From 25a4d50e7ec93ce9821e535578752485db90601d Mon Sep 17 00:00:00 2001
From: Nathaniel Walizer <robots.are.love@gmail.com>
Date: Sat, 11 Jan 2025 21:27:49 -0800
Subject: [PATCH] Add support for simultaneous mapped files in Windows

---
 src/win/filemap.c | 56 ++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 51 insertions(+), 5 deletions(-)

diff --git a/src/win/filemap.c b/src/win/filemap.c
index 2965155..a5a0959 100644
--- a/src/win/filemap.c
+++ b/src/win/filemap.c
@@ -9,21 +9,67 @@
 #include "filemap.h"
 
 
-// TODO: Support multiple filemaps
-static HANDLE hMap;
+// Support multiple filemaps
+
+typedef struct map_handle_t {
+    const void* mem;
+    HANDLE hMap;
+    struct map_handle_t* next;
+} map_handle;
+
+static map_handle* map_handle_head = NULL;
+
+static HANDLE take_map_handle(const void* mem) {
+    HANDLE handle = NULL;
+    map_handle* last = NULL;
+    for (   map_handle* node = map_handle_head;
+            NULL != node;
+            last = node, node = node->next) {
+        if (mem == node->mem) {
+            if (NULL == last) {
+                map_handle_head = node->next;
+            } else {
+                last->next = node->next;
+            }
+            handle = node->hMap;
+            free(node);
+        }
+    }
+    return handle;
+}
+
+static void store_map_handle(const void* mem, HANDLE handle) {
+    map_handle* node = malloc(sizeof(map_handle));
+    node->mem = mem;
+    node->hMap = handle;
+    node->next = map_handle_head;
+    map_handle_head = node;
+}
 
 
 void* map_file(FILE* file, int size) {
+    void* mem = NULL;
+
     HANDLE hFile = (HANDLE)_get_osfhandle(fileno(file));
 
-    hMap = CreateFileMappingA(
+    HANDLE hMap = CreateFileMappingA(
             hFile, 0, PAGE_READONLY, 0, size, 0
         );
 
-    return MapViewOfFile(hMap, FILE_MAP_READ, 0, 0, size);
+    if (NULL != hMap) {
+        mem = MapViewOfFile(hMap, FILE_MAP_READ, 0, 0, size);
+        if (NULL == mem) {
+            CloseHandle(hMap);
+        } else {
+            store_map_handle(mem, hMap);
+        }
+    }
+
+    return mem;
 }
 
 void unmap_file(void* mem, int size) {
     UnmapViewOfFile(mem);
-    CloseHandle(hMap);
+    HANDLE handle = take_map_handle(mem);
+    if (NULL != handle) CloseHandle(handle);
 }