Adds tracing feature flag for deadpool-sync and sqlite. (#238)

With deadpool-sqlite, the database interactions happen in a sync context
(due to using rusqlite) on a separate thread. The tracing crate can add
conetxt to any logs (events). Due to the database interactions happening
on a separate thread, this context gets lost. Enabling the tracing
feature allows the information to be preserved.

Related: dbrgn/tracing-test#23

Note: I don't know if this is something that should rather be
implemented in the `spawn_blocking` method of Tokio.

sqlite/Cargo.toml

@@ -19,6 +19,7 @@ default = ["rt_tokio_1"]
 rt_tokio_1 = ["deadpool/rt_tokio_1"]
 rt_async-std_1 = ["deadpool/rt_async-std_1"]
 serde = ["deadpool/serde", "serde_1"]
+tracing = ["deadpool-sync/tracing"]
 
 [dependencies]
 deadpool = { path = "../", version = "0.10.0", default-features = false, features = [

sqlite/README.md

@@ -15,6 +15,7 @@ inside a separate thread.
 | `rt_tokio_1` | Enable support for [tokio](https://crates.io/crates/tokio) crate | `deadpool/rt_tokio_1` | yes |
 | `rt_async-std_1` | Enable support for [async-std](https://crates.io/crates/config) crate | `deadpool/rt_async-std_1` | no |
 | `serde` | Enable support for [serde](https://crates.io/crates/serde) crate | `deadpool/serde`, `serde/derive` | no |
+| `tracing` | Enable support for [tracing](https://github.com/tokio-rs/tracing) by propagating Spans in the `interact()` calls. Enable this if you use the `tracing` crate and you want to get useful traces from within `interact()` calls. | `tracing` | no |
 
 ## Example
 

sync/Cargo.toml

@@ -12,5 +12,9 @@ readme = "README.md"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
+[features]
+tracing = ["dep:tracing"]
+
 [dependencies]
 deadpool-runtime = { version = "0.1.2", path = "../runtime" }
+tracing = { version = "0.1", optional = true }

sync/src/lib.rs

@@ -114,10 +114,14 @@ where
         R: Send + 'static,
     {
         let arc = self.obj.clone();
+        #[cfg(feature = "tracing")]
+        let span = tracing::Span::current();
         self.runtime
             .spawn_blocking(move || {
                 let mut guard = arc.lock().unwrap();
                 let conn = guard.as_mut().unwrap();
+                #[cfg(feature = "tracing")]
+                let _span = span.enter();
                 f(conn)
             })
             .await