fallible: Avoid using system malloc in servo.

components/fallible/Cargo.toml

@@ -12,3 +12,14 @@ path = "lib.rs"
 [dependencies]
 smallvec = "0.4"
 hashglobe = { path = "../hashglobe" }
+
+# This crate effectively does nothing except if the `known_system_malloc`
+# feature is specified.
+#
+# In that case, we actually call the system malloc functions to reserve space,
+# otherwise we just let rust do its thing (aborting on OOM).
+#
+# This is effectively a stop-gap measure until we can do this properly in
+# stable rust.
+[features]
+known_system_malloc = []

components/fallible/lib.rs

@@ -8,10 +8,9 @@ extern crate smallvec;
 use hashglobe::FailedAllocationError;
 use smallvec::Array;
 use smallvec::SmallVec;
-use std::mem;
-use std::ptr::copy_nonoverlapping;
 use std::vec::Vec;
 
+#[cfg(feature = "known_system_malloc")]
 extern "C" {
     fn realloc(ptr: *mut u8, bytes: usize) -> *mut u8;
     fn malloc(bytes: usize) -> *mut u8;
@@ -30,10 +29,13 @@ pub trait FallibleVec<T> {
 impl<T> FallibleVec<T> for Vec<T> {
     #[inline]
     fn try_push(&mut self, val: T) -> Result<(), FailedAllocationError> {
+        #[cfg(feature = "known_system_malloc")]
+        {
             if self.capacity() == self.len() {
                 try_double_vec(self)?;
                 debug_assert!(self.capacity() > self.len());
             }
+        }
         self.push(val);
         Ok(())
     }
@@ -41,9 +43,12 @@ impl<T> FallibleVec<T> for Vec<T> {
 
 // Double the capacity of |vec|, or fail to do so due to lack of memory.
 // Returns Ok(()) on success, Err(..) on failure.
+#[cfg(feature = "known_system_malloc")]
 #[inline(never)]
 #[cold]
 fn try_double_vec<T>(vec: &mut Vec<T>) -> Result<(), FailedAllocationError> {
+    use std::mem;
+
     let old_ptr = vec.as_mut_ptr();
     let old_len = vec.len();
 
@@ -89,10 +94,13 @@ fn try_double_vec<T>(vec: &mut Vec<T>) -> Result<(), FailedAllocationError> {
 impl<T: Array> FallibleVec<T::Item> for SmallVec<T> {
     #[inline]
     fn try_push(&mut self, val: T::Item) -> Result<(), FailedAllocationError> {
+        #[cfg(feature = "known_system_malloc")]
+        {
             if self.capacity() == self.len() {
                 try_double_small_vec(self)?;
                 debug_assert!(self.capacity() > self.len());
             }
+        }
         self.push(val);
         Ok(())
     }
@@ -100,6 +108,7 @@ impl<T: Array> FallibleVec<T::Item> for SmallVec<T> {
 
 // Double the capacity of |svec|, or fail to do so due to lack of memory.
 // Returns Ok(()) on success, Err(..) on failure.
+#[cfg(feature = "known_system_malloc")]
 #[inline(never)]
 #[cold]
 fn try_double_small_vec<T>(svec: &mut SmallVec<T>)
@@ -107,6 +116,9 @@ fn try_double_small_vec<T>(svec: &mut SmallVec<T>)
 where
     T: Array,
 {
+    use std::mem;
+    use std::ptr::copy_nonoverlapping;
+
     let old_ptr = svec.as_mut_ptr();
     let old_len = svec.len();
 

components/style/Cargo.toml

@@ -16,7 +16,7 @@ path = "lib.rs"
 doctest = false
 
 [features]
-gecko = ["nsstring_vendor", "num_cpus", "style_traits/gecko"]
+gecko = ["nsstring_vendor", "num_cpus", "style_traits/gecko", "fallible/known_system_malloc"]
 use_bindgen = ["bindgen", "regex", "toml"]
 servo = ["serde", "heapsize", "heapsize_derive",
          "style_traits/servo", "servo_atoms", "servo_config", "html5ever",