fix(exec-harness): improve simulation script support and detect subprocesses

Author: GuillaumeLagrange

crates/exec-harness/preload/codspeed_preload.c

@@ -7,8 +7,6 @@
 //
 // Environment variables:
 //   CODSPEED_BENCH_URI - The benchmark URI to report (required)
-//   CODSPEED_PRELOAD_LOCK - Set by the first process to prevent child processes
-//                          from re-initializing instrumentation
 
 #include <stdlib.h>
 #include <unistd.h>
@@ -22,8 +20,6 @@
 #define RUNNING_ON_VALGRIND 0
 #endif
 
-static const char *LOCK_ENV = "CODSPEED_PRELOAD_LOCK";
-
 // These constants are defined by the build script (build.rs) via -D flags
 #ifndef CODSPEED_URI_ENV
 #error "CODSPEED_URI_ENV must be defined by the build system"
@@ -54,14 +50,6 @@ __attribute__((constructor)) static void codspeed_preload_init(void) {
     return;
   }
 
-  // Check if another process already owns the instrumentation
-  if (getenv(LOCK_ENV)) {
-    return;
-  }
-
-  // Set the lock to prevent child processes from initializing
-  setenv(LOCK_ENV, "1", 1);
-
   g_bench_uri = getenv(URI_ENV);
   if (!g_bench_uri) {
     return;

crates/exec-harness/src/analysis/mod.rs

@@ -6,6 +6,7 @@ use crate::BenchmarkCommand;
 use crate::constants;
 use crate::uri;
 use instrument_hooks_bindings::InstrumentHooks;
+use std::path::PathBuf;
 use std::process::Command;
 
 mod ld_preload_check;
@@ -57,7 +58,11 @@ pub fn perform_with_valgrind(commands: Vec<BenchmarkCommand>) -> Result<()> {
         cmd.env("PYTHONPERFSUPPORT", "1");
         cmd.env(constants::URI_ENV, &name_and_uri.uri);
 
-        let status = cmd.status().context("Failed to execute command")?;
+        let mut child = cmd.spawn().context("Failed to spawn command")?;
+
+        let status = child.wait().context("Failed to execute command")?;
+
+        bail_if_command_spawned_subprocesses_under_valgrind(child.id())?;
 
         if !status.success() {
             bail!("Command exited with non-zero status: {status}");
@@ -66,3 +71,35 @@ pub fn perform_with_valgrind(commands: Vec<BenchmarkCommand>) -> Result<()> {
 
     Ok(())
 }
+
+fn bail_if_command_spawned_subprocesses_under_valgrind(pid: u32) -> Result<()> {
+    let Some(profile_folder) = std::env::var_os("CODSPEED_PROFILE_FOLDER") else {
+        debug!("CODSPEED_PROFILE_FOLDER is not set, skipping subprocess detection");
+        return Ok(());
+    };
+
+    let profile_folder = PathBuf::from(profile_folder);
+
+    // Bail if any <pid>.out where <pid> > pid of the benchmark process exists in the profile
+    // folder, which indicates that the benchmark process spawned subprocesses.
+    for entry in std::fs::read_dir(profile_folder)? {
+        let entry = entry?;
+        let file_name = entry.file_name();
+        let file_name = file_name.to_string_lossy();
+
+        if let Some(stripped) = file_name.strip_suffix(".out") {
+            if let Ok(subprocess_pid) = stripped.parse::<u32>() {
+                if subprocess_pid > pid {
+                    bail!(
+                        "The codspeed CLI in CPU Simulation mode does not support measuring processes that spawn other processes yet.\n\n\
+                         Please either:\n\
+                         - Use the walltime measurement mode, or\n\
+                         - Benchmark a process that does not create subprocesses"
+                    )
+                }
+            }
+        }
+    }
+
+    Ok(())
+}