♻️ Remove Mutex from mem buffer (#9479)

render-wasm/src/mem.rs

@@ -1,61 +1,73 @@
-use std::sync::Mutex;
-
-use crate::error::{Error, Result, CRITICAL_ERROR};
+use crate::{error::Result, performance};
 
 pub const LAYOUT_ALIGN: usize = 4;
 
-pub static BUFFERU8: Mutex<Option<Vec<u8>>> = Mutex::new(None);
-pub static BUFFER_ERROR: Mutex<u8> = Mutex::new(0x00);
+// Please, read about the #[allow(static_mut_refs)]
+//
+// If we don't put this allow, the compiler shows a warning like this:
+//
+// shared references to mutable statics are dangerous; it's undefined behavior
+// if the static is mutated or if a mutable reference is created for it while
+// the shared reference lives
+//
+// https://doc.rust-lang.org/edition-guide/rust-2024/static-mut-references.html
+//
+// But this isn't a problem in a single-threaded environment like WebAssembly
+// because access/modification is always sequential, not parallel.
+pub static mut BUFFERU8: Option<Vec<u8>> = None;
+pub static mut BUFFER_ERROR: u8 = 0x00;
 
 pub fn clear_error_code() {
-    let mut guard = BUFFER_ERROR.lock().unwrap();
-    *guard = 0x00;
+    unsafe {
+        BUFFER_ERROR = 0x00;
+    }
 }
 
 /// Sets the error buffer from a byte. Used by #[wasm_error] when E: Into<u8>.
 pub fn set_error_code(code: u8) {
-    let mut guard = BUFFER_ERROR.lock().unwrap();
-    *guard = code;
+    unsafe {
+        BUFFER_ERROR = code;
+    }
 }
 
 #[no_mangle]
 pub extern "C" fn read_error_code() -> u8 {
-    if let Ok(guard) = BUFFER_ERROR.lock() {
-        *guard
-    } else {
-        CRITICAL_ERROR
-    }
+    unsafe { BUFFER_ERROR }
 }
 
 pub fn write_bytes(mut bytes: Vec<u8>) -> *mut u8 {
-    let mut guard = BUFFERU8.lock().unwrap();
+    unsafe {
+        performance::begin_measure!("write_bytes");
+        #[allow(static_mut_refs)]
+        if BUFFERU8.is_some() {
+            panic!("Bytes already allocated");
+        }
 
-    if guard.is_some() {
-        panic!("Bytes already allocated");
+        let ptr = bytes.as_mut_ptr();
+        BUFFERU8 = Some(bytes);
+        performance::end_measure!("write_bytes");
+        ptr
     }
-
-    let ptr = bytes.as_mut_ptr();
-
-    *guard = Some(bytes);
-    ptr
 }
 
 pub fn bytes() -> Vec<u8> {
-    let mut guard = BUFFERU8.lock().unwrap();
-    guard.take().expect("Buffer is not initialized")
+    unsafe {
+        #[allow(static_mut_refs)]
+        BUFFERU8.take().expect("Buffer is not initialized")
+    }
 }
 
 pub fn bytes_or_empty() -> Vec<u8> {
-    let mut guard = BUFFERU8.lock().unwrap();
-    guard.take().unwrap_or_default()
+    unsafe {
+        #[allow(static_mut_refs)]
+        BUFFERU8.take().unwrap_or_default()
+    }
 }
 
 pub fn free_bytes() -> Result<()> {
-    let mut guard = BUFFERU8
-        .lock()
-        .map_err(|_| Error::CriticalError("Failed to lock buffer".to_string()))?;
-    *guard = None;
-    std::mem::drop(guard);
+    unsafe {
+        BUFFERU8 = None;
+    }
     Ok(())
 }
 

render-wasm/src/wasm/mem.rs

@@ -9,15 +9,22 @@ use macros::wasm_error;
 #[no_mangle]
 #[wasm_error]
 pub extern "C" fn alloc_bytes(len: usize) -> Result<*mut u8> {
-    let mut guard = BUFFERU8
-        .lock()
-        .map_err(|_| Error::CriticalError("Failed to lock buffer".to_string()))?;
-
-    if guard.is_some() {
-        return Err(Error::CriticalError("Bytes already allocated".to_string()));
-    }
-
     unsafe {
+        // If we don't put this allow, the compiler shows a warning like this:
+        //
+        // shared references to mutable statics are dangerous; it's undefined behavior
+        // if the static is mutated or if a mutable reference is created for it while
+        // the shared reference lives
+        //
+        // https://doc.rust-lang.org/edition-guide/rust-2024/static-mut-references.html
+        //
+        // But this isn't a problem in a single-threaded environment like WebAssembly
+        // because access/modification is always sequential, not parallel.
+        #[allow(static_mut_refs)]
+        if BUFFERU8.is_some() {
+            return Err(Error::CriticalError("Bytes already allocated".to_string()));
+        }
+
         let layout = Layout::from_size_align_unchecked(len, LAYOUT_ALIGN);
         let ptr = alloc(layout);
         if ptr.is_null() {
@@ -25,7 +32,7 @@ pub extern "C" fn alloc_bytes(len: usize) -> Result<*mut u8> {
         }
         // TODO: Maybe this could be removed.
         ptr::write_bytes(ptr, 0, len);
-        *guard = Some(Vec::from_raw_parts(ptr, len, len));
+        BUFFERU8 = Some(Vec::from_raw_parts(ptr, len, len));
         Ok(ptr)
     }
 }