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Move ShmemHandle into separate module, tweak documentation (#12595)

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Initial PR for the hashmap behind the updated LFC implementation. This
refactors `neon-shmem` so that the actual shared memory utilities are in
a separate module within the crate. Beyond that, it slightly changes
some of the docstrings so that they play nicer with `cargo doc`.
This commit is contained in:
quantumish
2025-07-15 10:40:40 -07:00
committed by GitHub
parent 5c934efb29
commit 809633903d
2 changed files with 410 additions and 418 deletions
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419
libs/neon-shmem/src/lib.rs
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@@ -1,418 +1 @@
//! Shared memory utilities for neon communicator
use std::num::NonZeroUsize;
use std::os::fd::{AsFd, BorrowedFd, OwnedFd};
use std::ptr::NonNull;
use std::sync::atomic::{AtomicUsize, Ordering};
use nix::errno::Errno;
use nix::sys::mman::MapFlags;
use nix::sys::mman::ProtFlags;
use nix::sys::mman::mmap as nix_mmap;
use nix::sys::mman::munmap as nix_munmap;
use nix::unistd::ftruncate as nix_ftruncate;
/// ShmemHandle represents a shared memory area that can be shared by processes over fork().
/// Unlike shared memory allocated by Postgres, this area is resizable, up to 'max_size' that's
/// specified at creation.
///
/// The area is backed by an anonymous file created with memfd_create(). The full address space for
/// 'max_size' is reserved up-front with mmap(), but whenever you call [`ShmemHandle::set_size`],
/// the underlying file is resized. Do not access the area beyond the current size. Currently, that
/// will cause the file to be expanded, but we might use mprotect() etc. to enforce that in the
/// future.
pub struct ShmemHandle {
/// memfd file descriptor
fd: OwnedFd,
max_size: usize,
// Pointer to the beginning of the shared memory area. The header is stored there.
shared_ptr: NonNull<SharedStruct>,
// Pointer to the beginning of the user data
pub data_ptr: NonNull<u8>,
}
/// This is stored at the beginning in the shared memory area.
struct SharedStruct {
max_size: usize,
/// Current size of the backing file. The high-order bit is used for the RESIZE_IN_PROGRESS flag
current_size: AtomicUsize,
}
const RESIZE_IN_PROGRESS: usize = 1 << 63;
const HEADER_SIZE: usize = std::mem::size_of::<SharedStruct>();
/// Error type returned by the ShmemHandle functions.
#[derive(thiserror::Error, Debug)]
#[error("{msg}: {errno}")]
pub struct Error {
pub msg: String,
pub errno: Errno,
}
impl Error {
fn new(msg: &str, errno: Errno) -> Error {
Error {
msg: msg.to_string(),
errno,
}
}
}
impl ShmemHandle {
/// Create a new shared memory area. To communicate between processes, the processes need to be
/// fork()'d after calling this, so that the ShmemHandle is inherited by all processes.
///
/// If the ShmemHandle is dropped, the memory is unmapped from the current process. Other
/// processes can continue using it, however.
pub fn new(name: &str, initial_size: usize, max_size: usize) -> Result<ShmemHandle, Error> {
// create the backing anonymous file.
let fd = create_backing_file(name)?;
Self::new_with_fd(fd, initial_size, max_size)
}
fn new_with_fd(
fd: OwnedFd,
initial_size: usize,
max_size: usize,
) -> Result<ShmemHandle, Error> {
// We reserve the high-order bit for the RESIZE_IN_PROGRESS flag, and the actual size
// is a little larger than this because of the SharedStruct header. Make the upper limit
// somewhat smaller than that, because with anything close to that, you'll run out of
// memory anyway.
if max_size >= 1 << 48 {
panic!("max size {max_size} too large");
}
if initial_size > max_size {
panic!("initial size {initial_size} larger than max size {max_size}");
}
// The actual initial / max size is the one given by the caller, plus the size of
// 'SharedStruct'.
