There are three develop flags that allow G1 to dump all objects on the heap to a text format:

G1PrintReachableAtInitialMark
G1VerifyDuringGCPrintReachable
G1PrintReachableBaseFile

Turning on this dumping code will dump all objects in all regions to the file specified by G1PrintReachableBaseFile,

Several things are disturbing with this code:
- The way the code opens a separate file and writes to it is pretty uncommon for our logging code
- The flags are develop flags, so not usable in product code - even druring verification
- The format the heap is dumped in is not a standard format so there is no tool support for it
- There is already standard ways of dumping the heap, using hprof for example.
- It is pretty unclear when the information logged by PrintReachable is useful.