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2026-03-04 00:08:42 +00:00
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+// Copyright (c) 2024 RustyTorch Team
+// Licensed under MIT OR Apache-2.0
+//! GPU Backend Abstraction for CFD Operations
+//!
+//! This module provides a backend-agnostic interface for GPU-accelerated CFD kernels,
+//! supporting both CUDA (NVIDIA) and Metal (Apple Silicon) backends.
+//!
+//! # Architecture
+//!
+//! ```text
+//! GpuBackend trait
+//! ├── CudaBackend  (NVIDIA GPUs via cudarc)
+//! └── MetalBackend (Apple Silicon via rtx-metal)
+//! ```
+//!
+//! # Example
+//!
+//! ```rust,ignore
+//! let backend = GpuBackend::auto_detect()?;
+//! let buffer = backend.allocate::<f32>(1024)?;
+//! backend.launch_kernel("poisson_jacobi", config, &[buffer])?;
+//! ```
+
+use crate::error::CfdResult;
+use std::sync::Arc;
+
+/// Configuration for kernel launches
+#[derive(Debug, Clone)]
+pub struct LaunchConfig {
+    /// Grid dimensions (width, height, depth)
+    pub grid: (usize, usize, usize),
+    /// Thread group / block dimensions
+    pub block: (usize, usize, usize),
+    /// Shared memory size in bytes
+    pub shared_memory: usize,
+}
+
+impl LaunchConfig {
+    /// Create a 1D launch configuration
+    pub fn new_1d(n: usize, block_size: usize) -> Self {
+        let grid = (n + block_size - 1) / block_size;
+        Self {
+            grid: (grid, 1, 1),
+            block: (block_size, 1, 1),
+            shared_memory: 0,
+        }
+    }
+
+    /// Create a 2D launch configuration
+    pub fn new_2d(nx: usize, ny: usize, block_x: usize, block_y: usize) -> Self {
+        let grid_x = (nx + block_x - 1) / block_x;
+        let grid_y = (ny + block_y - 1) / block_y;
+        Self {
+            grid: (grid_x, grid_y, 1),
+            block: (block_x, block_y, 1),
+            shared_memory: 0,
+        }
+    }
+
+    /// Create a 3D launch configuration
+    pub fn new_3d(
+        nx: usize,
+        ny: usize,
+        nz: usize,
+        block_x: usize,
+        block_y: usize,
+        block_z: usize,
+    ) -> Self {
+        let grid_x = (nx + block_x - 1) / block_x;
+        let grid_y = (ny + block_y - 1) / block_y;
+        let grid_z = (nz + block_z - 1) / block_z;
+        Self {
+            grid: (grid_x, grid_y, grid_z),
+            block: (block_x, block_y, block_z),
+            shared_memory: 0,
+        }
+    }
+
+    /// Set shared memory size
+    pub fn with_shared_memory(mut self, size: usize) -> Self {
+        self.shared_memory = size;
+        self
+    }
+}
+
+/// GPU buffer handle - opaque type for backend-specific storage
+pub struct GpuBuffer {
+    /// Buffer ID for the backend
+    pub id: usize,
+    /// Size in elements
+    pub len: usize,
+    /// Element size in bytes
+    pub element_size: usize,
+}
+
+impl GpuBuffer {
+    /// Get total size in bytes
+    pub fn size_bytes(&self) -> usize {
+        self.len * self.element_size
+    }
+}
+
+/// Backend type enumeration
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum BackendType {
+    /// NVIDIA CUDA backend
+    Cuda,
+    /// Apple Metal backend
+    Metal,
+    /// CPU fallback
+    Cpu,
+}
+
+impl std::fmt::Display for BackendType {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            BackendType::Cuda => write!(f, "CUDA"),
+            BackendType::Metal => write!(f, "Metal"),
+            BackendType::Cpu => write!(f, "CPU"),
+        }
+    }
+}
+
+/// GPU Backend trait for CFD operations
+///
+/// This trait abstracts the underlying GPU framework (CUDA/Metal),
+/// providing a unified interface for CFD kernel execution.