let initial_size = HEADER_SIZE + initial_size;
let max_size = NonZeroUsize::new(HEADER_SIZE + max_size).unwrap();
// Reserve address space for it with mmap
//
// TODO: Use MAP_HUGETLB if possible
let start_ptr = unsafe {
nix_mmap(
None,
max_size,
ProtFlags::PROT_READ | ProtFlags::PROT_WRITE,
MapFlags::MAP_SHARED,
&fd,
0,
)
}
.map_err(|e| Error::new("mmap failed: {e}", e))?;
// Reserve space for the initial size
enlarge_file(fd.as_fd(), initial_size as u64)?;
// Initialize the header
let shared: NonNull<SharedStruct> = start_ptr.cast();
unsafe {
shared.write(SharedStruct {
max_size: max_size.into(),
current_size: AtomicUsize::new(initial_size),
})
};
// The user data begins after the header
let data_ptr = unsafe { start_ptr.cast().add(HEADER_SIZE) };
Ok(ShmemHandle {
fd,
max_size: max_size.into(),
shared_ptr: shared,
data_ptr,
})
}
// return reference to the header
fn shared(&self) -> &SharedStruct {
unsafe { self.shared_ptr.as_ref() }
}
/// Resize the shared memory area. 'new_size' must not be larger than the 'max_size' specified
/// when creating the area.
///
/// This may only be called from one process/thread concurrently. We detect that case
/// and return an Error.
pub fn set_size(&self, new_size: usize) -> Result<(), Error> {
let new_size = new_size + HEADER_SIZE;
let shared = self.shared();
if new_size > self.max_size {
panic!(
"new size ({} is greater than max size ({})",
new_size, self.max_size
);
}
assert_eq!(self.max_size, shared.max_size);
// Lock the area by setting the bit in 'current_size'
//
// Ordering::Relaxed would probably be sufficient here, as we don't access any other memory
// and the posix_fallocate/ftruncate call is surely a synchronization point anyway. But
// since this is not performance-critical, better safe than sorry .
let mut old_size = shared.current_size.load(Ordering::Acquire);
loop {
if (old_size & RESIZE_IN_PROGRESS) != 0 {
return Err(Error::new(
"concurrent resize detected",
Errno::UnknownErrno,
));
}
match shared.current_size.compare_exchange(
old_size,
new_size,
Ordering::Acquire,
Ordering::Relaxed,
) {
Ok(_) => break,
Err(x) => old_size = x,
}
}
// Ok, we got the lock.
//
// NB: If anything goes wrong, we *must* clear the bit!
let result = {
use std::cmp::Ordering::{Equal, Greater, Less};
match new_size.cmp(&old_size) {
Less => nix_ftruncate(&self.fd, new_size as i64).map_err(|e| {
Error::new("could not shrink shmem segment, ftruncate failed: {e}", e)
}),
Equal => Ok(()),
Greater => enlarge_file(self.fd.as_fd(), new_size as u64),
}
};
// Unlock
shared.current_size.store(
if result.is_ok() { new_size } else { old_size },
Ordering::Release,
);
result
}
/// Returns the current user-visible size of the shared memory segment.
///
/// NOTE: a concurrent set_size() call can change the size at any time. It is the caller's
/// responsibility not to access the area beyond the current size.
pub fn current_size(&self) -> usize {
let total_current_size =
self.shared().current_size.load(Ordering::Relaxed) & !RESIZE_IN_PROGRESS;
total_current_size - HEADER_SIZE
}
}
impl Drop for ShmemHandle {
fn drop(&mut self) {
// SAFETY: The pointer was obtained from mmap() with the given size.
// We unmap the entire region.
let _ = unsafe { nix_munmap(self.shared_ptr.cast(), self.max_size) };
// The fd is dropped automatically by OwnedFd.
}
}
/// Create a "backing file" for the shared memory area. On Linux, use memfd_create(), to create an
/// anonymous in-memory file. One macos, fall back to a regular file. That's good enough for
/// development and testing, but in production we want the file to stay in memory.
///
/// disable 'unused_variables' warnings, because in the macos path, 'name' is unused.
