don't refresh system stats when only reporting process stats (#784)

src/agent/onefuzz-agent/src/tasks/fuzz/libfuzzer_fuzz.rs

@@ -301,12 +301,15 @@ fn try_report_iter_update(
 }
 
 async fn report_fuzzer_sys_info(worker_id: usize, run_id: Uuid, fuzzer_pid: u32) -> Result<()> {
-    loop {
-        system::refresh()?;
-
     // Allow for sampling CPU usage.
     time::delay_for(PROC_INFO_COLLECTION_DELAY).await;
 
+    loop {
+        // process doesn't exist
+        if !system::refresh_process(fuzzer_pid)? {
+            break;
+        }
+
         if let Some(proc_info) = system::proc_info(fuzzer_pid)? {
             event!(process_stats;
                EventData::WorkerId = worker_id,

src/agent/onefuzz/src/system.rs

@@ -22,6 +22,11 @@ pub fn proc_info(pid: u32) -> Result<Option<ProcInfo>> {
     Ok(s.proc_info(pid))
 }
 
+pub fn refresh_process(pid: u32) -> Result<bool> {
+    let mut s = SYSTEM.write().map_err(|e| format_err!("{}", e))?;
+    Ok(s.refresh_process(pid))
+}
+
 lazy_static! {
     static ref SYSTEM: RwLock<System> = {
         let mut s = System::new();
@@ -56,6 +61,10 @@ impl System {
         self.system.refresh_all();
     }
 
+    pub fn refresh_process(&mut self, pid: u32) -> bool {
+        self.system.refresh_process(pid as Pid)
+    }
+
     pub fn system_info(&self) -> SystemInfo {
         let system = &self.system;