adopt some SHM data structures to support NPO (needed as elegant way …

…to equalize some data structure sizes in zenoh-c)

commons/zenoh-codec/src/core/shm.rs

@@ -11,6 +11,8 @@
 // Contributors:
 //   ZettaScale Zenoh Team, <[email protected]>
 //
+use std::num::NonZeroUsize;
+
 use zenoh_buffers::{
     reader::{DidntRead, Reader},
     writer::{DidntWrite, Writer},
@@ -62,6 +64,18 @@ where
     }
 }
 
+impl<W> WCodec<NonZeroUsize, &mut W> for Zenoh080
+where
+    W: Writer,
+{
+    type Output = Result<(), DidntWrite>;
+
+    fn write(self, writer: &mut W, x: NonZeroUsize) -> Self::Output {
+        self.write(&mut *writer, x.get())?;
+        Ok(())
+    }
+}
+
 impl<W> WCodec<&ShmBufInfo, &mut W> for Zenoh080
 where
     W: Writer,
@@ -80,7 +94,7 @@ where
 
         self.write(&mut *writer, data_descriptor)?;
         self.write(&mut *writer, shm_protocol)?;
-        self.write(&mut *writer, data_len)?;
+        self.write(&mut *writer, *data_len)?;
         self.write(&mut *writer, watchdog_descriptor)?;
         self.write(&mut *writer, header_descriptor)?;
         self.write(&mut *writer, generation)?;
@@ -138,6 +152,19 @@ where
     }
 }
 
+impl<R> RCodec<NonZeroUsize, &mut R> for Zenoh080
+where
+    R: Reader,
+{
+    type Error = DidntRead;
+
+    fn read(self, reader: &mut R) -> Result<NonZeroUsize, Self::Error> {
+        let size: usize = self.read(&mut *reader)?;
+        let size = NonZeroUsize::new(size).ok_or(DidntRead)?;
+        Ok(size)
+    }
+}
+
 impl<R> RCodec<ShmBufInfo, &mut R> for Zenoh080
 where
     R: Reader,

commons/zenoh-shm/Cargo.toml

@@ -52,4 +52,4 @@ lockfree = { workspace = true }
 stabby = { workspace = true }
 
 [dev-dependencies]
-libc = { workspace = true }
+libc = { workspace = true }

commons/zenoh-shm/src/api/protocol_implementations/posix/posix_shm_provider_backend.rs

@@ -16,6 +16,7 @@ use std::{
     borrow::Borrow,
     cmp,
     collections::BinaryHeap,
+    num::NonZeroUsize,
     sync::{
         atomic::{AtomicPtr, AtomicUsize, Ordering},
         Mutex,
@@ -31,7 +32,7 @@ use crate::api::{
     provider::{
         chunk::{AllocatedChunk, ChunkDescriptor},
         shm_provider_backend::ShmProviderBackend,
-        types::{AllocAlignment, ChunkAllocResult, MemoryLayout, ZAllocError},
+        types::{AllocAlignment, ChunkAllocResult, MemoryLayout, ZAllocError, ZLayoutError},
     },
 };
 
@@ -45,7 +46,7 @@ const MIN_FREE_CHUNK_SIZE: usize = 1_024;
 #[derive(Eq, Copy, Clone, Debug)]
 struct Chunk {
     offset: ChunkID,
-    size: usize,
+    size: NonZeroUsize,
 }
 
 impl Ord for Chunk {
@@ -86,8 +87,12 @@ impl PosixShmProviderBackendBuilder {
         self,
         size: usize,
         alignment: AllocAlignment,
-    ) -> ZResult<LayoutedPosixShmProviderBackendBuilder<MemoryLayout>> {
-        let layout = MemoryLayout::new(size, alignment)?;
+    ) -> Result<LayoutedPosixShmProviderBackendBuilder<MemoryLayout>, ZLayoutError> {
+        let layout = MemoryLayout::new(
+            size.try_into()
+                .map_err(|_| ZLayoutError::IncorrectLayoutArgs)?,
+            alignment,
+        )?;
         Ok(LayoutedPosixShmProviderBackendBuilder { layout })
     }
 
