RD-5: Implemented Rust equivalent zone allocator

README.md

@@ -1,7 +1,7 @@
 # RustyDoom
 
-A Rust version of the original DOOM from the offically released source code found at [https://github.com/id-software/doom](https://github.com/id-software/doom)
+A Rust version of the original DOOM base on the offically released source code found at [https://github.com/id-software/doom](https://github.com/id-software/doom)
 
-This is more of a learning exercise than something good!
+This is more of a learning exercise than something good! For example, the original `z_zone.c` and `z_zone.h` will be more "Rust-like" compared to the original version.
 
 This repository will only contain the SHAREWARE verison of the original DOOM1, but will be able to run both IWAD and PWADS.

src/main.rs

@@ -7,6 +7,7 @@ mod m_argv;
 mod m_misc;
 mod v_video;
 mod w_wad;
+mod z_zone;
 mod math;
 
 

src/z_zone/mod.rs

@@ -0,0 +1,165 @@
+/// Memory allocator stuff
+/// Compared to the original source, this will be some what "lean n' mean"
+use std::cell::RefCell;
+use std::collections::HashMap;
+
+#[derive(Debug, Clone, Copy, PartialEq, PartialOrd)]
+/// The PurgeTags (PUs)
+/// Tags < 100 are not overwritten untill freed
+pub enum PurgeTag {
+    /// Static the entire execution time
+    Static = 1,
+    /// Static while playing
+    Sound = 2,
+    /// static while playing
+    Music = 3,
+    /// Original source comment: anything else dave wants static
+    Dave = 4,
+    /// static until level exit
+    Level = 50,
+    /// static for special thinkers in a level
+    LevSpec = 51,
+    // Tags >= 100 are "purgable" whenever needed
+    PurgeLevel = 100,
+    Cache = 101,
+}
+
+
+/// Provides metadata on 
+struct AllocMeta {
+    /// The size of the allocation
+    size: usize,
+    /// The PU tag associated with the allocation
+    tag: i32,
+    /// A pointer to the caller's tracking pointer, cleared automatically upon freeing
+    user: *mut *mut u8,
+}
+
+
+thread_local! {
+    // We promise not to be naughty and access this from another thread :)
+    /// Mapping from pointers (as usize) to the correspond AllocationMeta
+    static REGISTRY: RefCell<HashMap<usize, AllocMeta>> = RefCell::new(HashMap::new());
+}
+
+// Helper method that we can use to access the registry
+fn with_registry<F, R>(f: F) -> R 
+where
+    F: FnOnce(&mut HashMap<usize, AllocMeta>) -> R
+{
+    REGISTRY.with(|registry| f(&mut *registry.borrow_mut()))
+}
+
+#[allow(non_snake_case)]
+/// Initalized the Zone memory allocator sub-system
+pub fn Z_Init() {
+    // do nothing, we get lazy init of the registry.
+}
+
+#[allow(non_snake_case)]
+/// Allocate a contiguous chunk of zeroed memory from the zone allocator
+/// # Safety
+/// This function returns a raw pointer that bypasses Rust's automatic memory 
+/// tracking. The returned memory must be manually reclaimed using `Z_Free`.
+pub unsafe fn Z_Malloc(size: usize, tag: i32, user: *mut *mut u8) -> *mut u8 {
+    let mut buffer = vec![0u8; size];
+    let ptr = buffer.as_mut_ptr();
+
+    // ensures Rust does not drop the buffer at the end of this block
+    std::mem::forget(buffer);
+
+    // Update the engine's tracking pointer if one was provided
+    if !user.is_null() {
+        unsafe {
+            *user = ptr;
+        }
+    }
+
+    // Save allocation details using the pointer address as the key
+    with_registry(|map| {
+        map.insert(ptr as usize, AllocMeta { size, tag, user });
+    });
+
+    ptr
+}
+
+#[allow(non_snake_case)]
+/// Reclaims and frees a allocation from Z_Malloc
+/// # Safety
+/// The provided pointer must point to a valid allocation tracked by the registry.
+/// Passing an invalid or already freed pointer can result in undefined behavior
+pub unsafe fn Z_Free(ptr: *mut u8) {
+    if ptr.is_null() {
+        return;
+    }
+    let removed = with_registry(|map| map.remove(&(ptr as usize)));
+    
+    if let Some(meta) = removed {
+        // Clear the caller's tracking pointer to prevent use-after-free
+        if !meta.user.is_null() {
+            unsafe {
+                *meta.user = std::ptr::null_mut();
+            }
+        }
+        // re-build the vector so Rust can drop it
+        unsafe {
+            let _dropped_vec = Vec::from_raw_parts(ptr, meta.size, meta.size);
+        }
+    }
+}
+
+#[allow(non_snake_case)]
+/// Frees all memory allocations between the specific lifetime PU tags.
+/// # Safety
+/// All pointers tracked within this tag boundary are invalidated and deallocate
+pub unsafe fn Z_FreeTags(low_tag: i32, high_tag: i32) {
+
+    // get all of the allocations to free
+    let tags_to_free: Vec<usize> = with_registry(|map| {
+        map.iter()
+            .filter(|(_, meta)| meta.tag >= low_tag && meta.tag <= high_tag)
+            .map(|(ptr_addr,_)| *ptr_addr)
+            .collect()
+    });
+
+    // remove each pointer returned from the map and drop the memory
+
+    for ptr_addr in tags_to_free {
+        let removed_ptr = with_registry(|map| map.remove(&ptr_addr));
+
+        if let Some(meta) = removed_ptr {
+            let p = ptr_addr as *mut u8;
+            unsafe {
+                // clear caller tracking pointer to preven use after free
+                if !meta.user.is_null() {
+                    *meta.user = std::ptr::null_mut();
+                }
+
+                let _dropped_vec = Vec::from_raw_parts(p, meta.size, meta.size);
+            }
+        }
+    }
+}
+
+// Internal ChangeTag function
+#[allow(non_snake_case)]
+fn Z_ChangeTagInternal(ptr: *mut u8, tag: i32) {
+    if ptr.is_null() {
+        return;
+    }
+
+    with_registry(|map| {
+        if let Some(meta) = map.get_mut(&(ptr as usize)) {
+            meta.tag = tag;
+        }
+    })
+}
+/// Modifies the lifetime tag of an active allocation.
+/// 
+/// # Safety
+/// The provided pointer must point to a valid allocation tracked by the registry
+#[allow(non_snake_case)]
+pub unsafe fn Z_ChangeTag(ptr: *mut u8, tag: i32) {
+    // removes the original helper macro from the original C, we don't need withcraft here
+    Z_ChangeTagInternal(ptr, tag);
+}