Windows available memory support.

Author: ltfish

src/sysmem.rs

@@ -1,9 +1,15 @@
 //! System memory queries.
 
-/// Available system memory in bytes, from `/proc/meminfo` (Linux). Returns
-/// `None` on other platforms or on parse failure (callers then skip any
-/// memory-based heuristics).
+/// Available system memory in bytes, when determinable. Returns `None` on
+/// unsupported platforms or on failure (callers then skip memory-based
+/// heuristics and show "n/a").
 pub fn available_bytes() -> Option<u64> {
+    platform_available()
+}
+
+/// Linux: `MemAvailable` from `/proc/meminfo`.
+#[cfg(target_os = "linux")]
+fn platform_available() -> Option<u64> {
     let meminfo = std::fs::read_to_string("/proc/meminfo").ok()?;
     for line in meminfo.lines() {
         if let Some(rest) = line.strip_prefix("MemAvailable:") {
@@ -14,6 +20,39 @@ pub fn available_bytes() -> Option<u64> {
     None
 }
 
+/// Windows: available physical memory via `GlobalMemoryStatusEx`.
+#[cfg(windows)]
+fn platform_available() -> Option<u64> {
+    #[repr(C)]
+    struct MemoryStatusEx {
+        length: u32,
+        memory_load: u32,
+        total_phys: u64,
+        avail_phys: u64,
+        total_page_file: u64,
+        avail_page_file: u64,
+        total_virtual: u64,
+        avail_virtual: u64,
+        avail_extended_virtual: u64,
+    }
+    #[link(name = "kernel32")]
+    extern "system" {
+        fn GlobalMemoryStatusEx(buffer: *mut MemoryStatusEx) -> i32;
+    }
+    let mut status: MemoryStatusEx = unsafe { std::mem::zeroed() };
+    status.length = std::mem::size_of::<MemoryStatusEx>() as u32;
+    if unsafe { GlobalMemoryStatusEx(&mut status) } != 0 {
+        Some(status.avail_phys)
+    } else {
+        None
+    }
+}
+
+#[cfg(not(any(target_os = "linux", windows)))]
+fn platform_available() -> Option<u64> {
+    None
+}
+
 /// Format a byte count as `GiB`/`MiB`.
 pub fn human_bytes(bytes: u64) -> String {
     let gib = bytes as f64 / (1024.0 * 1024.0 * 1024.0);