Add POSIX shared memory module for multiprocessing on Unix (#6498)

Copilot · youknowone · github-actions[bot] · web-flow · commit 8443b2c97e75 · 2025-12-25T14:54:44.000+09:00
---------

Co-authored-by: copilot-swe-agent[bot] &lt;198982749+Copilot@users.noreply.github.com&gt;
Co-authored-by: youknowone &lt;69878+youknowone@users.noreply.github.com&gt;
Co-authored-by: github-actions[bot] &lt;github-actions[bot]@users.noreply.github.com&gt;
diff --git a/.cspell.json b/.cspell.json
@@ -124,6 +124,8 @@
     "wasi",
     "zelf",
     // unix
+    "posixshmem",
+    "shm",
     "CLOEXEC",
     "codeset",
     "endgrent",
diff --git a/crates/stdlib/src/lib.rs b/crates/stdlib/src/lib.rs
@@ -57,6 +57,8 @@ mod faulthandler;
 mod fcntl;
 #[cfg(not(target_arch = "wasm32"))]
 mod multiprocessing;
+#[cfg(all(unix, not(target_os = "redox"), not(target_os = "android")))]
+mod posixshmem;
 #[cfg(unix)]
 mod posixsubprocess;
 // libc is missing constants on redox
@@ -190,6 +192,10 @@ pub fn get_module_inits() -> impl Iterator<Item = (Cow<'static, str>, StdlibInit
         {
             "_posixsubprocess" => posixsubprocess::make_module,
         }
+        #[cfg(all(unix, not(target_os = "redox"), not(target_os = "android")))]
+        {
+            "_posixshmem" => posixshmem::make_module,
+        }
         #[cfg(any(unix, windows))]
         {
             "mmap" => mmap::make_module,
diff --git a/crates/stdlib/src/posixshmem.rs b/crates/stdlib/src/posixshmem.rs
@@ -0,0 +1,48 @@
+#[cfg(all(unix, not(target_os = "redox"), not(target_os = "android")))]
+pub(crate) use _posixshmem::make_module;
+
+#[cfg(all(unix, not(target_os = "redox"), not(target_os = "android")))]
+#[pymodule]
+mod _posixshmem {
+    use std::ffi::CString;
+
+    use crate::{
+        common::os::errno_io_error,
+        vm::{
+            PyResult, VirtualMachine, builtins::PyStrRef, convert::IntoPyException,
+            function::OptionalArg,
+        },
+    };
+
+    #[pyfunction]
+    fn shm_open(
+        name: PyStrRef,
+        flags: libc::c_int,
+        mode: OptionalArg<libc::mode_t>,
+        vm: &VirtualMachine,
+    ) -> PyResult<libc::c_int> {
+        let name = CString::new(name.as_str()).map_err(|e| e.into_pyexception(vm))?;
+        let mode: libc::c_uint = mode.unwrap_or(0o600) as _;
+        #[cfg(target_os = "freebsd")]
+        let mode = mode.try_into().unwrap();
+        // SAFETY: `name` is a NUL-terminated string and `shm_open` does not write through it.
+        let fd = unsafe { libc::shm_open(name.as_ptr(), flags, mode) };
+        if fd == -1 {
+            Err(errno_io_error().into_pyexception(vm))
+        } else {
+            Ok(fd)
+        }
+    }
+
+    #[pyfunction]
+    fn shm_unlink(name: PyStrRef, vm: &VirtualMachine) -> PyResult<()> {
+        let name = CString::new(name.as_str()).map_err(|e| e.into_pyexception(vm))?;
+        // SAFETY: `name` is a valid NUL-terminated string and `shm_unlink` only reads it.
+        let ret = unsafe { libc::shm_unlink(name.as_ptr()) };
+        if ret == -1 {
+            Err(errno_io_error().into_pyexception(vm))
+        } else {
+            Ok(())
+        }
+    }
+}
diff --git a/extra_tests/snippets/builtin_posixshmem.py b/extra_tests/snippets/builtin_posixshmem.py
@@ -0,0 +1,12 @@
+import os
+import sys
+
+if os.name != "posix":
+    sys.exit(0)
+
+import _posixshmem
+
+name = f"/rp_posixshmem_{os.getpid()}"
+fd = _posixshmem.shm_open(name, os.O_CREAT | os.O_EXCL | os.O_RDWR, 0o600)
+os.close(fd)
+_posixshmem.shm_unlink(name)

Original file line number	Diff line number	Diff line change
`@@ -57,6 +57,8 @@ mod faulthandler;`
`57`	`57`	`mod fcntl;`
`58`	`58`	`#[cfg(not(target_arch = "wasm32"))]`
`59`	`59`	`mod multiprocessing;`
	`60`	`+#[cfg(all(unix, not(target_os = "redox"), not(target_os = "android")))]`
	`61`	`+mod posixshmem;`
`60`	`62`	`#[cfg(unix)]`
`61`	`63`	`mod posixsubprocess;`
`62`	`64`	`// libc is missing constants on redox`
`@@ -190,6 +192,10 @@ pub fn get_module_inits() -> impl Iterator<Item = (Cow<'static, str>, StdlibInit`
`190`	`192`	`{`
`191`	`193`	`"_posixsubprocess" => posixsubprocess::make_module,`
`192`	`194`	`}`
	`195`	`+ #[cfg(all(unix, not(target_os = "redox"), not(target_os = "android")))]`
	`196`	`+ {`
	`197`	`+ "_posixshmem" => posixshmem::make_module,`
	`198`	`+ }`
`193`	`199`	`#[cfg(any(unix, windows))]`
`194`	`200`	`{`
`195`	`201`	`"mmap" => mmap::make_module,`