Stop relying on linking details of std’s default allocator

We’ve been bitten before by symbol names changing:
servo/heapsize#46
and upstream is planning to stop using jemalloc by default:
rust-lang/rust#33082 (comment)

So use the (relatively) new `#[global_allocator]` attribute
to explicitly select the system allocator on Windows
and jemalloc (now in an external crate) on other platforms.
This choice matches current defaults.

components/allocator/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "servo_allocator"
+version = "0.0.1"
+authors = ["The Servo Project Developers"]
+license = "MPL-2.0"
+publish = false
+
+[lib]
+path = "lib.rs"
+
+[features]
+unstable = ["kernel32-sys", "jemallocator"]
+
+[target.'cfg(not(windows))'.dependencies]
+jemallocator = { version = "0.1.3", optional = true }
+
+[target.'cfg(windows)'.dependencies]
+kernel32-sys = { version = "0.2.1", optional = true }

components/allocator/lib.rs

@@ -0,0 +1,61 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Selecting the default global allocator for Servo
+
+#![cfg_attr(feature = "unstable", feature(global_allocator))]
+
+#[cfg(feature = "unstable")]
+#[global_allocator]
+static ALLOC: platform::Allocator = platform::Allocator;
+
+pub use platform::usable_size;
+
+
+#[cfg(all(feature = "unstable", not(windows)))]
+mod platform {
+    extern crate jemallocator;
+
+    pub use self::jemallocator::Jemalloc as Allocator;
+    use std::os::raw::c_void;
+
+    /// Get the size of a heap block.
+    pub unsafe extern "C" fn usable_size(ptr: *const c_void) -> usize {
+        jemallocator::usable_size(ptr)
+    }
+}
+
+#[cfg(all(feature = "unstable", windows))]
+mod platform {
+    extern crate alloc_system;
+    extern crate kernel32;
+
+    pub use self::alloc_system::System as Allocator;
+    use self::kernel32::{GetProcessHeap, HeapSize, HeapValidate};
+    use std::os::raw::c_void;
+
+    /// Get the size of a heap block.
+    pub unsafe extern "C" fn malloc_size_of(mut ptr: *const c_void) -> usize {
+        let heap = GetProcessHeap();
+
+        if HeapValidate(heap, 0, ptr) == 0 {
+            ptr = *(ptr as *const *const c_void).offset(-1);
+        }
+
+        HeapSize(heap, 0, ptr) as usize
+    }
+}
+
+#[cfg(not(feature = "unstable"))]
+mod platform {
+    use std::os::raw::c_void;
+
+    /// Without `#[global_allocator]` we cannot be certain of what allocator is used
+    /// or how it is linked. We therefore disable memory reporting. (Return zero.)
+    pub unsafe extern "C" fn usable_size(_ptr: *const c_void) -> usize {
+        0
+    }
+}
+
+

components/gfx/Cargo.toml

@@ -53,6 +53,7 @@ core-text = "7.0"
 
 [target.'cfg(any(target_os = "linux", target_os = "android"))'.dependencies]
 freetype = "0.3"
+servo_allocator = {path = "../allocator"}
 
 [target.'cfg(target_os = "linux")'.dependencies]
 servo-fontconfig = "0.2.1"

components/gfx/lib.rs

@@ -27,8 +27,8 @@ extern crate fnv;
 #[cfg(target_os = "linux")]
 extern crate fontconfig;
 extern crate fontsan;
-#[cfg(any(target_os = "linux", target_os = "android"))]
-extern crate freetype;
+#[cfg(any(target_os = "linux", target_os = "android"))] extern crate freetype;
+#[cfg(any(target_os = "linux", target_os = "android"))] extern crate servo_allocator;
 extern crate gfx_traits;
 
