---

yaml
---
r: 73462
b: refs/heads/dist-snap
c: dea6677
h: refs/heads/master
v: v3

Author: Olivier Saut

[refs]

@@ -7,7 +7,7 @@ refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
 refs/heads/try2: 147ecfdd8221e4a4d4e090486829a06da1e0ca3c
 refs/heads/incoming: b50030718cf28f2a5a81857a26b57442734fe854
-refs/heads/dist-snap: 1f8c4b096da8d7c6436038730fa4a862e1ac91f5
+refs/heads/dist-snap: dea667725137368dd9c928bae3c091b9ccf42e67
 refs/tags/release-0.2: c870d2dffb391e14efb05aa27898f1f6333a9596
 refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503
 refs/heads/try3: 9387340aab40a73e8424c48fd42f0c521a4875c0

branches/dist-snap/doc/tutorial-tasks.md

@@ -284,7 +284,7 @@ let result = ports.foldl(0, |accum, port| *accum + port.recv() );
 # fn some_expensive_computation(_i: uint) -> int { 42 }
 ~~~
 
-## Futures
+## Backgrounding computations: Futures
 With `extra::future`, rust has a mechanism for requesting a computation and getting the result
 later.
 
@@ -329,6 +329,77 @@ fn main() {
 }
 ~~~
 
+## Sharing immutable data without copy: ARC
+
+To share immutable data between tasks, a first approach would be to only use pipes as we have seen
+previously. A copy of the data to share would then be made for each task. In some cases, this would
+add up to a significant amount of wasted memory and would require copying the same data more than
+necessary.
+
+To tackle this issue, one can use an Atomically Reference Counted wrapper (`ARC`) as implemented in
+the `extra` library of Rust. With an ARC, the data will no longer be copied for each task. The ARC
+acts as a reference to the shared data and only this reference is shared and cloned.
+
+Here is a small example showing how to use ARCs. We wish to run concurrently several computations on
+a single large vector of floats. Each task needs the full vector to perform its duty.
+~~~
+use extra::arc::ARC;
+
+fn pnorm(nums: &~[float], p: uint) -> float {
+    (vec::foldl(0.0, *nums, |a,b| a+(*b).pow(p as float) )).pow(1f / (p as float))
+}
+
+fn main() {
+    let numbers=vec::from_fn(1000000, |_| rand::random::<float>());
+    println(fmt!("Inf-norm = %?",  numbers.max()));
+
+    let numbers_arc = ARC(numbers);
+
+    for uint::range(1,10) |num| {
+        let (port, chan)  = stream();
+        chan.send(numbers_arc.clone());
+
+        do spawn {
+            let local_arc : ARC<~[float]> = port.recv();
+            let task_numbers = local_arc.get();
+            println(fmt!("%u-norm = %?", num, pnorm(task_numbers, num)));
+        }
+    }
+}
+~~~
+
+The function `pnorm` performs a simple computation on the vector (it computes the sum of its items
+at the power given as argument and takes the inverse power of this value). The ARC on the vector is
+created by the line
+~~~
+# use extra::arc::ARC;
+# let numbers=vec::from_fn(1000000, |_| rand::random::<float>());
+let numbers_arc=ARC(numbers);
+~~~
+and a clone of it is sent to each task
+~~~
+# use extra::arc::ARC;
+# let numbers=vec::from_fn(1000000, |_| rand::random::<float>());
+# let numbers_arc = ARC(numbers);
+# let (port, chan)  = stream();
+chan.send(numbers_arc.clone());
+~~~
+copying only the wrapper and not its contents.
+
+Each task recovers the underlying data by
+~~~
+# use extra::arc::ARC;
+# let numbers=vec::from_fn(1000000, |_| rand::random::<float>());
+# let numbers_arc=ARC(numbers);
+# let (port, chan)  = stream();
+# chan.send(numbers_arc.clone());
+# let local_arc : ARC<~[float]> = port.recv();
+let task_numbers = local_arc.get();
+~~~
+and can use it as if it were local.
+
+The `arc` module also implements ARCs around mutable data that are not covered here.
+
 # Handling task failure
 
 Rust has a built-in mechanism for raising exceptions. The `fail!()` macro

branches/dist-snap/src/librustc/middle/trans/base.rs

@@ -1694,20 +1694,7 @@ pub fn create_llargs_for_fn_args(cx: fn_ctxt,
     vec::from_fn(args.len(), |i| {
         unsafe {
             let arg_n = first_real_arg + i;
-            let arg = &args[i];
-            let llarg = llvm::LLVMGetParam(cx.llfn, arg_n as c_uint);
-
-            // Mark `&mut T` as no-alias, as the borrowck pass ensures it's true
-            match arg.ty.node {
-                ast::ty_rptr(_, mt) => {
-                    if mt.mutbl == ast::m_mutbl  {
-                        llvm::LLVMAddAttribute(llarg, lib::llvm::NoAliasAttribute as c_uint);
-                    }
-                }
-                _ => {}
-            }
-
-            llarg
+            llvm::LLVMGetParam(cx.llfn, arg_n as c_uint)
         }
     })
 }

branches/dist-snap/src/librustdoc/markdown_pass.rs

@@ -451,32 +451,16 @@ fn write_variants(
 fn write_variant(ctxt: &Ctxt, doc: doc::VariantDoc) {
     assert!(doc.sig.is_some());
     let sig = (&doc.sig).get();
-
-    // space out list items so they all end up within paragraph elements
-    ctxt.w.put_line(~"");
-
     match copy doc.desc {
         Some(desc) => {
-            ctxt.w.put_line(list_item_indent(fmt!("* `%s` - %s", sig, desc)));
+            ctxt.w.put_line(fmt!("* `%s` - %s", sig, desc));
         }
         None => {
             ctxt.w.put_line(fmt!("* `%s`", sig));
         }
     }
 }
 
-fn list_item_indent(item: &str) -> ~str {
-    let mut indented = ~[];
-    for str::each_line_any(item) |line| {
-        indented.push(line);
-    }
-
-    // separate markdown elements within `*` lists must be indented by four
-    // spaces, or they will escape the list context. indenting everything
-    // seems fine though.
-    str::connect_slices(indented, "\n    ")
-}
-
 fn write_trait(ctxt: &Ctxt, doc: doc::TraitDoc) {
     write_common(ctxt, doc.desc(), doc.sections());
     write_methods(ctxt, doc.methods);
@@ -823,9 +807,7 @@ mod test {
         assert!(str::contains(
             markdown,
             "\n\n#### Variants\n\
-             \n\
              \n* `b` - test\
-             \n\
              \n* `c` - test\n\n"));
     }
 
@@ -835,24 +817,7 @@ mod test {
         assert!(str::contains(
             markdown,
             "\n\n#### Variants\n\
-             \n\
              \n* `b`\
-             \n\
-             \n* `c`\n\n"));
-    }
-
-    #[test]
-    fn should_write_variant_list_with_indent() {
-        let markdown = render(
-            ~"enum a { #[doc = \"line 1\\n\\nline 2\"] b, c }");
-        assert!(str::contains(
-            markdown,
-            "\n\n#### Variants\n\
-             \n\
-             \n* `b` - line 1\
-             \n    \
-             \n    line 2\
-             \n\
              \n* `c`\n\n"));
     }
 
@@ -862,9 +827,7 @@ mod test {
         assert!(str::contains(
             markdown,
             "\n\n#### Variants\n\
-             \n\
              \n* `b(int)`\
-             \n\
              \n* `c(int)` - a\n\n"));
     }