#[allow(unused_variables)]
fn create_backing_file(name: &str) -> Result<OwnedFd, Error> {
#[cfg(not(target_os = "macos"))]
{
nix::sys::memfd::memfd_create(name, nix::sys::memfd::MFdFlags::empty())
.map_err(|e| Error::new("memfd_create failed: {e}", e))
}
#[cfg(target_os = "macos")]
{
let file = tempfile::tempfile().map_err(|e| {
Error::new(
"could not create temporary file to back shmem area: {e}",
nix::errno::Errno::from_raw(e.raw_os_error().unwrap_or(0)),
)
})?;
Ok(OwnedFd::from(file))
}
}
fn enlarge_file(fd: BorrowedFd, size: u64) -> Result<(), Error> {
// Use posix_fallocate() to enlarge the file. It reserves the space correctly, so that
// we don't get a segfault later when trying to actually use it.
#[cfg(not(target_os = "macos"))]
{
nix::fcntl::posix_fallocate(fd, 0, size as i64).map_err(|e| {
Error::new(
"could not grow shmem segment, posix_fallocate failed: {e}",
e,
)
})
}
// As a fallback on macos, which doesn't have posix_fallocate, use plain 'fallocate'
#[cfg(target_os = "macos")]
{
nix::unistd::ftruncate(fd, size as i64)
.map_err(|e| Error::new("could not grow shmem segment, ftruncate failed: {e}", e))
}
}
#[cfg(test)]
mod tests {
use super::*;
use nix::unistd::ForkResult;
use std::ops::Range;
/// check that all bytes in given range have the expected value.
fn assert_range(ptr: *const u8, expected: u8, range: Range<usize>) {
for i in range {
let b = unsafe { *(ptr.add(i)) };
assert_eq!(expected, b, "unexpected byte at offset {i}");
}
}
/// Write 'b' to all bytes in the given range
fn write_range(ptr: *mut u8, b: u8, range: Range<usize>) {
unsafe { std::ptr::write_bytes(ptr.add(range.start), b, range.end - range.start) };
}
// simple single-process test of growing and shrinking
#[test]
fn test_shmem_resize() -> Result<(), Error> {
let max_size = 1024 * 1024;
let init_struct = ShmemHandle::new("test_shmem_resize", 0, max_size)?;
assert_eq!(init_struct.current_size(), 0);
// Initial grow
let size1 = 10000;
init_struct.set_size(size1).unwrap();
assert_eq!(init_struct.current_size(), size1);
// Write some data
let data_ptr = init_struct.data_ptr.as_ptr();
write_range(data_ptr, 0xAA, 0..size1);
assert_range(data_ptr, 0xAA, 0..size1);
// Shrink
let size2 = 5000;
init_struct.set_size(size2).unwrap();
assert_eq!(init_struct.current_size(), size2);
// Grow again
let size3 = 20000;
init_struct.set_size(size3).unwrap();
assert_eq!(init_struct.current_size(), size3);
// Try to read it. The area that was shrunk and grown again should read as all zeros now
assert_range(data_ptr, 0xAA, 0..5000);
assert_range(data_ptr, 0, 5000..size1);
// Try to grow beyond max_size
//let size4 = max_size + 1;
//assert!(init_struct.set_size(size4).is_err());
// Dropping init_struct should unmap the memory
drop(init_struct);
Ok(())
}
/// This is used in tests to coordinate between test processes. It's like std::sync::Barrier,
/// but is stored in the shared memory area and works across processes. It's implemented by
/// polling, because e.g. standard rust mutexes are not guaranteed to work across processes.
