From bb1c30838054bffb5ba32ee09991222fdef08979 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lauren=C8=9Biu=20Nicola?= <lnicola@dend.ro>
Date: Sat, 27 Jun 2020 13:40:37 +0300
Subject: [PATCH] Revert "Bump parking_lot and remove workaround"

This reverts commit 025c882cbb1e252da56bf09d7e946fbed316bb54.
---
 Cargo.toml          |  3 +--
 src/derived/slot.rs | 15 +++++++--------
 2 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 34a0c05..27d2e24 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -11,9 +11,8 @@ readme = "README.md"
 [dependencies]
 crossbeam = "0.7.1"
 indexmap = "1.0.1"
-lock_api = "0.4"
 log = "0.4.5"
-parking_lot = "0.11.0"
+parking_lot = "0.10.0"
 rustc-hash = "1.0"
 smallvec = "1.0.0"
 rand = { version = "0.7", features = [ "small_rng" ] }
diff --git a/src/derived/slot.rs b/src/derived/slot.rs
index 43a4d08..83a2fd5 100644
--- a/src/derived/slot.rs
+++ b/src/derived/slot.rs
@@ -15,10 +15,9 @@ use crate::runtime::Runtime;
 use crate::runtime::RuntimeId;
 use crate::runtime::StampedValue;
 use crate::{CycleError, Database, DiscardIf, DiscardWhat, Event, EventKind, SweepStrategy};
-// use lock_api::RawRwLockUpgrade;
 use log::{debug, info};
 use parking_lot::Mutex;
-use parking_lot::{RawRwLock, RwLock};
+use parking_lot::RwLock;
 use smallvec::SmallVec;
 use std::marker::PhantomData;
 use std::ops::Deref;
@@ -166,13 +165,13 @@ where
         // Check with an upgradable read to see if there is a value
         // already. (This permits other readers but prevents anyone
         // else from running `read_upgrade` at the same time.)
-        let old_memo = match self.probe(db, self.state.upgradable_read(), runtime, revision_now) {
+        //
+        // FIXME(Amanieu/parking_lot#101) -- we are using a write-lock
+        // and not an upgradable read here because upgradable reads
+        // can sometimes encounter deadlocks.
+        let old_memo = match self.probe(db, self.state.write(), runtime, revision_now) {
             ProbeState::UpToDate(v) => return v,
-            ProbeState::StaleOrAbsent(state) => {
-                type RwLockUpgradableReadGuard<'a, T> =
-                    lock_api::RwLockUpgradableReadGuard<'a, RawRwLock, T>;
-
-                let mut state = RwLockUpgradableReadGuard::upgrade(state);
+            ProbeState::StaleOrAbsent(mut state) => {
                 match std::mem::replace(&mut *state, QueryState::in_progress(runtime.id())) {
                     QueryState::Memoized(old_memo) => Some(old_memo),
                     QueryState::InProgress { .. } => unreachable!(),