Add low memory alarm system

CMakeLists.txt

@@ -95,6 +95,7 @@ if(PLATFORM STREQUAL "web-meta")
     set(SOURCES
         src/data_win.c
         src/binary_reader.c
+        src/low_memory.c
     )
 else()
     file(GLOB SOURCES src/*.c)

src/low_memory.c

@@ -0,0 +1,32 @@
+#include "utils.h"
+
+#define MAX_CALLBACKS 64
+
+typedef bool(*LowMemoryAlarmCallback)(void);
+
+LowMemoryAlarmCallback lowMemoryAlarmCallbacks[MAX_CALLBACKS];
+int lowMemoryAlarmCallbackCount = 0;
+
+// Call when memory is running low.  This triggers low memory alarm callback
+// functions which evict caches from memory to free it up.
+bool lowMemoryAlarm()
+{
+    bool didSomething = false;
+    for (int i = 0; i < lowMemoryAlarmCallbackCount; i++) {
+        bool result = lowMemoryAlarmCallbacks[i]();
+        if (result)
+            didSomething = true;
+    }
+    return didSomething;
+}
+
+// Registers a low memory alarm callback.  When a low memory alarm is triggered,
+// the function provided will be called, and it should free memory if possible.
+void registerLowMemoryAlarmCallback(bool(*callbackFunction)(void))
+{
+    if (lowMemoryAlarmCallbackCount >= MAX_CALLBACKS) {
+        fprintf(stderr, "registerLowMemoryAlarmCallback: Cannot register another callback, %d already registered.\n", lowMemoryAlarmCallbackCount);
+        return;
+    }
+    lowMemoryAlarmCallbacks[lowMemoryAlarmCallbackCount++] = callbackFunction;
+}

src/utils.h

@@ -32,6 +32,14 @@
     #define TYPEOF(x) long long
 #endif
 
+#if defined(__GNUC__) && (__GNUC__ >= 3 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 96))
+#define LIKELY(cond)   __builtin_expect(!!(cond), 1)
+#define UNLIKELY(cond) __builtin_expect(!!(cond), 0)
+#else
+#define LIKELY(cond) (cond)
+#define UNLIKELY(cond) (cond)
+#endif
+
 #define forEach(type, item, array, count) \
     for (TYPEOF(count) item##_i_ = 0; item##_i_ < (count); ++item##_i_) \
     for (type* item = &(array)[item##_i_]; item; item = NULL)
@@ -80,46 +88,71 @@ static inline void* requireNotNullFunction(void* ptr, const char* file, int line
 #define requireNotNull(ptr) requireNotNullFunction((void*)ptr, __FILE__, __LINE__, #ptr)
 #define requireNotNullMessage(ptr, msg) requireNotNullFunction((void*)ptr, __FILE__, __LINE__, msg)
 
+// Call when memory is running low.  This triggers low memory alarm callback
+// functions which evict caches from memory to free it up.
+bool lowMemoryAlarm();
+
+// Registers a low memory alarm callback.  When a low memory alarm is triggered,
+// the function provided will be called.  Your callback should return TRUE if it
+// freed memory, or FALSE if nothing changed.
+void registerLowMemoryAlarmCallback(bool(*callbackFunction)(void));
+
 // Safe allocation macros - check for nullptr and abort with file/line info
 static inline void *safeMallocFunction(size_t size, const char *file, int line) {
-    void *ret = malloc(size);
-    if (!ret) {
-        fprintf(stderr, "FATAL: malloc(%zu) failed at %s:%d\n", size, file, line);
-        abort();
+    while (true) {
+        void* ret = malloc(size);
+        if (LIKELY(ret)) {
+            return ret;
+        }
+        if (!lowMemoryAlarm()) {
+            fprintf(stderr, "FATAL: malloc(%zu) failed at %s:%d\n", size, file, line);
+            abort();
+        }
     }
-    return ret;
 }
 #define safeMalloc(size) safeMallocFunction(size, __FILE__, __LINE__)
 
 static inline void *safeCallocFunction(size_t count, size_t size, const char *file, int line) {
-    void *ret = calloc(count, size);
-    if (!ret) {
-        fprintf(stderr, "FATAL: calloc(%zu, %zu) failed at %s:%d\n", count, size, file, line);
-        abort();
+    while (true) {
+        void *ret = calloc(count, size);
+        if (LIKELY(ret)) {
+            return ret;
+        }
+        if (!lowMemoryAlarm()) {
+            fprintf(stderr, "FATAL: calloc(%zu, %zu) failed at %s:%d\n", count, size, file, line);
+            abort();
+        }
     }
-    return ret;
 }
 #define safeCalloc(count, size) safeCallocFunction(count, size, __FILE__, __LINE__)
 
 static inline void *safeReallocFunction(void *ptr, size_t size, const char *file, int line) {
-    void *ret = realloc(ptr, size);
-    if (!ret) {
-        fprintf(stderr, "FATAL: realloc(%zu) failed at %s:%d\n", size, file, line);
-        abort();
+    while (true) {
+        void *ret = realloc(ptr, size);
+        if (LIKELY(ret)) {
+            return ret;
+        }
+        if (!lowMemoryAlarm()) {
+            fprintf(stderr, "FATAL: realloc(%zu) failed at %s:%d\n", size, file, line);
+            abort();
+        }
     }
-    return ret;
 }
 #define safeRealloc(ptr, size) safeReallocFunction(ptr, size, __FILE__, __LINE__)
 
 #ifdef PLATFORM_PS2
 
 static inline void *safeMemalignFunction(size_t alignment, size_t size, const char *file, int line) {
-    void *ret = memalign(alignment, size);
-    if (!ret) {
-        fprintf(stderr, "FATAL: memalign(%zu, %zu) failed at %s:%d\n", alignment, size, file, line);
-        abort();
+    while (true) {
+        void *ret = memalign(alignment, size);
+        if (LIKELY(ret)) {
+            return ret;
+        }
+        if (!lowMemoryAlarm()) {
+            fprintf(stderr, "FATAL: memalign(%zu, %zu) failed at %s:%d\n", alignment, size, file, line);
+            abort();
+        }
     }
-    return ret;
 }
 #define safeMemalign(alignment, size) safeMemalignFunction(alignment, size, __FILE__, __LINE__)