fix(madsim): fix determinism for getrandom (#202)

* fix determinism for getrandom Signed-off-by: Runji Wang <[email protected]> * bump version Signed-off-by: Runji Wang <[email protected]> * fix in another way Signed-off-by: Runji Wang <[email protected]> --------- Signed-off-by: Runji Wang <[email protected]>
madsim-rs · Apr 7, 2024 · e9aa251 · e9aa251
1 parent 4ebdbcd
commit e9aa251
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -6,6 +6,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## madsim [0.2.27] - 2024-04-07
+
+### Fixed
+
+- Fix the problem that `getrandom` returns different values in multiple runs with the same seed.
+
 ## rdkafka [0.3.4] - 2024-03-22
 
 ### Fixed

diff --git a/Cargo.toml b/Cargo.toml
@@ -11,3 +11,6 @@ members = [
     "tonic-example",
 ]
 resolver = "2"
+
+[patch.crates-io]
+getrandom = { git = "https://github.com/madsim-rs/getrandom.git", rev = "6c9d9e9" }
diff --git a/madsim/Cargo.toml b/madsim/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "madsim"
-version = "0.2.26"
+version = "0.2.27"
 edition = "2021"
 authors = ["Runji Wang <[email protected]>"]
 description = "Deterministic Simulator for distributed systems."
@@ -63,6 +63,7 @@ tokio-util = { version = "0.7", features = ["codec"] }
 criterion = "0.5"
 structopt = "0.3"
 tokio = { version = "1", features = ["rt-multi-thread", "macros", "io-util"] }
+getrandom = "=0.2.13"
 
 [[bench]]
 name = "rpc"

diff --git a/madsim/src/sim/rand.rs b/madsim/src/sim/rand.rs
@@ -208,8 +208,11 @@ unsafe extern "C" fn getrandom(mut buf: *mut u8, mut buflen: usize, _flags: u32)
             buf = buf.add(std::mem::size_of::<u64>());
             buflen -= std::mem::size_of::<u64>();
         }
-        let val = rand.with(|rng| rng.gen::<u64>().to_ne_bytes());
-        core::ptr::copy(val.as_ptr(), buf, buflen);
+        // note: do not modify state if buflen == 0
+        if buflen != 0 {
+            let val = rand.with(|rng| rng.gen::<u64>().to_ne_bytes());
+            core::ptr::copy(val.as_ptr(), buf, buflen);
+        }
         return len as _;
     }
     #[cfg(target_os = "linux")]
@@ -265,7 +268,7 @@ unsafe extern "C" fn getentropy(buf: *mut u8, buflen: usize) -> i32 {
 #[cfg(test)]
 mod tests {
     use crate::runtime::Runtime;
-    use std::collections::{BTreeSet, HashMap};
+    use std::collections::{BTreeSet, HashMap, HashSet};
 
     #[test]
     #[cfg_attr(target_os = "linux", ignore)]
@@ -305,4 +308,30 @@ mod tests {
         }
         assert_eq!(seqs.len(), 3, "hashmap is not deterministic");
     }
+
+    // https://github.com/madsim-rs/madsim/issues/201
+    #[test]
+    fn getrandom_should_be_deterministic() {
+        let rnd_fn = || async {
+            let mut dst = [0];
+            getrandom::getrandom(&mut dst).unwrap();
+            dst
+        };
+        let builder = crate::runtime::Builder::from_env();
+        let seed = builder.seed;
+        let set = (0..10)
+            .map(|_| {
+                crate::runtime::Builder {
+                    seed,
+                    count: 1,
+                    jobs: 1,
+                    config: crate::Config::default(),
+                    time_limit: None,
+                    check: false,
+                }
+                .run(rnd_fn)
+            })
+            .collect::<HashSet<_>>();
+        assert_eq!(set.len(), 1);
+    }
 }