Package Kit: Refactor BRepositoryCache to have GetPackageInfos(callback)...

... instead of GetIterator(). This allows us to avoid loading the
cache entirely in SetTo(), and allows consumers to read the cache
much more efficiently than loading it all into memory and then
freeing it again afterwards.

This technically breaks API/ABI, however the Package Kit APIs
are not considered stable (I don't think.)

All consumers adjusted. As we build the host tools with modern GCC
only, I made update_package_requires use a C++11 lambda function.
All others use out-of-line static methods.

"time pkgman list-repos -v" (which has to read the whole cache)
is ~0.5s before this change, and ~0.25s after this change,
on my test VM.

Change-Id: I6976b4cf5eb846fc925ed199dc00eb227fc81344
Reviewed-on: https://review.haiku-os.org/c/haiku/+/10247
Tested-by: Commit checker robot <[email protected]>
Reviewed-by: waddlesplash <[email protected]>
Reviewed-by: Andrew Lindesay <[email protected]>

headers/os/package/RepositoryCache.h

@@ -18,7 +18,7 @@ namespace BPackageKit {
 
 class BRepositoryCache {
 public:
-			typedef BPackageInfoSet::Iterator Iterator;
+			typedef bool (*GetPackageInfosCallback)(void* /* context */, const BPackageInfo& info);
 
 public:
 								BRepositoryCache();
@@ -30,20 +30,19 @@ public:
 			const BEntry&		Entry() const;
 			bool				IsUserSpecific() const;
 
-			void				SetIsUserSpecific(bool isUserSpecific);
-
-			uint32				CountPackages() const;
-			Iterator			GetIterator() const;
+			status_t			GetPackageInfos(GetPackageInfosCallback callback, void* context) const;
 
 private:
 			struct RepositoryContentHandler;
 
+			status_t			_ReadCache(const BPath& repositoryCachePath,
+									BRepositoryInfo& repositoryInfo,
+									GetPackageInfosCallback callback, void* context) const;
+
 private:
 			BEntry				fEntry;
 			BRepositoryInfo		fInfo;
 			bool				fIsUserSpecific;
-
-			BPackageInfoSet		fPackages;
 };