Add some UBC eviction code after talking to Amit (and it doesn't even require...

base/test_file_util_mac.cc

Index: base/test_file_util_mac.cc
===================================================================
--- base/test_file_util_mac.cc	(revision 12089)
+++ base/test_file_util_mac.cc	(working copy)
@@ -4,14 +4,36 @@
 
 #include "base/test_file_util.h"
 
+#include <sys/mman.h>

[Mark Mentovai, 2009/03/19 14:50:07]

Come on, what alphabet are we using today?

+#include <errno.h>
 #include "base/logging.h"
+#include "base/file_util.h"
 
 namespace file_util {
 
 bool EvictFileFromSystemCache(const FilePath& file) {
-  // There is no way that we can think of to dump something from the UBC.  You
-  // can add something so when you open it, it doesn't go in, but that won't
-  // work here.
+  // There aren't any really direct ways to purge a file from the UBC.  From
+  // talking w/ Amit Singh, the safest is to mmap the file, do a msync to

[Mark Mentovai, 2009/03/19 14:50:07]

I would do "an" msync unless you have a novel way to pronounce msync that
doesn't start with "em."

Also, this could be revised to be a little clearer, like by putting "then"
before "do."

+  // invalidate the memory.  The next open should then have to load the
+  // file from disk.
+
+  // We use MemoryMappedFile because it mmaps MAP_FILE | MAP_SHARED (it doesn't

[Mark Mentovai, 2009/03/19 14:50:07]

That's kind of obvious from reading MemoryMappedFile::MapFileToMemory.  This
comment isn't contributing anything really except implying that MAP_FILE |
MAP_SHARED is needed to make this scheme work.  Is it?  If so, it ought to be
explicit.

+  // list MAP_FILE, but that's the default and it doesn't use MAP_ANON to avoid
+  // that default).
+
+  file_util::MemoryMappedFile mmap;

[Mark Mentovai, 2009/03/19 14:50:07]

I would not name a variable mmap, mmap is the name of a system call and this is
confusing.

+  if (!mmap.Initialize(file)) {
+    DLOG(WARNING) << "failed to memory map " << file.value();
+    return false;
+  }
+  
+  if (msync(const_cast<uint8*>(mmap.data()), mmap.length(),
+            MS_INVALIDATE) != 0) {
+    DLOG(WARNING) << "failed to invalidate memory map of " << file.value() 
+        << ", errno: " << errno;
+    return false;
+  }
+  
   return true;
 }