private void allocate_root_block()
{
/* Default each root block to store 1024 root definitions
* Each definition is a start and end pointer, thus size of block
* is sizeof(root_header) + 2 * 1024 * sizeof(byte *)
*/
chunk_header *chk = allocate_chunk(sizeof(root_header) + 2048 * sizeof(byte *));
if (chk == null)
{
Formatter.WriteLine("gengc: add_root_block: allocate_chunk() returned null",
Program.arch.DebugOutput);
libsupcs.OtherOperations.Halt();
}
chk->flags &= ~(1 << 4); // not large block
chk->flags |= 1 << 5; // is root block
root_header *r = (root_header *)((byte *)chk + sizeof(chunk_header));
r->next = hdr->roots;
r->capacity = 1024;
r->size = 0;
hdr->roots = r;
}
public void AddRoots(byte *start, byte *end)
{
if (hdr->roots == null || hdr->roots->size == hdr->roots->capacity)
{
allocate_root_block();
}
root_header *r = hdr->roots;
byte ** rptr = (byte **)((byte *)r + sizeof(root_header) +
r->size * sizeof(byte *) * 2);
*rptr++ = start;
*rptr++ = end;
r->size++;
Formatter.Write("gengc: adding root: ", Program.arch.DebugOutput);
Formatter.Write((ulong)start, "X", Program.arch.DebugOutput);
Formatter.Write(" - ", Program.arch.DebugOutput);
Formatter.Write((ulong)end, "X", Program.arch.DebugOutput);
Formatter.WriteLine(Program.arch.DebugOutput);
}
public void DoCollection()
{
/* We only want one collection to run at once. If we just used a lock{} section,
* then all threads that request a collection whilst one is already running would
* have to wait for the current collection to finish, then run one themselves
* immediately afterwards. This is wasteful as they can just rely on the already
* running collection to be good enough.
*
* Thus, we protect the entry to the function so only one thread can check if a
* collection is running and immediately start one if it isn't. This is a short
* code block so other threads won't have to wait long, they will then see the
* collection_in_progress flag is true and exit.
*
* The flag is reset at function exit atomically so no need for to reacquire the
* mutex.
*/
bool can_continue = false;
while (can_continue == false)
{
libsupcs.Monitor.Enter(collection_mutex);
{
if (collection_in_progress)
{
Formatter.WriteLine("gengc: attempt to run collection whilst already in progress",
Program.arch.DebugOutput);
libsupcs.Monitor.Exit(collection_mutex);
libsupcs.OtherOperations.AsmBreakpoint();
return;
}
if (alloc_in_progress == false)
{
collection_in_progress = true;
can_continue = true;
}
}
libsupcs.Monitor.Exit(collection_mutex);
}
/* Run a collection. Process is:
*
* 1) Whiten all objects (all chunks/small objects that are not root blocks)
* (this is done implicitly on assignment and on freeing)
* 2) Grey those listed in a root block
* 3a) Set blackened_count to 0
* 3b) Iterate though all blocks. If a grey is encountered:
* 3b.1) Iterate through the object on native int boundaries
* 3b.2) Grey all white objects it points to
* 3b.3) Blacken the object
* 3b.4) blackened_count++
* 3c) If blackened_count > 0 loop to 3a
* 4) Iterate through again, reclaiming white blocks to be free, and
* whitening black blocks (there should be no grey blocks now)
*/
#if GENGC_BASICDEBUG
Formatter.WriteLine("gengc: Starting collection", Program.arch.DebugOutput);
#endif
/* grey root blocks */
#if GENGC_BASICDEBUG
Formatter.WriteLine("gengc: greying roots... ", Program.arch.DebugOutput);
#endif
root_header *cur_root_hdr = hdr->roots;
while (cur_root_hdr != null)
{
for (int i = 0; i < cur_root_hdr->size; i++)
{
byte *root_start = *(byte **)((byte *)cur_root_hdr + sizeof(root_header) +
i * 2 * sizeof(byte *));
byte *root_end = *(byte **)((byte *)cur_root_hdr + sizeof(root_header) +
