2 files changed, 44 insertions, 12 deletions

diff --git a/crates/profile/src/google_cpu_profiler.rs b/crates/profile/src/google_cpu_profiler.rs
index db865c65b..cae6caeaa 100644
--- a/crates/profile/src/google_cpu_profiler.rs
+++ b/crates/profile/src/google_cpu_profiler.rs
@@ -14,26 +14,31 @@ extern "C" {
     fn ProfilerStop();
 }
 
-static PROFILER_STATE: AtomicUsize = AtomicUsize::new(OFF);
 const OFF: usize = 0;
 const ON: usize = 1;
 const PENDING: usize = 2;
 
-pub fn start(path: &Path) {
-    if PROFILER_STATE.compare_and_swap(OFF, PENDING, Ordering::SeqCst) != OFF {
+fn transition(current: usize, new: usize) -> bool {
+    static STATE: AtomicUsize = AtomicUsize::new(OFF);
+
+    STATE.compare_exchange(current, new, Ordering::SeqCst, Ordering::SeqCst).is_ok()
+}
+
+pub(crate) fn start(path: &Path) {
+    if !transition(OFF, PENDING) {
         panic!("profiler already started");
     }
     let path = CString::new(path.display().to_string()).unwrap();
     if unsafe { ProfilerStart(path.as_ptr()) } == 0 {
         panic!("profiler failed to start")
     }
-    assert!(PROFILER_STATE.compare_and_swap(PENDING, ON, Ordering::SeqCst) == PENDING);
+    assert!(transition(PENDING, ON));
 }
 
-pub fn stop() {
-    if PROFILER_STATE.compare_and_swap(ON, PENDING, Ordering::SeqCst) != ON {
+pub(crate) fn stop() {
+    if !transition(ON, PENDING) {
         panic!("profiler is not started")
     }
     unsafe { ProfilerStop() };
-    assert!(PROFILER_STATE.compare_and_swap(PENDING, OFF, Ordering::SeqCst) == PENDING);
+    assert!(transition(PENDING, OFF));
 }
diff --git a/crates/profile/src/lib.rs b/crates/profile/src/lib.rs
index 9ca6341db..a31fb8f43 100644
--- a/crates/profile/src/lib.rs
+++ b/crates/profile/src/lib.rs
@@ -52,7 +52,7 @@ impl Drop for Scope {
 /// Usage:
 /// 1. Install gpref_tools (https://github.com/gperftools/gperftools), probably packaged with your Linux distro.
 /// 2. Build with `cpu_profiler` feature.
-/// 3. Tun the code, the *raw* output would be in the `./out.profile` file.
+/// 3. Run the code, the *raw* output would be in the `./out.profile` file.
 /// 4. Install pprof for visualization (https://github.com/google/pprof).
 /// 5. Bump sampling frequency to once per ms: `export CPUPROFILE_FREQUENCY=1000`
 /// 6. Use something like `pprof -svg target/release/rust-analyzer ./out.profile` to see the results.
@@ -60,8 +60,17 @@ impl Drop for Scope {
 /// For example, here's how I run profiling on NixOS:
 ///
 /// ```bash
-/// $ nix-shell -p gperftools --run \
-///     'cargo run --release -p rust-analyzer -- parse < ~/projects/rustbench/parser.rs > /dev/null'
+/// $ bat -p shell.nix
+/// with import <nixpkgs> {};
+/// mkShell {
+///   buildInputs = [ gperftools ];
+///   shellHook = ''
+///     export LD_LIBRARY_PATH="${gperftools}/lib:"
+///   '';
+/// }
+/// $ set -x CPUPROFILE_FREQUENCY 1000
+/// $ nix-shell --run 'cargo test --release --package rust-analyzer --lib -- benchmarks::benchmark_integrated_highlighting --exact --nocapture'
+/// $ pprof -svg target/release/deps/rust_analyzer-8739592dc93d63cb crates/rust-analyzer/out.profile > profile.svg
 /// ```
 ///
 /// See this diff for how to profile completions:
@@ -81,7 +90,9 @@ pub fn cpu_span() -> CpuSpan {
 
     #[cfg(not(feature = "cpu_profiler"))]
     {
-        eprintln!("cpu_profiler feature is disabled")
+        eprintln!(
+            r#"cpu profiling is disabled, uncomment `default = [ "cpu_profiler" ]` in Cargo.toml to enable."#
+        )
     }
 
     CpuSpan { _private: () }
@@ -91,7 +102,23 @@ impl Drop for CpuSpan {
     fn drop(&mut self) {
         #[cfg(feature = "cpu_profiler")]
         {
-            google_cpu_profiler::stop()
+            google_cpu_profiler::stop();
+            let profile_data = std::env::current_dir().unwrap().join("out.profile");
+            eprintln!("Profile data saved to:\n\n    {}\n", profile_data.display());
+            let mut cmd = std::process::Command::new("pprof");
+            cmd.arg("-svg").arg(std::env::current_exe().unwrap()).arg(&profile_data);
+            let out = cmd.output();
+
+            match out {
+                Ok(out) if out.status.success() => {
+                    let svg = profile_data.with_extension("svg");
+                    std::fs::write(&svg, &out.stdout).unwrap();
+                    eprintln!("Profile rendered to:\n\n    {}\n", svg.display());
+                }
+                _ => {
+                    eprintln!("Failed to run:\n\n   {:?}\n", cmd);
+                }
+            }
         }
     }
 }