epoch: Make loom able to test treiber stack

With this change, loom runs to completion on the treiber test!
I ran it with `LOOM_MAX_PREEMPTIONS=3`, and it took _forever_ (well, it
took 2h), but eventually finished with:

     ================== Iteration 112280000 ==================

    Completed in 112291514 iterations
    ok

With `LOOM_MAX_PREEMPTIONS=2` it "only" took 13 minutes, and finished
with:

     ================== Iteration 9680000 ==================

    Completed in 9690926 iterations
    ok

I updated the CI script to run with `LOOM_MAX_PREEMPTIONS=2`.

Note that this change depends on
tokio-rs/loom#125 and
tokio-rs/loom#128. The `patch` in the root
`Cargo.toml` should be removed once a new loom release is made.

Cargo.toml

@@ -74,3 +74,6 @@ members = [
   "crossbeam-skiplist",
   "crossbeam-utils",
 ]
+
+[patch.crates-io]
+loom = { git = "https://github.com/jonhoo/loom.git", branch = "lazy_static-race" }

ci/crossbeam-epoch-loom.sh

@@ -5,4 +5,4 @@ set -ex
 
 export RUSTFLAGS="-D warnings"
 
-env LOOM_MAX_PREEMPTIONS=3 cargo test --test loom --features with-loom --release -- --nocapture
+env LOOM_MAX_PREEMPTIONS=2 cargo test --test loom --features with-loom --release -- --nocapture

crossbeam-epoch/src/default.rs

@@ -7,7 +7,7 @@
 use collector::{Collector, LocalHandle};
 use guard::Guard;
 
-lazy_static! {
+::concurrency::lazy_static! {
     /// The global data for the default garbage collector.
     static ref COLLECTOR: Collector = Collector::new();
 }

crossbeam-epoch/src/lib.rs

@@ -92,6 +92,12 @@ pub(crate) mod concurrency {
         pub(crate) use loom::sync::Arc;
     }
     pub(crate) use loom::thread_local;
+
+    cfg_if! {
+        if #[cfg(feature = "std")] {
+            pub(crate) use loom::lazy_static;
+        }
+    }
 }
 #[cfg(not(feature = "with-loom"))]
 pub(crate) mod concurrency {
@@ -126,6 +132,13 @@ pub(crate) mod concurrency {
         pub(crate) use alloc::sync::Arc;
     }
     pub(crate) use std::thread_local;
+    pub(crate) use std::thread_local;
+
+    cfg_if! {
+        if #[cfg(feature = "std")] {
+            pub(crate) use lazy_static::lazy_static;
+        }
+    }
 }
 
 cfg_if! {
@@ -161,7 +174,6 @@ cfg_if! {
 
 cfg_if! {
     if #[cfg(feature = "std")] {
-        #[macro_use]
         extern crate lazy_static;
 
         mod default;

crossbeam-epoch/tests/loom.rs

@@ -127,14 +127,15 @@ fn treiber_stack() {
         let stack1 = Arc::new(TreiberStack::new());
         let stack2 = Arc::clone(&stack1);
 
+        // use 5 since it's greater than the 4 used for the sanitize feature
         let jh = spawn(move || {
-            for i in 0..20 {
+            for i in 0..5 {
                 stack2.push(i);
                 assert!(stack2.pop().is_some());
             }
         });
 
-        for i in 0..20 {
+        for i in 0..5 {
             stack1.push(i);
             assert!(stack1.pop().is_some());
         }