Memory cache reserves 12MB free RAM to prevent watchdog from killing …

…the app before memory warning is sent

SDWebImage/SDImageCache.m

@@ -10,10 +10,37 @@
 #import "SDWebImageDecoder.h"
 #import <CommonCrypto/CommonDigest.h>
 #import "SDWebImageDecoder.h"
+#import <mach/mach.h>
+#import <mach/mach_host.h>
+
+static SDImageCache *instance;
 
 static NSInteger cacheMaxCacheAge = 60*60*24*7; // 1 week
+static natural_t minFreeMemLeft = 1024*1024*12; // reserve 12MB RAM
 
-static SDImageCache *instance;
+// inspired by http://stackoverflow.com/questions/5012886/knowing-available-ram-on-an-ios-device
+static natural_t get_free_memory(void)
+{
+    mach_port_t host_port;
+    mach_msg_type_number_t host_size;
+    vm_size_t pagesize;
+
+    host_port = mach_host_self();
+    host_size = sizeof(vm_statistics_data_t) / sizeof(integer_t);
+    host_page_size(host_port, &pagesize);
+
+    vm_statistics_data_t vm_stat;
+
+    if (host_statistics(host_port, HOST_VM_INFO, (host_info_t)&vm_stat, &host_size) != KERN_SUCCESS)
+    {
+        NSLog(@"Failed to fetch vm statistics");
+        return 0;
+    }
+
+    /* Stats in bytes */
+    natural_t mem_free = vm_stat.free_count * pagesize;
+    return mem_free;
+}
 
 @implementation SDImageCache
 
@@ -151,6 +178,10 @@ - (void)notifyDelegate:(NSDictionary *)arguments
 
     if (image)
     {
+        if (get_free_memory() < minFreeMemLeft)
+        {
+            [memCache removeAllObjects];
+        }    
         [memCache setObject:image forKey:key];
 
         if ([delegate respondsToSelector:@selector(imageCache:didFindImage:forKey:userInfo:)])
@@ -196,7 +227,11 @@ - (void)storeImage:(UIImage *)image imageData:(NSData *)data forKey:(NSString *)
     {
         return;
     }
-
+
+    if (get_free_memory() < minFreeMemLeft)
+    {
+        [memCache removeAllObjects];
+    }
     [memCache setObject:image forKey:key];
 
     if (toDisk)
@@ -248,6 +283,10 @@ - (UIImage *)imageFromKey:(NSString *)key fromDisk:(BOOL)fromDisk
         image = SDScaledImageForPath(key, [NSData dataWithContentsOfFile:[self cachePathForKey:key]]);
         if (image)
         {
+            if (get_free_memory() < minFreeMemLeft)
+            {
+                [memCache removeAllObjects];
+            }
             [memCache setObject:image forKey:key];
         }
     }