 // Eventually we would like the shaper to be pluggable, as many operating systems have their own

components/gfx/platform/freetype/font_context.rs

@@ -8,7 +8,8 @@ use freetype::freetype::FT_Library;
 use freetype::freetype::FT_Memory;
 use freetype::freetype::FT_MemoryRec_;
 use freetype::freetype::FT_New_Library;
-use malloc_size_of::{malloc_size_of, MallocSizeOf, MallocSizeOfOps};
+use malloc_size_of::{MallocSizeOf, MallocSizeOfOps};
+use servo_allocator::usable_size;
 use std::mem;
 use std::os::raw::{c_long, c_void};
 use std::ptr;
@@ -31,7 +32,7 @@ extern fn ft_alloc(mem: FT_Memory, req_size: c_long) -> *mut c_void {
     mem::forget(vec);
 
     unsafe {
-        let actual_size = malloc_size_of(ptr as *const _);
+        let actual_size = usable_size(ptr as *const _);
         let user = (*mem).user as *mut User;
         (*user).size += actual_size;
     }
@@ -41,7 +42,7 @@ extern fn ft_alloc(mem: FT_Memory, req_size: c_long) -> *mut c_void {
 
 extern fn ft_free(mem: FT_Memory, ptr: *mut c_void) {
     unsafe {
-        let actual_size = malloc_size_of(ptr as *const _);
+        let actual_size = usable_size(ptr as *const _);
         let user = (*mem).user as *mut User;
         (*user).size -= actual_size;
 
@@ -50,13 +51,14 @@ extern fn ft_free(mem: FT_Memory, ptr: *mut c_void) {
     }
 }
 
-extern fn ft_realloc(mem: FT_Memory, _cur_size: c_long, new_req_size: c_long,
+extern fn ft_realloc(mem: FT_Memory, old_size: c_long, new_req_size: c_long,
                      old_ptr: *mut c_void) -> *mut c_void {
     let old_actual_size;
     let mut vec;
     unsafe {
-        old_actual_size = malloc_size_of(old_ptr as *const _);
-        vec = Vec::<u8>::from_raw_parts(old_ptr as *mut u8, old_actual_size, old_actual_size);
+        old_actual_size = usable_size(old_ptr as *const _);
+        let old_size = old_size as usize;
+        vec = Vec::<u8>::from_raw_parts(old_ptr as *mut u8, old_size, old_size);
     };
 
     let new_req_size = new_req_size as usize;
@@ -71,7 +73,7 @@ extern fn ft_realloc(mem: FT_Memory, _cur_size: c_long, new_req_size: c_long,
     mem::forget(vec);
 
     unsafe {
-        let new_actual_size = malloc_size_of(new_ptr as *const _);
+        let new_actual_size = usable_size(new_ptr as *const _);
         let user = (*mem).user as *mut User;
         (*user).size += new_actual_size;
         (*user).size -= old_actual_size;

components/layout_thread/Cargo.toml

@@ -40,6 +40,7 @@ script_layout_interface = {path = "../script_layout_interface"}
 script_traits = {path = "../script_traits"}
 selectors = { path = "../selectors" }
 serde_json = "1.0"
+servo_allocator = {path = "../allocator"}
 servo_arc = {path = "../servo_arc"}
 servo_atoms = {path = "../atoms"}
 servo_config = {path = "../config"}

components/layout_thread/lib.rs

@@ -39,6 +39,7 @@ extern crate script_layout_interface;
 extern crate script_traits;
 extern crate selectors;
 extern crate serde_json;
+extern crate servo_allocator;
 extern crate servo_arc;
 extern crate servo_atoms;
 extern crate servo_config;
@@ -84,7 +85,7 @@ use layout::webrender_helpers::WebRenderDisplayListConverter;
 use layout::wrapper::LayoutNodeLayoutData;
 use layout_traits::LayoutThreadFactory;
 use libc::c_void;
-use malloc_size_of::{malloc_size_of, MallocSizeOf, MallocSizeOfOps};
+use malloc_size_of::{MallocSizeOf, MallocSizeOfOps};
 use metrics::{PaintTimeMetrics, ProfilerMetadataFactory};
 use msg::constellation_msg::PipelineId;
 use msg::constellation_msg::TopLevelBrowsingContextId;
@@ -775,7 +776,7 @@ impl LayoutThread {
         let mut reports = vec![];
         // Servo uses vanilla jemalloc, which doesn't have a
         // malloc_enclosing_size_of function.
-        let mut ops = MallocSizeOfOps::new(malloc_size_of, None, None);
+        let mut ops = MallocSizeOfOps::new(::servo_allocator::usable_size, None, None);
 
