Use std sync primitives instead of parking_lot

[BratSinot]

Greetings!

Since 1.62 rust start to use sync primitives based on futex (unstead of pthreads) in */Linux systems and it become equal (or faster in some cases) by speed with parking_lot.

We can save "poison" behaviour from parking_lot by this:

    use std::sync::{PoisonError, RwLockReadGuard, RwLockWriteGuard};

    pub(crate) struct RwLock<T>(std::sync::RwLock<T>);

    impl<T> RwLock<T> {
        #[inline]
        pub(crate) fn new(t: T) -> Self {
            Self(std::sync::RwLock::new(t))
        }

        #[inline]
        pub(crate) fn read(&self) -> RwLockReadGuard<T> {
            self.0.read().unwrap_or_else(PoisonError::into_inner)
        }

        #[inline]
        pub(crate) fn write(&self) -> RwLockWriteGuard<T> {
            self.0.write().unwrap_or_else(PoisonError::into_inner)
        }
    }

But the problem is that minimal rust version in yours crates is 1.56.1 and if someone use older compiler version speed will degradate.
In some crates I can add parking_lot as optional:

diff --git a/metrics-exporter-prometheus/Cargo.toml b/metrics-exporter-prometheus/Cargo.toml
index e24aaf2..e6160ea 100644
--- a/metrics-exporter-prometheus/Cargo.toml
+++ b/metrics-exporter-prometheus/Cargo.toml
@@ -17,7 +17,7 @@ categories = ["development-tools::debugging"]
 keywords = ["metrics", "telemetry", "prometheus"]
 
 [features]
-default = ["http-listener", "push-gateway"]
+default = ["http-listener", "push-gateway", "parking_lot"]
 async-runtime = ["tokio", "hyper"]
 http-listener = ["async-runtime", "hyper/server", "ipnet"]
 push-gateway = ["async-runtime", "hyper/client", "tracing"]
@@ -25,7 +25,7 @@ push-gateway = ["async-runtime", "hyper/client", "tracing"]
 [dependencies]
 metrics = { version = "^0.20", path = "../metrics" }
 metrics-util = { version = "^0.14", path = "../metrics-util", default-features = false, features = ["recency", "registry", "summary"] }
-parking_lot = { version = "0.12", default-features = false }
+parking_lot = { version = "0.12", optional = true, default-features = false }
 thiserror = { version = "1", default-features = false }
 quanta = { version = "0.10.0", default-features = false }
 indexmap = { version = "1", default-features = false }
diff --git a/metrics-exporter-prometheus/src/builder.rs b/metrics-exporter-prometheus/src/builder.rs
index 2e5bd6c..2db688a 100644
--- a/metrics-exporter-prometheus/src/builder.rs
+++ b/metrics-exporter-prometheus/src/builder.rs
@@ -31,7 +31,6 @@ use hyper::{
 use indexmap::IndexMap;
 #[cfg(feature = "http-listener")]
 use ipnet::IpNet;
-use parking_lot::RwLock;
 use quanta::Clock;
 #[cfg(any(feature = "http-listener", feature = "push-gateway"))]
 use tokio::runtime;
@@ -48,6 +47,7 @@ use crate::common::Matcher;
 use crate::distribution::DistributionBuilder;
 use crate::recorder::{Inner, PrometheusRecorder};
 use crate::registry::AtomicStorage;
+use crate::sync::RwLock;
 use crate::{common::BuildError, PrometheusHandle};
 
 #[cfg(any(feature = "http-listener", feature = "push-gateway"))]
@@ -480,7 +480,7 @@ impl PrometheusBuilder {
                                     let body = body
                                         .map_err(|_| ())
                                         .map(|mut b| b.copy_to_bytes(b.remaining()))
-                                        .map(|b| (&b[..]).to_vec())
+                                        .map(|b| (b[..]).to_vec())
                                         .and_then(|s| String::from_utf8(s).map_err(|_| ()))
                                         .unwrap_or_else(|_| {
                                             String::from("<failed to read response body>")
diff --git a/metrics-exporter-prometheus/src/lib.rs b/metrics-exporter-prometheus/src/lib.rs
index 399d942..e19dcd9 100644
--- a/metrics-exporter-prometheus/src/lib.rs
+++ b/metrics-exporter-prometheus/src/lib.rs
@@ -113,5 +113,6 @@ pub mod formatting;
 mod recorder;
 
 mod registry;
+mod sync;
 
 pub use self::recorder::{PrometheusHandle, PrometheusRecorder};
diff --git a/metrics-exporter-prometheus/src/recorder.rs b/metrics-exporter-prometheus/src/recorder.rs
index 6d746df..223969b 100644
--- a/metrics-exporter-prometheus/src/recorder.rs
+++ b/metrics-exporter-prometheus/src/recorder.rs
@@ -5,7 +5,6 @@ use std::sync::Arc;
 use indexmap::IndexMap;
 use metrics::{Counter, Gauge, Histogram, Key, KeyName, Recorder, SharedString, Unit};
 use metrics_util::registry::{Recency, Registry};
-use parking_lot::RwLock;
 use quanta::Instant;
 
 use crate::common::Snapshot;
@@ -14,6 +13,7 @@ use crate::formatting::{
     key_to_parts, sanitize_metric_name, write_help_line, write_metric_line, write_type_line,
 };
 use crate::registry::GenerationalAtomicStorage;
+use crate::sync::RwLock;
 
 pub(crate) struct Inner {
     pub registry: Registry<Key, GenerationalAtomicStorage>,
diff --git a/metrics-exporter-prometheus/src/sync.rs b/metrics-exporter-prometheus/src/sync.rs
index e69de29..dfb3b8d 100644
--- a/metrics-exporter-prometheus/src/sync.rs
+++ b/metrics-exporter-prometheus/src/sync.rs
@@ -0,0 +1,29 @@
+#[cfg(feature = "parking_lot")]
+pub(crate) use parking_lot::RwLock;
+
+#[cfg(not(feature = "parking_lot"))]
+mod std_mutex {
+    use std::sync::{PoisonError, RwLockReadGuard, RwLockWriteGuard};
+
+    pub(crate) struct RwLock<T>(std::sync::RwLock<T>);
+
+    impl<T> RwLock<T> {
+        #[inline]
+        pub(crate) fn new(t: T) -> Self {
+            Self(std::sync::RwLock::new(t))
+        }
+
+        #[inline]
+        pub(crate) fn read(&self) -> RwLockReadGuard<T> {
+            self.0.read().unwrap_or_else(PoisonError::into_inner)
+        }
+
+        #[inline]
+        pub(crate) fn write(&self) -> RwLockWriteGuard<T> {
+            self.0.write().unwrap_or_else(PoisonError::into_inner)
+        }
+    }
+}
+
+#[cfg(not(feature = "parking_lot"))]
+pub(crate) use std_mutex::*;

But in some crates it already optional hidden by different flag, like in metrics-util:

recency = ["parking_lot", "registry", "quanta"]

and I can't make usage of std sync primitive by flag and save old behaviour.

I see only 3 ways:

1. remove parking_lot deps;
2. use std sync primitives by default and make usage of parking_lot optional;
3. doesn't bore at all and continue to use parking_lot;

But I want to remove extra deps and option 3 isn't acceptable personally for me =)

Any thoughts on this case?

[tobz]

@BratSinot I'd be OK with removing the parking_lot dependency entirely.

I mostly only ever used it because I disliked the additional result handling introduced by handling poisoned lock errors... but it's probably worth just adding a wrapper like you suggested (or something else) and using the stdlib version to reduce the number of dependencies, especially given the idea of pushing towards 1.0.