refactor(torture): probabilities handling

Effectively make the options 'commit-crash,' 'rollback,' and
'rollback-crash' reflect the actual probability of those actions
occurring at each iteration.

Author: gabriele-0201

torture/src/supervisor/cli.rs

@@ -63,25 +63,32 @@ pub struct WorkloadParams {
     #[arg(long = "random-size")]
     pub random_size: bool,
 
-    /// When exercising a new commit, the probability of causing it to crash.
+    /// When executing a workload iteration, this is the probability of executing a commit
+    /// and causing it to crash.
+    ///
+    /// The sum of `commit-crash`, `rollback` and `rollback-crash` must be lower than 100.
     ///
     /// Accepted values are in the range of 0 to 100
     #[clap(default_value = "20")]
     #[clap(value_parser=clap::value_parser!(u8).range(0..=100))]
     #[arg(long = "commit-crash")]
     pub crash: u8,
 
-    /// Instead of exercising a new commit, this is the probability of executing a rollback.
+    /// When executing a workload iteration ,this is the probability of executing a rollback.
+    ///
+    /// The sum of `commit-crash`, `rollback` and `rollback-crash` must be lower than 100.
     ///
     /// Accepted values are in the range of 0 to 100
     #[clap(default_value = "5")]
     #[clap(value_parser=clap::value_parser!(u8).range(0..=100))]
     #[arg(long = "rollback")]
     pub rollback: u8,
 
-    /// Instead of exercising a new commit, this is the probability of executing a rollback
+    /// When executing a workload iteration, this is the probability of executing a rollback
     /// and causing it to crash.
     ///
+    /// The sum of `commit-crash`, `rollback` and `rollback-crash` must be lower than 100.
+    ///
     /// Accepted values are in the range of 0 to 100
     #[clap(default_value = "5")]
     #[clap(value_parser=clap::value_parser!(u8).range(0..=100))]

torture/src/supervisor/workload.rs

@@ -1,6 +1,6 @@
 use anyhow::Result;
 use imbl::OrdMap;
-use rand::prelude::*;
+use rand::{distributions::WeightedIndex, prelude::*};
 use std::time::Duration;
 use tempfile::TempDir;
 use tokio::time::{error::Elapsed, timeout};
@@ -28,31 +28,39 @@ struct Biases {
     /// When generating a key, whether it should be one that was appeared somewhere or a brand new
     /// key.
     new_key: f64,
-    /// When exercising a new commit, the probability of causing it to crash.
-    crash: f64,
-    /// Instead of exercising a new commit, this is the probability of executing a rollback.
-    rollback: f64,
-    /// Instead of exercising a new commit, this is the probability of executing a rollback
+    /// When executing a workload iteration, this is the probability of executing a commit.
+    commit: u8,
+    /// When executing a workload iteration, this is the probability of executing a commit
     /// and causing it to crash.
-    rollback_crash: f64,
+    commit_crash: u8,
+    /// When executing a workload iteration ,this is the probability of executing a rollback.
+    rollback: u8,
+    /// When executing a workload iteration, this is the probability of executing a rollback
+    /// and causing it to crash.
+    rollback_crash: u8,
 }
 
 impl Biases {
     fn new(
         delete: u8,
         overflow: u8,
         new_key: u8,
-        crash: u8,
+        commit_crash: u8,
         rollback: u8,
         rollback_crash: u8,
     ) -> Self {
+        let Some(commit) = 100u8.checked_sub(commit_crash + rollback + rollback_crash) else {
+            panic!("Sum of `commit-crash`, `rollback` and `rollback-crash` must be lower than 100");
+        };
+
         Self {
             delete: (delete as f64) / 100.0,
             overflow: (overflow as f64) / 100.0,
             new_key: (new_key as f64) / 100.0,
-            crash: (crash as f64) / 100.0,
-            rollback: (rollback as f64) / 100.0,
-            rollback_crash: (rollback_crash as f64) / 100.0,
+            commit,
+            commit_crash,
+            rollback,
+            rollback_crash,
         }
     }
 }
@@ -310,22 +318,22 @@ impl Workload {
         let rr = agent.rr().clone();
         trace!("run_iteration");
 
-        if self.state.rng.gen_bool(self.state.biases.rollback_crash) {
-            self.exercise_rollback_crashing(&rr).await?;
-            return Ok(());
-        }
-
-        if self.state.rng.gen_bool(self.state.biases.rollback) {
-            self.exercise_rollback(&rr).await?;
-            return Ok(());
-        }
-
-        if self.state.rng.gen_bool(self.state.biases.crash) {
-            self.exercise_commit_crashing(&rr).await?;
-            return Ok(());
+        let dist = WeightedIndex::new([
+            self.state.biases.commit,
+            self.state.biases.commit_crash,
+            self.state.biases.rollback,
+            self.state.biases.rollback_crash,
+        ])
+        .unwrap();
+
+        match self.state.rng.sample(dist) {
+            0 => self.exercise_commit(&rr).await?,
+            1 => self.exercise_commit_crashing(&rr).await?,
+            2 => self.exercise_rollback(&rr).await?,
+            3 => self.exercise_rollback_crashing(&rr).await?,
+            _ => unreachable!(),
         }
 
-        self.exercise_commit(&rr).await?;
         Ok(())
     }
 
@@ -646,7 +654,7 @@ impl Workload {
         assert!(self.agent.is_none());
         controller::spawn_agent_into(&mut self.agent).await?;
         let workdir = self.workdir.path().display().to_string();
-        let rollback = self.state.biases.rollback > 0.0;
+        let rollback = self.state.biases.rollback > 0;
         self.agent
             .as_mut()
             .unwrap()