Merge rayon-rs#673

673: Reduce the genericity of many closures r=nikomatsakis a=cuviper

The `take_while` closure only needs to be generic in `T`, along with a
captured `&AtomicBool`. When we write the closure directly, it carries
all the type baggage of `WhileSomeFolder<'f, C>::consumer_iter<I>`,
where the monomorphized type may explode. Instead, we can move this
closure to a standalone function for reduced genericity.

Co-authored-by: Josh Stone <cuviper@gmail.com>

Author: bors[bot]

rayon-core/src/job.rs

@@ -109,10 +109,14 @@ where
     R: Send,
 {
     unsafe fn execute(this: *const Self) {
+        fn call<R>(func: impl FnOnce(bool) -> R) -> impl FnOnce() -> R {
+            move || func(true)
+        }
+
         let this = &*this;
         let abort = unwind::AbortIfPanic;
         let func = (*this.func.get()).take().unwrap();
-        (*this.result.get()) = match unwind::halt_unwinding(|| func(true)) {
+        (*this.result.get()) = match unwind::halt_unwinding(call(func)) {
             Ok(x) => JobResult::Ok(x),
             Err(x) => JobResult::Panic(x),
         };

rayon-core/src/join/mod.rs

@@ -98,7 +98,12 @@ where
     RA: Send,
     RB: Send,
 {
-    join_context(|_| oper_a(), |_| oper_b())
+    #[inline]
+    fn call<R>(f: impl FnOnce() -> R) -> impl FnOnce(FnContext) -> R {
+        move |_| f()
+    }
+
+    join_context(call(oper_a), call(oper_b))
 }
 
 /// Identical to `join`, except that the closures have a parameter
@@ -115,22 +120,30 @@ where
     RA: Send,
     RB: Send,
 {
+    #[inline]
+    fn call_a<R>(f: impl FnOnce(FnContext) -> R, injected: bool) -> impl FnOnce() -> R {
+        move || f(FnContext::new(injected))
+    }
+
+    #[inline]
+    fn call_b<R>(f: impl FnOnce(FnContext) -> R) -> impl FnOnce(bool) -> R {
+        move |migrated| f(FnContext::new(migrated))
+    }
+
     registry::in_worker(|worker_thread, injected| unsafe {
         log!(Join {
             worker: worker_thread.index()
         });
 
-        let latch = SpinLatch::new();
-
         // Create virtual wrapper for task b; this all has to be
         // done here so that the stack frame can keep it all live
         // long enough.
-        let job_b = StackJob::new(|migrated| oper_b(FnContext::new(migrated)), latch);
+        let job_b = StackJob::new(call_b(oper_b), SpinLatch::new());
         let job_b_ref = job_b.as_job_ref();
         worker_thread.push(job_b_ref);
 
         // Execute task a; hopefully b gets stolen in the meantime.
-        let status_a = unwind::halt_unwinding(move || oper_a(FnContext::new(injected)));
+        let status_a = unwind::halt_unwinding(call_a(oper_a, injected));
         let result_a = match status_a {
             Ok(v) => v,
             Err(err) => join_recover_from_panic(worker_thread, &job_b.latch, err),

src/iter/collect/mod.rs

@@ -1,5 +1,4 @@
 use super::{IndexedParallelIterator, IntoParallelIterator, ParallelExtend, ParallelIterator};
-use std::collections::LinkedList;
 use std::slice;
 use std::sync::atomic::{AtomicUsize, Ordering};
 
@@ -138,24 +137,10 @@ where
             }
             None => {
                 // This works like `extend`, but `Vec::append` is more efficient.
-                let list: LinkedList<_> = par_iter
-                    .fold(Vec::new, |mut vec, elem| {
-                        vec.push(elem);
-                        vec
-                    })
-                    .map(|vec| {
-                        let mut list = LinkedList::new();
-                        list.push_back(vec);
-                        list
-                    })
-                    .reduce(LinkedList::new, |mut list1, mut list2| {
-                        list1.append(&mut list2);
-                        list1
-                    });
-
-                self.reserve(list.iter().map(Vec::len).sum());
-                for mut vec in list {
-                    self.append(&mut vec);
+                let list = super::extend::collect(par_iter);
+                self.reserve(super::extend::len(&list));
+                for ref mut vec in list {
+                    self.append(vec);
                 }
             }
         }

src/iter/copied.rs

@@ -102,11 +102,11 @@ where
     T: 'a + Copy,
 {
     type Item = T;
-    type IntoIter = iter::Map<P::IntoIter, fn(&T) -> T>;
+    type IntoIter = iter::Cloned<P::IntoIter>;
 
     fn into_iter(self) -> Self::IntoIter {
         // FIXME: use `Iterator::copied()` when Rust 1.36 is our minimum.
-        self.base.into_iter().map(|&x| x)
+        self.base.into_iter().cloned()
     }
 
     fn min_len(&self) -> usize {
@@ -211,7 +211,7 @@ where
         I: IntoIterator<Item = &'a T>,
     {
         // FIXME: use `Iterator::copied()` when Rust 1.36 is our minimum.
-        self.base = self.base.consume_iter(iter.into_iter().map(|&x| x));
+        self.base = self.base.consume_iter(iter.into_iter().cloned());
         self
     }