public static unsafe IntPtr GetNewThunksBlock()
{
IntPtr nextThunksBlock;
// Check the most recently mapped thunks block. Each mapping consists of multiple
// thunk stubs pages, and multiple thunk data pages (typically 8 pages of each in a single mapping)
if (s_currentlyMappedThunkBlocksIndex < Constants.NumThunkBlocksPerMapping)
{
nextThunksBlock = s_currentlyMappedThunkBlocks[s_currentlyMappedThunkBlocksIndex++];
#if DEBUG
s_currentlyMappedThunkBlocks[s_currentlyMappedThunkBlocksIndex - 1] = IntPtr.Zero;
Debug.Assert(nextThunksBlock != IntPtr.Zero);
#endif
}
else
{
nextThunksBlock = InternalCalls.RhAllocateThunksMapping();
if (nextThunksBlock == IntPtr.Zero)
{
// We either ran out of memory and can't do anymore mappings of the thunks templates sections,
// or we are using the managed runtime services fallback, which doesn't provide the
// file mapping feature (ex: older version of mrt100.dll, or no mrt100.dll at all).
// The only option is for the caller to attempt and recycle unused thunks to be able to
// find some free entries.
return(IntPtr.Zero);
}
// Each mapping consists of multiple blocks of thunk stubs/data pairs. Keep track of those
// so that we do not create a new mapping until all blocks in the sections we just mapped are consumed
IntPtr currentThunksBlock = nextThunksBlock;
int thunkBlockSize = InternalCalls.RhpGetThunkBlockSize();
for (int i = 0; i < Constants.NumThunkBlocksPerMapping; i++)
{
s_currentlyMappedThunkBlocks[i] = currentThunksBlock;
currentThunksBlock += thunkBlockSize;
}
s_currentlyMappedThunkBlocksIndex = 1;
}
Debug.Assert(nextThunksBlock != IntPtr.Zero);
// Setup the thunks in the new block as a linked list of thunks.
// Use the first data field of the thunk to build the linked list.
IntPtr dataAddress = InternalCalls.RhpGetThunkDataBlockAddress(nextThunksBlock);
for (int i = 0; i < Constants.NumThunksPerBlock; i++)
{
if (i == (Constants.NumThunksPerBlock - 1))
{
*((IntPtr *)(dataAddress)) = IntPtr.Zero;
}
else
{
*((IntPtr *)(dataAddress)) = dataAddress + Constants.ThunkDataSize;
}
#if DEBUG
// Debug flag in the second data cell indicating the thunk is not used
*((IntPtr *)(dataAddress + IntPtr.Size)) = new IntPtr(-1);
#endif
dataAddress += Constants.ThunkDataSize;
}
return(nextThunksBlock);
}