sampling: move serialization into "sampling" crate

Summary: This way any code can skip tracing and directly output a "sampled" value. I want to log a list of values, which isn't convenient using tracing.

Reviewed By: quark-zju

Differential Revision: D49509125

fbshipit-source-id: c6a684dcb7a13572460ddb9a7678ffebee80f9ce

eden/scm/lib/sampling/Cargo.toml

@@ -9,4 +9,6 @@ edition = "2021"
 configmodel = { version = "0.1.0", path = "../config/model" }
 once_cell = "1.12"
 parking_lot = { version = "0.12.1", features = ["send_guard"] }
+serde = { version = "1.0.185", features = ["derive", "rc"] }
+serde_json = { version = "1.0.100", features = ["float_roundtrip", "unbounded_depth"] }
 tracing = "0.1.35"

eden/scm/lib/sampling/src/lib.rs

@@ -15,6 +15,10 @@ use std::sync::Arc;
 use once_cell::sync::OnceCell;
 use parking_lot::Mutex;
 use parking_lot::MutexGuard;
+use serde::ser::Serialize;
+use serde::ser::SerializeMap;
+use serde::Serializer;
+use serde_json::Serializer as JsonSerializer;
 
 pub static CONFIG: OnceCell<Option<Arc<SamplingConfig>>> = OnceCell::new();
 
@@ -86,6 +90,23 @@ impl SamplingConfig {
     pub fn file(&self) -> MutexGuard<File> {
         self.file.lock()
     }
+
+    pub fn append<V: ?Sized>(&self, category: &str, value: &V) -> std::io::Result<()>
+    where
+        V: Serialize,
+    {
+        let mut file = self.file();
+        let mut serializer = JsonSerializer::new(&*file);
+
+        let mut serializer = serializer.serialize_map(None)?;
+        serializer.serialize_entry("category", category)?;
+        serializer.serialize_entry("data", value)?;
+        serializer.end()?;
+
+        file.write_all(b"\0")?;
+
+        Ok(())
+    }
 }
 
 // Returns tuple of output path and whether it's okay if the path already exists.

eden/scm/lib/tracing-sampler/Cargo.toml

@@ -8,8 +8,6 @@ edition = "2021"
 [dependencies]
 once_cell = "1.12"
 sampling = { version = "0.1.0", path = "../sampling" }
-serde = { version = "1.0.185", features = ["derive", "rc"] }
-serde_json = { version = "1.0.100", features = ["float_roundtrip", "unbounded_depth"] }
 tracing = "0.1.35"
 tracing-serde = "0.1.3"
 tracing-subscriber = { version = "0.3.17", features = ["ansi", "env-filter", "fmt", "json", "local-time", "parking_lot", "registry"] }

eden/scm/lib/tracing-sampler/src/lib.rs

@@ -5,14 +5,10 @@
  * GNU General Public License version 2.
  */
 
-use std::io::Write;
 use std::sync::Arc;
 
 use once_cell::sync::OnceCell;
 use sampling::SamplingConfig;
-use serde::ser::SerializeMap;
-use serde::ser::Serializer;
-use serde_json::Serializer as JsonSerializer;
 use tracing::subscriber::Interest;
 use tracing::Event;
 use tracing::Metadata;
@@ -51,21 +47,7 @@ impl<S: Subscriber> Layer<S> for SamplingLayer {
             None => return,
         };
 
-        let serialize = || -> std::io::Result<()> {
-            let mut file = config.file();
-            let mut serializer = JsonSerializer::new(&*file);
-
-            let mut serializer = serializer.serialize_map(None)?;
-            serializer.serialize_entry("category", category)?;
-            serializer.serialize_entry("data", &event.field_map())?;
-            serializer.end()?;
-
-            file.write_all(b"\0")?;
-
-            Ok(())
-        };
-
-        let _ = serialize();
+        let _ = config.append(category, &event.field_map());
     }
 }