struct SimpleBarrier {
num_procs: usize,
count: AtomicUsize,
}
impl SimpleBarrier {
unsafe fn init(ptr: *mut SimpleBarrier, num_procs: usize) {
unsafe {
*ptr = SimpleBarrier {
num_procs,
count: AtomicUsize::new(0),
}
}
}
pub fn wait(&self) {
let old = self.count.fetch_add(1, Ordering::Relaxed);
let generation = old / self.num_procs;
let mut current = old + 1;
while current < (generation + 1) * self.num_procs {
std::thread::sleep(std::time::Duration::from_millis(10));
current = self.count.load(Ordering::Relaxed);
}
}
}
#[test]
fn test_multi_process() {
// Initialize
let max_size = 1_000_000_000_000;
let init_struct = ShmemHandle::new("test_multi_process", 0, max_size).unwrap();
let ptr = init_struct.data_ptr.as_ptr();
// Store the SimpleBarrier in the first 1k of the area.
init_struct.set_size(10000).unwrap();
let barrier_ptr: *mut SimpleBarrier = unsafe {
ptr.add(ptr.align_offset(std::mem::align_of::<SimpleBarrier>()))
.cast()
};
unsafe { SimpleBarrier::init(barrier_ptr, 2) };
let barrier = unsafe { barrier_ptr.as_ref().unwrap() };
// Fork another test process. The code after this runs in both processes concurrently.
let fork_result = unsafe { nix::unistd::fork().unwrap() };
// In the parent, fill bytes between 1000..2000. In the child, between 2000..3000
if fork_result.is_parent() {
write_range(ptr, 0xAA, 1000..2000);
} else {
write_range(ptr, 0xBB, 2000..3000);
}
barrier.wait();
// Verify the contents. (in both processes)
assert_range(ptr, 0xAA, 1000..2000);
assert_range(ptr, 0xBB, 2000..3000);
// Grow, from the child this time
let size = 10_000_000;
if !fork_result.is_parent() {
init_struct.set_size(size).unwrap();
}
barrier.wait();
// make some writes at the end
if fork_result.is_parent() {
write_range(ptr, 0xAA, (size - 10)..size);
} else {
write_range(ptr, 0xBB, (size - 20)..(size - 10));
}
barrier.wait();
// Verify the contents. (This runs in both processes)
assert_range(ptr, 0, (size - 1000)..(size - 20));
assert_range(ptr, 0xBB, (size - 20)..(size - 10));
assert_range(ptr, 0xAA, (size - 10)..size);
if let ForkResult::Parent { child } = fork_result {
nix::sys::wait::waitpid(child, None).unwrap();
}
}
}
pub mod shmem;

409
libs/neon-shmem/src/shmem.rs Normal file
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@@ -0,0 +1,409 @@
//! Dynamically resizable contiguous chunk of shared memory
use std::num::NonZeroUsize;
use std::os::fd::{AsFd, BorrowedFd, OwnedFd};
use std::ptr::NonNull;
use std::sync::atomic::{AtomicUsize, Ordering};
use nix::errno::Errno;
use nix::sys::mman::MapFlags;
use nix::sys::mman::ProtFlags;
use nix::sys::mman::mmap as nix_mmap;
use nix::sys::mman::munmap as nix_munmap;
use nix::unistd::ftruncate as nix_ftruncate;
/// `ShmemHandle` represents a shared memory area that can be shared by processes over `fork()`.
/// Unlike shared memory allocated by Postgres, this area is resizable, up to `max_size` that's
/// specified at creation.
///
/// The area is backed by an anonymous file created with `memfd_create()`. The full address space for
/// `max_size` is reserved up-front with `mmap()`, but whenever you call [`ShmemHandle::set_size`],
/// the underlying file is resized. Do not access the area beyond the current size. Currently, that
/// will cause the file to be expanded, but we might use `mprotect()` etc. to enforce that in the
/// future.
pub struct ShmemHandle {
/// memfd file descriptor
fd: OwnedFd,
max_size: usize,
// Pointer to the beginning of the shared memory area. The header is stored there.
shared_ptr: NonNull<SharedStruct>,
// Pointer to the beginning of the user data
pub data_ptr: NonNull<u8>,
}
/// This is stored at the beginning in the shared memory area.
struct SharedStruct {
max_size: usize,
/// Current size of the backing file. The high-order bit is used for the [`RESIZE_IN_PROGRESS`] flag.
current_size: AtomicUsize,
}
const RESIZE_IN_PROGRESS: usize = 1 << 63;
const HEADER_SIZE: usize = std::mem::size_of::<SharedStruct>();
/// Error type returned by the [`ShmemHandle`] functions.