@@ -96,8 +101,12 @@ impl PosixShmProviderBackendBuilder {
     pub fn with_size(
         self,
         size: usize,
-    ) -> ZResult<LayoutedPosixShmProviderBackendBuilder<MemoryLayout>> {
-        let layout = MemoryLayout::new(size, AllocAlignment::default())?;
+    ) -> Result<LayoutedPosixShmProviderBackendBuilder<MemoryLayout>, ZLayoutError> {
+        let layout = MemoryLayout::new(
+            size.try_into()
+                .map_err(|_| ZLayoutError::IncorrectLayoutArgs)?,
+            AllocAlignment::default(),
+        )?;
         Ok(LayoutedPosixShmProviderBackendBuilder { layout })
     }
 }
@@ -149,7 +158,7 @@ impl PosixShmProviderBackend {
         );
 
         Ok(Self {
-            available: AtomicUsize::new(layout.size()),
+            available: AtomicUsize::new(layout.size().get()),
             segment,
             free_list: Mutex::new(free_list),
             alignment: layout.alignment(),
@@ -163,7 +172,7 @@ impl ShmProviderBackend for PosixShmProviderBackend {
 
         let required_len = layout.size();
 
-        if self.available.load(Ordering::Relaxed) < required_len {
+        if self.available.load(Ordering::Relaxed) < required_len.get() {
             tracing::trace!( "PosixShmProviderBackend does not have sufficient free memory to allocate {:?}, try de-fragmenting!", layout);
             return Err(ZAllocError::OutOfMemory);
         }
@@ -176,16 +185,20 @@ impl ShmProviderBackend for PosixShmProviderBackend {
             Some(mut chunk) if chunk.size >= required_len => {
                 // NOTE: don't loose any chunks here, as it will lead to memory leak
                 tracing::trace!("Allocator selected Chunk ({:?})", &chunk);
-                if chunk.size - required_len >= MIN_FREE_CHUNK_SIZE {
+                if chunk.size.get() - required_len.get() >= MIN_FREE_CHUNK_SIZE {
                     let free_chunk = Chunk {
-                        offset: chunk.offset + required_len as ChunkID,
-                        size: chunk.size - required_len,
+                        offset: chunk.offset + required_len.get() as ChunkID,
+                        // SAFETY: this is safe because we always operate on a leftover, which is checked above!
+                        size: unsafe {
+                            NonZeroUsize::new_unchecked(chunk.size.get() - required_len.get())
+                        },
                     };
                     tracing::trace!("The allocation will leave a Free Chunk: {:?}", &free_chunk);
                     guard.push(free_chunk);
                     chunk.size = required_len;
                 }
-                self.available.fetch_sub(chunk.size, Ordering::Relaxed);
+                self.available
+                    .fetch_sub(chunk.size.get(), Ordering::Relaxed);
 
                 let descriptor =
                     ChunkDescriptor::new(self.segment.segment.id(), chunk.offset, chunk.size);
@@ -219,16 +232,18 @@ impl ShmProviderBackend for PosixShmProviderBackend {
             offset: chunk.chunk,
             size: chunk.len,
         };
-        self.available.fetch_add(free_chunk.size, Ordering::Relaxed);
+        self.available
+            .fetch_add(free_chunk.size.get(), Ordering::Relaxed);
         zlock!(self.free_list).push(free_chunk);
     }
 
     fn defragment(&self) -> usize {
         fn try_merge_adjacent_chunks(a: &Chunk, b: &Chunk) -> Option<Chunk> {
-            let end_offset = a.offset as usize + a.size;
+            let end_offset = a.offset as usize + a.size.get();
             if end_offset == b.offset as usize {
                 Some(Chunk {
-                    size: a.size + b.size,
+                    // SAFETY: this is safe because we operate on non-zero sizes and it will never overflow
+                    size: unsafe { NonZeroUsize::new_unchecked(a.size.get() + b.size.get()) },
                     offset: a.offset,
                 })
             } else {
@@ -256,7 +271,7 @@ impl ShmProviderBackend for PosixShmProviderBackend {
                 match try_merge_adjacent_chunks(&current, &next) {
                     Some(c) => {
                         current = c;
-                        largest = largest.max(current.size);
+                        largest = largest.max(current.size.get());
                         if i == n {
                             guard.push(current)
                         }
@@ -279,7 +294,7 @@ impl ShmProviderBackend for PosixShmProviderBackend {
         self.available.load(Ordering::Relaxed)
     }
 
