fork safety

youknowone · youknowone · commit d95e4ab7698e · 2026-02-02T16:03:01.000+09:00
diff --git a/Cargo.lock b/Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
@@ -91,6 +91,8 @@ lto = "thin"
 [patch.crates-io]
 # REDOX START, Uncomment when you want to compile/check with redoxer
 # REDOX END
+# Fork-safety: expose reinit_after_fork() to reset global hash table after fork
+parking_lot_core = { git = "https://github.com/youknowone/parking_lot", rev = "e7c6c4e53a65d0143ffe417e2cc55c9467c3f3e1" }
 
 [package.metadata.packager]
 product-name = "RustPython"
@@ -184,6 +186,7 @@ num_enum = { version = "0.7", default-features = false }
 optional = "0.5"
 once_cell = "1.20.3"
 parking_lot = "0.12.3"
+parking_lot_core = { version = "0.9.12", features = ["fork"] }
 paste = "1.0.15"
 proc-macro2 = "1.0.105"
 pymath = { version = "0.1.5", features = ["mul_add", "malachite-bigint", "complex"] }
diff --git a/crates/vm/Cargo.toml b/crates/vm/Cargo.toml
@@ -64,6 +64,7 @@ num-traits = { workspace = true }
 num_enum = { workspace = true }
 once_cell = { workspace = true }
 parking_lot = { workspace = true }
+parking_lot_core = { workspace = true }
 paste = { workspace = true }
 scoped-tls = { workspace = true }
 scopeguard = { workspace = true }
diff --git a/crates/vm/src/stdlib/thread.rs b/crates/vm/src/stdlib/thread.rs
@@ -147,15 +147,9 @@ pub(crate) mod _thread {
 
         #[pymethod]
         fn _at_fork_reinit(&self, _vm: &VirtualMachine) -> PyResult<()> {
-            if self.mu.is_locked() {
-                unsafe {
-                    self.mu.unlock();
-                };
-            }
-            // Casting to AtomicCell is as unsafe as CPython code.
-            // Using AtomicCell will prevent compiler optimizer move it to somewhere later unsafe place.
-            // It will be not under the cell anymore after init call.
-
+            // Don't call unlock() &mdash; it may invoke unlock_slow() which accesses
+            // parking_lot_core's global hash table that is stale after fork().
+            // Just overwrite the mutex with a fresh INIT value.
             let new_mut = RawMutex::INIT;
             unsafe {
                 let old_mutex: &AtomicCell<RawMutex> = core::mem::transmute(&self.mu);
@@ -247,11 +241,9 @@ pub(crate) mod _thread {
 
         #[pymethod]
         fn _at_fork_reinit(&self, _vm: &VirtualMachine) -> PyResult<()> {
-            if self.mu.is_locked() {
-                unsafe {
-                    self.mu.unlock();
-                };
-            }
+            // Don't call unlock() &mdash; it may invoke unlock_slow() which accesses
+            // parking_lot_core's global hash table that is stale after fork().
+            // Just overwrite the mutex with a fresh INIT value.
             self.count.store(0, core::sync::atomic::Ordering::Relaxed);
             let new_mut = RawRMutex::INIT;
             unsafe {
