}(&mut result.gecko); Gecko_Construct_${style_struct.gecko_ffi_name}(&mut Arc::make_mut(&mut result).gecko);
} }
result result
% else: % else:
${style_struct.gecko_struct_name} Arc::new(${style_struct.gecko_struct_name})
% endif % endif
} }
} }
@ -224,7 +236,7 @@ ${impl_style_struct(style_struct)}
lazy_static! { lazy_static! {
pub static ref INITIAL_GECKO_VALUES: GeckoComputedValues = GeckoComputedValues { pub static ref INITIAL_GECKO_VALUES: GeckoComputedValues = GeckoComputedValues {
% for style_struct in STYLE_STRUCTS: % for style_struct in STYLE_STRUCTS:
${style_struct.ident}: Arc::new(${style_struct.gecko_struct_name}::initial()), ${style_struct.ident}: ${style_struct.gecko_struct_name}::initial(),
% endfor % endfor
custom_properties: None, custom_properties: None,
shareable: true, shareable: true,