Fix #100 - obtain timestamp early

src/main.rs

@@ -67,6 +67,12 @@ enum Commands {
 }
 
 fn main() {
+    // Obtain the time stamp early so that it more properly reflects the time the sample was
+    // obtained, not the time when reporting was allowed to run.  The latter is subject to greater
+    // system effects, and using that timestamp increases the risk that the samples' timestamp order
+    // improperly reflects the true order in which they were obtained.  See #100.
+    let timestamp = util::time_iso8601();
+
     env_logger::init();
 
     let cli = Cli::parse();
@@ -102,10 +108,10 @@ fn main() {
             };
             if *batchless {
                 let mut jm = batchless::BatchlessJobManager::new();
-                ps::create_snapshot(&mut jm, &opts);
+                ps::create_snapshot(&mut jm, &opts, &timestamp);
             } else {
                 let mut jm = slurm::SlurmJobManager {};
-                ps::create_snapshot(&mut jm, &opts);
+                ps::create_snapshot(&mut jm, &opts, &timestamp);
             }
         }
         Commands::Analyze {} => {

src/ps.rs

@@ -9,8 +9,8 @@ use crate::jobs;
 use crate::nvidia;
 use crate::process;
 use crate::procfs;
+use crate::util::three_places;
 use crate::procfsapi;
-use crate::util::{three_places, time_iso8601};
 
 use csv::{Writer, WriterBuilder};
 use std::collections::{HashMap, HashSet};
@@ -163,7 +163,7 @@ pub struct PsOptions<'a> {
     pub exclude_commands: Vec<&'a str>,
 }
 
-pub fn create_snapshot(jobs: &mut dyn jobs::JobManager, opts: &PsOptions) {
+pub fn create_snapshot(jobs: &mut dyn jobs::JobManager, opts: &PsOptions, timestamp: &str) {
     let no_gpus = empty_gpuset();
     let mut proc_by_pid = ProcTable::new();
 
@@ -313,13 +313,12 @@ pub fn create_snapshot(jobs: &mut dyn jobs::JobManager, opts: &PsOptions) {
         .flexible(true)
         .from_writer(io::stdout());
 
-    let timestamp = time_iso8601();
     let hostname = hostname::get().unwrap().into_string().unwrap();
     let num_cores = num_cpus::get();
     const VERSION: &str = env!("CARGO_PKG_VERSION");
     let print_params = PrintParameters {
         hostname: &hostname,
-        timestamp: &timestamp,
+        timestamp: timestamp,
         num_cores,
         version: VERSION,
         opts,