#[derive(thiserror::Error, Debug)]
#[error("{msg}: {errno}")]
pub struct Error {
pub msg: String,
pub errno: Errno,
}
impl Error {
fn new(msg: &str, errno: Errno) -> Self {
Self {
msg: msg.to_string(),
errno,
}
}
}
impl ShmemHandle {
/// Create a new shared memory area. To communicate between processes, the processes need to be
/// `fork()`'d after calling this, so that the `ShmemHandle` is inherited by all processes.
///
/// If the `ShmemHandle` is dropped, the memory is unmapped from the current process. Other
/// processes can continue using it, however.
pub fn new(name: &str, initial_size: usize, max_size: usize) -> Result<Self, Error> {
// create the backing anonymous file.
let fd = create_backing_file(name)?;
Self::new_with_fd(fd, initial_size, max_size)
}
fn new_with_fd(fd: OwnedFd, initial_size: usize, max_size: usize) -> Result<Self, Error> {
// We reserve the high-order bit for the `RESIZE_IN_PROGRESS` flag, and the actual size
// is a little larger than this because of the SharedStruct header. Make the upper limit
// somewhat smaller than that, because with anything close to that, you'll run out of
// memory anyway.
assert!(max_size < 1 << 48, "max size {max_size} too large");
assert!(
initial_size <= max_size,
"initial size {initial_size} larger than max size {max_size}"
);
// The actual initial / max size is the one given by the caller, plus the size of
// 'SharedStruct'.
let initial_size = HEADER_SIZE + initial_size;
let max_size = NonZeroUsize::new(HEADER_SIZE + max_size).unwrap();
// Reserve address space for it with mmap
//
// TODO: Use MAP_HUGETLB if possible
let start_ptr = unsafe {
nix_mmap(
None,
max_size,
ProtFlags::PROT_READ | ProtFlags::PROT_WRITE,
MapFlags::MAP_SHARED,
&fd,
0,
)
}
.map_err(|e| Error::new("mmap failed", e))?;
// Reserve space for the initial size
enlarge_file(fd.as_fd(), initial_size as u64)?;
// Initialize the header
let shared: NonNull<SharedStruct> = start_ptr.cast();
unsafe {
shared.write(SharedStruct {
max_size: max_size.into(),
current_size: AtomicUsize::new(initial_size),
});
}
// The user data begins after the header
let data_ptr = unsafe { start_ptr.cast().add(HEADER_SIZE) };
Ok(Self {
fd,
max_size: max_size.into(),
shared_ptr: shared,
data_ptr,
})
}
// return reference to the header
fn shared(&self) -> &SharedStruct {
unsafe { self.shared_ptr.as_ref() }
}
/// Resize the shared memory area. `new_size` must not be larger than the `max_size` specified
/// when creating the area.
///
/// This may only be called from one process/thread concurrently. We detect that case
/// and return an [`shmem::Error`](Error).
pub fn set_size(&self, new_size: usize) -> Result<(), Error> {
let new_size = new_size + HEADER_SIZE;
let shared = self.shared();
assert!(
new_size <= self.max_size,
"new size ({new_size}) is greater than max size ({})",
self.max_size
);
assert_eq!(self.max_size, shared.max_size);
// Lock the area by setting the bit in `current_size`
//
// Ordering::Relaxed would probably be sufficient here, as we don't access any other memory
// and the `posix_fallocate`/`ftruncate` call is surely a synchronization point anyway. But
// since this is not performance-critical, better safe than sorry.
let mut old_size = shared.current_size.load(Ordering::Acquire);
loop {
if (old_size & RESIZE_IN_PROGRESS) != 0 {
return Err(Error::new(
"concurrent resize detected",
Errno::UnknownErrno,
));
}
match shared.current_size.compare_exchange(
old_size,
new_size,
Ordering::Acquire,
Ordering::Relaxed,
) {
Ok(_) => break,
Err(x) => old_size = x,
}
}
// Ok, we got the lock.