         // FIXME(njn): Just measuring the display tree for now.
         let rw_data = possibly_locked_rw_data.lock();

components/malloc_size_of/Cargo.toml

@@ -8,9 +8,6 @@ publish = false
 [lib]
 path = "lib.rs"
 
-[target.'cfg(windows)'.dependencies]
-kernel32-sys = "0.2.1"
-
 [features]
 servo = ["js", "string_cache", "url", "webrender_api", "xml5ever"]
 

components/malloc_size_of/lib.rs

@@ -49,8 +49,6 @@ extern crate euclid;
 extern crate hashglobe;
 #[cfg(feature = "servo")]
 extern crate js;
-#[cfg(target_os = "windows")]
-extern crate kernel32;
 extern crate servo_arc;
 extern crate smallbitvec;
 extern crate smallvec;
@@ -63,8 +61,6 @@ extern crate webrender_api;
 #[cfg(feature = "servo")]
 extern crate xml5ever;
 
-#[cfg(target_os = "windows")]
-use kernel32::{GetProcessHeap, HeapSize, HeapValidate};
 use std::hash::{BuildHasher, Hash};
 use std::mem::size_of;
 use std::ops::Range;
@@ -146,33 +142,6 @@ impl MallocSizeOfOps {
     }
 }
 
-/// Get the size of a heap block.
-#[cfg(not(target_os = "windows"))]
-pub unsafe extern "C" fn malloc_size_of(ptr: *const c_void) -> usize {
-    // The C prototype is `je_malloc_usable_size(JEMALLOC_USABLE_SIZE_CONST void *ptr)`. On some
-    // platforms `JEMALLOC_USABLE_SIZE_CONST` is `const` and on some it is empty. But in practice
-    // this function doesn't modify the contents of the block that `ptr` points to, so we use
-    // `*const c_void` here.
-    extern "C" {
-        #[cfg_attr(any(prefixed_jemalloc, target_os = "macos", target_os = "ios", target_os = "android"),
-                   link_name = "je_malloc_usable_size")]
-        fn malloc_usable_size(ptr: *const c_void) -> usize;
-    }
-    malloc_usable_size(ptr)
-}
-
-/// Get the size of a heap block.
-#[cfg(target_os = "windows")]
-pub unsafe extern "C" fn malloc_size_of(mut ptr: *const c_void) -> usize {
-    let heap = GetProcessHeap();
-
-    if HeapValidate(heap, 0, ptr) == 0 {
-        ptr = *(ptr as *const *const c_void).offset(-1);
-    }
-
-    HeapSize(heap, 0, ptr) as usize
-}
-
 /// Trait for measuring the "deep" heap usage of a data structure. This is the
 /// most commonly-used of the traits.
 pub trait MallocSizeOf {

components/profile/Cargo.toml

@@ -10,7 +10,7 @@ name = "profile"
 path = "lib.rs"
 
 [features]
-unstable = []
+unstable = ["jemalloc-sys"]
 
 [dependencies]
 profile_traits = {path = "../profile_traits"}
@@ -31,3 +31,4 @@ regex = "0.2"
 
 [target.'cfg(not(target_os = "windows"))'.dependencies]
 libc = "0.2"
+jemalloc-sys = {version = "0.1.3", optional = true}