(i * 2 + 1) * sizeof(byte *));
grey_object(root_start, root_end);
#if GENGC_DEBUG
Formatter.Write((ulong)root_start, "X", Program.arch.DebugOutput);
Formatter.Write(" - ", Program.arch.DebugOutput);
Formatter.Write((ulong)root_end, "X", Program.arch.DebugOutput);
Formatter.WriteLine(Program.arch.DebugOutput);
#endif
}
cur_root_hdr = cur_root_hdr->next;
}
#if GENGC_BASICDEBUG
Formatter.WriteLine("done", Program.arch.DebugOutput);
#endif
/* blacken reachable blocks */
#if GENGC_BASICDEBUG
Formatter.Write("gengc: blackening reachable blocks... ", Program.arch.DebugOutput);
#endif
int blackened_count;
int total_blackened = 0;
int small_blackened = 0;
int large_blackened = 0;
int loops = 0;
int block_count = 0; // debugging count to ensure we traverse the whole tree
chunk_header *chk;
do
{
blackened_count = 0;
block_count = 0;
/* Iterate all blocks */
// Get the first block
chk = hdr->root_used_chunk;
while (chk->left != hdr->nil)
{
chk = chk->left;
}
while (chk != hdr->nil)
{
block_count++;
if ((chk->flags & 0x30) == 0x10)
{
/* large object - is it grey? */
if ((chk->flags & 0x3) == 0x3)
{
byte *obj_start = (byte *)chk + sizeof(chunk_header);
byte *obj_end = obj_start + (int)chk->length;
/* grey all it points to */
grey_object(obj_start, obj_end);
/* blacken the object */
chk->flags &= ~0x1;
blackened_count++;
large_blackened++;
#if GENGC_DEBUG
Formatter.Write("gengc: INFO: greying large object: ", Program.arch.DebugOutput);
Formatter.Write((ulong)obj_start, "X", Program.arch.DebugOutput);
Formatter.Write(" - ", Program.arch.DebugOutput);
Formatter.Write((ulong)obj_end, "X", Program.arch.DebugOutput);
Formatter.WriteLine(Program.arch.DebugOutput);
#endif
}
}
else if ((chk->flags & 0x30) == 0x0)
{
/* small object array, iterate through each */
sma_header *smhdr = (sma_header *)((byte *)chk + sizeof(chunk_header));
for (int i = 0; i < smhdr->total_count; i += 8)
{
uint *uint_ptr = (uint *)((byte *)smhdr + sizeof(sma_header) +
i / 2);
for (int bit_idx = 0; bit_idx < 8; bit_idx++)
{
uint flag_pattern = 0x3U << (bit_idx * 4);
uint grey_pattern = 0x3U << (bit_idx * 4);
uint black_pattern = 0x2U << (bit_idx * 4);
if ((*uint_ptr & flag_pattern) == grey_pattern)
{
byte *data_start = (byte *)smhdr + sizeof(sma_header) +
smhdr->total_count * 4;
byte *obj_start = data_start + (i + bit_idx) *
smhdr->obj_length;
byte *obj_end = obj_start + smhdr->obj_length;
/* grey all it points to */
grey_object(obj_start, obj_end);
/* blacken the object */
*uint_ptr &= ~flag_pattern;
*uint_ptr |= black_pattern;
blackened_count++;
small_blackened++;
}
}
}
}
// Loop to the next chunk
chk = TreeSuccessor(hdr, 1, chk);
}
total_blackened += blackened_count;
loops++;
#if GENGC_DEBUG
Formatter.Write("gengc: loop visited ", Program.arch.DebugOutput);
Formatter.Write((ulong)block_count, Program.arch.DebugOutput);
Formatter.WriteLine(" blocks", Program.arch.DebugOutput);
#endif
} while (blackened_count > 0);
#if GENGC_BASICDEBUG
Formatter.WriteLine("done", Program.arch.DebugOutput);
#endif
/* Iterate through again, setting white to free and black to white */
#if GENGC_BASICDEBUG
Formatter.Write("gengc: freeing white blocks... ", Program.arch.DebugOutput);
#endif
// Get the first block
chk = hdr->root_used_chunk;
while (chk->left != hdr->nil)
{
chk = chk->left;
}
int white_large_objects = 0;
int white_small_objects = 0;
int black_large_objects = 0;
int black_small_objects = 0;
block_count = 0;
while (chk != hdr->nil)
{
block_count++;
if ((chk->flags & 0x30) == 0x10)
{
/* large object - is it white? */
if ((chk->flags & 0x3) == 0x3)
{
// TODO: delete large object
// Can we do a tree node delete whilst traversal is in progress?