+pub trait GpuBackend: Send + Sync {
+    /// Get the backend type
+    fn backend_type(&self) -> BackendType;
+
+    /// Get device name
+    fn device_name(&self) -> &str;
+
+    /// Check if backend is available
+    fn is_available(&self) -> bool;
+
+    /// Allocate a buffer on the device
+    fn allocate(&self, len: usize, element_size: usize) -> CfdResult<GpuBuffer>;
+
+    /// Free a buffer
+    fn free(&self, buffer: &GpuBuffer) -> CfdResult<()>;
+
+    /// Copy data from host to device
+    fn copy_to_device(&self, buffer: &GpuBuffer, data: &[u8]) -> CfdResult<()>;
+
+    /// Copy data from device to host
+    fn copy_to_host(&self, buffer: &GpuBuffer, data: &mut [u8]) -> CfdResult<()>;
+
+    /// Synchronize all pending operations
+    fn synchronize(&self) -> CfdResult<()>;
+
+    /// Get maximum threads per block/threadgroup
+    fn max_threads_per_block(&self) -> usize;
+
+    /// Get device memory size in bytes
+    fn device_memory(&self) -> usize;
+}
+
+/// CPU fallback backend for testing and non-GPU systems
+pub struct CpuBackend {
+    name: String,
+}
+
+impl CpuBackend {
+    /// Create a new CPU backend
+    pub fn new() -> Self {
+        Self {
+            name: "CPU".to_string(),
+        }
+    }
+}
+
+impl Default for CpuBackend {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl GpuBackend for CpuBackend {
+    fn backend_type(&self) -> BackendType {
+        BackendType::Cpu
+    }
+
+    fn device_name(&self) -> &str {
+        &self.name
+    }
+
+    fn is_available(&self) -> bool {
+        true
+    }
+
+    fn allocate(&self, len: usize, element_size: usize) -> CfdResult<GpuBuffer> {
+        Ok(GpuBuffer {
+            id: 0,
+            len,
+            element_size,
+        })
+    }
+
+    fn free(&self, _buffer: &GpuBuffer) -> CfdResult<()> {
+        Ok(())
+    }
+
+    fn copy_to_device(&self, _buffer: &GpuBuffer, _data: &[u8]) -> CfdResult<()> {
+        Ok(())
+    }
+
+    fn copy_to_host(&self, _buffer: &GpuBuffer, _data: &mut [u8]) -> CfdResult<()> {
+        Ok(())
+    }
+
+    fn synchronize(&self) -> CfdResult<()> {
+        Ok(())
+    }
+
+    fn max_threads_per_block(&self) -> usize {
+        1
+    }
+
+    fn device_memory(&self) -> usize {
+        // Return approximate available system memory
+        8 * 1024 * 1024 * 1024 // 8 GB default
+    }
+}
+
+/// Auto-detect and create the best available GPU backend
+pub fn auto_detect_backend() -> Arc<dyn GpuBackend> {
+    // Try CUDA first (on any platform)
+    #[cfg(feature = "cuda")]
+    {
+        // TODO: Implement CUDA backend detection
+        tracing::info!("CUDA feature enabled but backend not yet implemented");
+    }
+
+    // Try Metal on macOS
+    #[cfg(all(target_os = "macos", feature = "metal"))]
+    {
+        use rtx_metal::MetalDevice;
+        if MetalDevice::is_available() {
+            tracing::info!("Metal backend available");
+            // TODO: Create and return Metal backend
+        }
+    }
+
+    // Fallback to CPU
+    tracing::info!("Using CPU fallback backend");
+    Arc::new(CpuBackend::new())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_launch_config_1d() {
+        let config = LaunchConfig::new_1d(1024, 256);
+        assert_eq!(config.grid, (4, 1, 1));
+        assert_eq!(config.block, (256, 1, 1));
+    }
+
+    #[test]
+    fn test_launch_config_2d() {
+        let config = LaunchConfig::new_2d(64, 64, 16, 16);
+        assert_eq!(config.grid, (4, 4, 1));
+        assert_eq!(config.block, (16, 16, 1));
+    }
+
+    #[test]
+    fn test_cpu_backend() {
+        let backend = CpuBackend::new();
+        assert_eq!(backend.backend_type(), BackendType::Cpu);
+        assert!(backend.is_available());
+    }
+
+    #[test]
+    fn test_auto_detect() {
+        let backend = auto_detect_backend();
+        assert!(backend.is_available());
+    }
+}