//
// NB: If anything goes wrong, we *must* clear the bit!
let result = {
use std::cmp::Ordering::{Equal, Greater, Less};
match new_size.cmp(&old_size) {
Less => nix_ftruncate(&self.fd, new_size as i64)
.map_err(|e| Error::new("could not shrink shmem segment, ftruncate failed", e)),
Equal => Ok(()),
Greater => enlarge_file(self.fd.as_fd(), new_size as u64),
}
};
// Unlock
shared.current_size.store(
if result.is_ok() { new_size } else { old_size },
Ordering::Release,
);
result
}
/// Returns the current user-visible size of the shared memory segment.
///
/// NOTE: a concurrent [`ShmemHandle::set_size()`] call can change the size at any time.
/// It is the caller's responsibility not to access the area beyond the current size.
pub fn current_size(&self) -> usize {
let total_current_size =
self.shared().current_size.load(Ordering::Relaxed) & !RESIZE_IN_PROGRESS;
total_current_size - HEADER_SIZE
}
}
impl Drop for ShmemHandle {
fn drop(&mut self) {
// SAFETY: The pointer was obtained from mmap() with the given size.
// We unmap the entire region.
let _ = unsafe { nix_munmap(self.shared_ptr.cast(), self.max_size) };
// The fd is dropped automatically by OwnedFd.
}
}
/// Create a "backing file" for the shared memory area. On Linux, use `memfd_create()`, to create an
/// anonymous in-memory file. One macos, fall back to a regular file. That's good enough for
/// development and testing, but in production we want the file to stay in memory.
///
/// Disable unused variables warnings because `name` is unused in the macos path.
#[allow(unused_variables)]
fn create_backing_file(name: &str) -> Result<OwnedFd, Error> {
#[cfg(not(target_os = "macos"))]
{
nix::sys::memfd::memfd_create(name, nix::sys::memfd::MFdFlags::empty())
.map_err(|e| Error::new("memfd_create failed", e))
}
#[cfg(target_os = "macos")]
{
let file = tempfile::tempfile().map_err(|e| {
Error::new(
"could not create temporary file to back shmem area",
nix::errno::Errno::from_raw(e.raw_os_error().unwrap_or(0)),
)
})?;
Ok(OwnedFd::from(file))
}
}
fn enlarge_file(fd: BorrowedFd, size: u64) -> Result<(), Error> {
// Use posix_fallocate() to enlarge the file. It reserves the space correctly, so that
// we don't get a segfault later when trying to actually use it.
#[cfg(not(target_os = "macos"))]
{
nix::fcntl::posix_fallocate(fd, 0, size as i64)
.map_err(|e| Error::new("could not grow shmem segment, posix_fallocate failed", e))
}
// As a fallback on macos, which doesn't have posix_fallocate, use plain 'fallocate'
#[cfg(target_os = "macos")]
{
nix::unistd::ftruncate(fd, size as i64)
.map_err(|e| Error::new("could not grow shmem segment, ftruncate failed", e))
}
}
#[cfg(test)]
mod tests {
use super::*;
use nix::unistd::ForkResult;
use std::ops::Range;
/// check that all bytes in given range have the expected value.