-    fn layout_for(&self, layout: MemoryLayout) -> ZResult<MemoryLayout> {
+    fn layout_for(&self, layout: MemoryLayout) -> Result<MemoryLayout, ZLayoutError> {
         layout.extend(self.alignment)
     }
 }

commons/zenoh-shm/src/api/protocol_implementations/posix/posix_shm_segment.rs

@@ -12,7 +12,7 @@
 //   ZettaScale Zenoh Team, <[email protected]>
 //
 
-use std::sync::atomic::AtomicPtr;
+use std::{num::NonZeroUsize, sync::atomic::AtomicPtr};
 
 use zenoh_result::ZResult;
 
@@ -32,8 +32,8 @@ pub(crate) struct PosixShmSegment {
 }
 
 impl PosixShmSegment {
-    pub(crate) fn create(alloc_size: usize) -> ZResult<Self> {
-        let segment = ArrayInSHM::create(alloc_size, POSIX_SHM_SEGMENT_PREFIX)?;
+    pub(crate) fn create(alloc_size: NonZeroUsize) -> ZResult<Self> {
+        let segment = ArrayInSHM::create(alloc_size.get(), POSIX_SHM_SEGMENT_PREFIX)?;
         Ok(Self { segment })
     }
 

commons/zenoh-shm/src/api/provider/chunk.rs

@@ -12,7 +12,7 @@
 //   ZettaScale Zenoh Team, <[email protected]>
 //
 
-use std::sync::atomic::AtomicPtr;
+use std::{num::NonZeroUsize, sync::atomic::AtomicPtr};
 
 use crate::api::common::types::{ChunkID, SegmentID};
 
@@ -22,13 +22,13 @@ use crate::api::common::types::{ChunkID, SegmentID};
 pub struct ChunkDescriptor {
     pub segment: SegmentID,
     pub chunk: ChunkID,
-    pub len: usize,
+    pub len: NonZeroUsize,
 }
 
 impl ChunkDescriptor {
     /// Create a new Chunk Descriptor
     #[zenoh_macros::unstable_doc]
-    pub fn new(segment: SegmentID, chunk: ChunkID, len: usize) -> Self {
+    pub fn new(segment: SegmentID, chunk: ChunkID, len: NonZeroUsize) -> Self {
         Self {
             segment,
             chunk,

commons/zenoh-shm/src/api/provider/shm_provider.rs

@@ -16,6 +16,7 @@ use std::{
     collections::VecDeque,
     future::{Future, IntoFuture},
     marker::PhantomData,
+    num::NonZeroUsize,
     pin::Pin,
     sync::{atomic::Ordering, Arc, Mutex},
     time::Duration,
@@ -159,7 +160,7 @@ where
     IDSource: ProtocolIDSource,
     Backend: ShmProviderBackend,
 {
-    size: usize,
+    size: NonZeroUsize,
     provider_layout: MemoryLayout,
     provider: &'a ShmProvider<IDSource, Backend>,
 }
@@ -182,8 +183,14 @@ where
         // NOTE: Depending on internal implementation, provider's backend might relayout
         // the allocations for bigger alignment (ex. 4-byte aligned allocation to 8-bytes aligned)
 
+        // Obtain nonzero size
+        let nonzero_size = data
+            .size
+            .try_into()
+            .map_err(|_| ZLayoutError::IncorrectLayoutArgs)?;
+
         // Create layout for specified arguments
-        let layout = MemoryLayout::new(data.size, data.alignment)
+        let layout = MemoryLayout::new(nonzero_size, data.alignment)
             .map_err(|_| ZLayoutError::IncorrectLayoutArgs)?;
 
         // Obtain provider's layout for our layout
@@ -194,7 +201,7 @@ where
             .map_err(|_| ZLayoutError::ProviderIncompatibleLayout)?;
 
         Ok(Self {
-            size: data.size,
+            size: nonzero_size,
             provider_layout,
             provider: data.provider,
         })
@@ -320,7 +327,7 @@ where
         let result = InnerPolicy::alloc(layout, provider);
         if let Err(ZAllocError::OutOfMemory) = result {
             // try to alloc again only if GC managed to reclaim big enough chunk
-            if provider.garbage_collect() >= layout.size() {
+            if provider.garbage_collect() >= layout.size().get() {
                 return AltPolicy::alloc(layout, provider);
             }
         }
@@ -352,7 +359,7 @@ where
         let result = InnerPolicy::alloc(layout, provider);
         if let Err(ZAllocError::NeedDefragment) = result {
             // try to alloc again only if big enough chunk was defragmented
-            if provider.defragment() >= layout.size() {
+            if provider.defragment() >= layout.size().get() {
                 return AltPolicy::alloc(layout, provider);
             }
         }
@@ -803,6 +810,8 @@ where
     /// Remember that chunk's len may be >= len!
     #[zenoh_macros::unstable_doc]
     pub fn map(&self, chunk: AllocatedChunk, len: usize) -> ZResult<ZShmMut> {
+        let len = len.try_into()?;
+
         // allocate resources for SHM buffer
         let (allocated_header, allocated_watchdog, confirmed_watchdog) = Self::alloc_resources()?;
 
@@ -837,7 +846,7 @@ where
             if is_free_chunk(maybe_free) {
                 tracing::trace!("Garbage Collecting Chunk: {:?}", maybe_free);
                 self.backend.free(&maybe_free.descriptor);
-                largest = largest.max(maybe_free.descriptor.len);
+                largest = largest.max(maybe_free.descriptor.len.get());
                 return false;
             }
             true
@@ -868,7 +877,7 @@ where
         }
     }
 
-    fn alloc_inner<Policy>(&self, size: usize, layout: &MemoryLayout) -> BufAllocResult
+    fn alloc_inner<Policy>(&self, size: NonZeroUsize, layout: &MemoryLayout) -> BufAllocResult
     where
         Policy: AllocPolicy,
     {
@@ -914,7 +923,7 @@ where
     fn wrap(
         &self,
         chunk: AllocatedChunk,
-        len: usize,
+        len: NonZeroUsize,
         allocated_header: AllocatedHeaderDescriptor,
         allocated_watchdog: AllocatedWatchdog,
         confirmed_watchdog: ConfirmedDescriptor,
@@ -971,7 +980,7 @@ where
 {
     async fn alloc_inner_async<Policy>(
         &self,
-        size: usize,
+        size: NonZeroUsize,
         backend_layout: &MemoryLayout,
     ) -> BufAllocResult
     where

commons/zenoh-shm/src/api/provider/shm_provider_backend.rs

@@ -11,12 +11,9 @@
 // Contributors:
 //   ZettaScale Zenoh Team, <[email protected]>
 //
-
-use zenoh_result::ZResult;
-
 use super::{
     chunk::ChunkDescriptor,
-    types::{ChunkAllocResult, MemoryLayout},
+    types::{ChunkAllocResult, MemoryLayout, ZLayoutError},
 };
 
 /// The provider backend trait
@@ -48,5 +45,5 @@ pub trait ShmProviderBackend {
     /// - validate, if the provided layout can be used with this backend
     /// - adopt the layout for backend capabilities
     #[zenoh_macros::unstable_doc]
-    fn layout_for(&self, layout: MemoryLayout) -> ZResult<MemoryLayout>;
+    fn layout_for(&self, layout: MemoryLayout) -> Result<MemoryLayout, ZLayoutError>;
 }