fn assert_range(ptr: *const u8, expected: u8, range: Range<usize>) {
for i in range {
let b = unsafe { *(ptr.add(i)) };
assert_eq!(expected, b, "unexpected byte at offset {i}");
}
}
/// Write 'b' to all bytes in the given range
fn write_range(ptr: *mut u8, b: u8, range: Range<usize>) {
unsafe { std::ptr::write_bytes(ptr.add(range.start), b, range.end - range.start) };
}
// simple single-process test of growing and shrinking
#[test]
fn test_shmem_resize() -> Result<(), Error> {
let max_size = 1024 * 1024;
let init_struct = ShmemHandle::new("test_shmem_resize", 0, max_size)?;
assert_eq!(init_struct.current_size(), 0);
// Initial grow
let size1 = 10000;
init_struct.set_size(size1).unwrap();
assert_eq!(init_struct.current_size(), size1);
// Write some data
let data_ptr = init_struct.data_ptr.as_ptr();
write_range(data_ptr, 0xAA, 0..size1);
assert_range(data_ptr, 0xAA, 0..size1);
// Shrink
let size2 = 5000;
init_struct.set_size(size2).unwrap();
assert_eq!(init_struct.current_size(), size2);
// Grow again
let size3 = 20000;
init_struct.set_size(size3).unwrap();
assert_eq!(init_struct.current_size(), size3);
// Try to read it. The area that was shrunk and grown again should read as all zeros now
assert_range(data_ptr, 0xAA, 0..5000);
assert_range(data_ptr, 0, 5000..size1);
// Try to grow beyond max_size
//let size4 = max_size + 1;
//assert!(init_struct.set_size(size4).is_err());
// Dropping init_struct should unmap the memory
drop(init_struct);
Ok(())
}
/// This is used in tests to coordinate between test processes. It's like `std::sync::Barrier`,
/// but is stored in the shared memory area and works across processes. It's implemented by
/// polling, because e.g. standard rust mutexes are not guaranteed to work across processes.
struct SimpleBarrier {
num_procs: usize,
count: AtomicUsize,
}
impl SimpleBarrier {
unsafe fn init(ptr: *mut SimpleBarrier, num_procs: usize) {
unsafe {
*ptr = SimpleBarrier {
num_procs,
count: AtomicUsize::new(0),
}
}
}
pub fn wait(&self) {
let old = self.count.fetch_add(1, Ordering::Relaxed);
let generation = old / self.num_procs;
let mut current = old + 1;
while current < (generation + 1) * self.num_procs {
std::thread::sleep(std::time::Duration::from_millis(10));
current = self.count.load(Ordering::Relaxed);
}
}
}
#[test]
fn test_multi_process() {
// Initialize
let max_size = 1_000_000_000_000;
let init_struct = ShmemHandle::new("test_multi_process", 0, max_size).unwrap();
let ptr = init_struct.data_ptr.as_ptr();
// Store the SimpleBarrier in the first 1k of the area.
init_struct.set_size(10000).unwrap();
let barrier_ptr: *mut SimpleBarrier = unsafe {
ptr.add(ptr.align_offset(std::mem::align_of::<SimpleBarrier>()))
.cast()
};
unsafe { SimpleBarrier::init(barrier_ptr, 2) };
let barrier = unsafe { barrier_ptr.as_ref().unwrap() };
// Fork another test process. The code after this runs in both processes concurrently.
let fork_result = unsafe { nix::unistd::fork().unwrap() };
// In the parent, fill bytes between 1000..2000. In the child, between 2000..3000
if fork_result.is_parent() {
write_range(ptr, 0xAA, 1000..2000);
} else {
write_range(ptr, 0xBB, 2000..3000);
}
barrier.wait();
// Verify the contents. (in both processes)
assert_range(ptr, 0xAA, 1000..2000);
assert_range(ptr, 0xBB, 2000..3000);
// Grow, from the child this time
let size = 10_000_000;
if !fork_result.is_parent() {
init_struct.set_size(size).unwrap();
}
barrier.wait();
// make some writes at the end
if fork_result.is_parent() {
write_range(ptr, 0xAA, (size - 10)..size);
} else {
write_range(ptr, 0xBB, (size - 20)..(size - 10));
}
barrier.wait();
// Verify the contents. (This runs in both processes)
assert_range(ptr, 0, (size - 1000)..(size - 20));
assert_range(ptr, 0xBB, (size - 20)..(size - 10));
assert_range(ptr, 0xAA, (size - 10)..size);
if let ForkResult::Parent { child } = fork_result {
nix::sys::wait::waitpid(child, None).unwrap();
}
}
}