white_large_objects++;
}
else if ((chk->flags & 0x3) == 0x2)
{
// its black - set back to white
chk->flags &= ~0x3;
chk->flags |= 0x1;
black_large_objects++;
}
}
else if ((chk->flags & 0x30) == 0x0)
{
/* small object array, iterate through each */
sma_header *smhdr = (sma_header *)((byte *)chk + sizeof(chunk_header));
for (int i = 0; i < smhdr->total_count; i += 8)
{
uint *uint_ptr = (uint *)((byte *)smhdr + sizeof(sma_header) +
i / 2);
for (int bit_idx = 0; bit_idx < 8; bit_idx++)
{
uint flag_pattern = 0x3U << (bit_idx * 4);
uint white_pattern = 0x1U << (bit_idx * 4);
uint black_pattern = 0x2U << (bit_idx * 4);
/* debugging - check we are not freeing a process/thread etc */
byte *data_start = (byte *)smhdr + sizeof(sma_header) +
smhdr->total_count * 4;
byte *obj_start = data_start + (i + bit_idx) *
smhdr->obj_length;
if ((*uint_ptr & flag_pattern) == white_pattern)
{
/* free the object */
*uint_ptr &= ~flag_pattern;
smhdr->free_count++;
(*smhdr->global_free_count)++;
white_small_objects++;
}
else if ((*uint_ptr & flag_pattern) == black_pattern)
{
/* whiten the object */
*uint_ptr &= ~flag_pattern;
*uint_ptr |= white_pattern;
black_small_objects++;
}
else if ((*uint_ptr & flag_pattern) == flag_pattern)
{
Formatter.Write("gengc: WARNING: object at ", Program.arch.DebugOutput);
Formatter.Write((ulong)obj_start, "X", Program.arch.DebugOutput);
Formatter.Write(" is grey on final loop: ", Program.arch.DebugOutput);
Formatter.Write(*uint_ptr & flag_pattern, "X", Program.arch.DebugOutput);
Formatter.WriteLine(Program.arch.DebugOutput);
}
}
}
}
// Loop to the next chunk
chk = TreeSuccessor(hdr, 1, chk);
}
#if GENGC_BASICDEBUG
Formatter.WriteLine("done", Program.arch.DebugOutput);
#endif
#if GENGC_DEBUG
Formatter.Write("gengc: final loop visited ", Program.arch.DebugOutput);
Formatter.Write((ulong)block_count, Program.arch.DebugOutput);
Formatter.WriteLine(" blocks", Program.arch.DebugOutput);
/* Sanity check to ensure we visited all nodes */
Formatter.Write("gengc: total number of blocks: ", Program.arch.DebugOutput);
Formatter.Write((ulong)hdr->used_chunks, Program.arch.DebugOutput);
Formatter.WriteLine(Program.arch.DebugOutput);
#endif
#if GENGC_BASICDEBUG
Formatter.Write("gengc: Collection completed: ", Program.arch.DebugOutput);
Formatter.Write((ulong)white_large_objects, Program.arch.DebugOutput);
Formatter.Write(" large objects and ", Program.arch.DebugOutput);
Formatter.Write((ulong)white_small_objects, Program.arch.DebugOutput);
Formatter.WriteLine(" small objects freed", Program.arch.DebugOutput);
#endif
#if GENGC_DEBUG
Formatter.Write("gengc: ", Program.arch.DebugOutput);
Formatter.Write((ulong)black_large_objects, Program.arch.DebugOutput);
Formatter.Write(" large objects and ", Program.arch.DebugOutput);
Formatter.Write((ulong)black_small_objects, Program.arch.DebugOutput);
Formatter.WriteLine(" small objects not freed", Program.arch.DebugOutput);
Formatter.Write("gengc: ", Program.arch.DebugOutput);
Formatter.Write((ulong)large_blackened, Program.arch.DebugOutput);
Formatter.Write(" large objects and ", Program.arch.DebugOutput);
Formatter.Write((ulong)small_blackened, Program.arch.DebugOutput);
Formatter.WriteLine(" small objects were blackened", Program.arch.DebugOutput);
#endif
#if GENGC_BASICDEBUG
Formatter.Write("gengc: ", Program.arch.DebugOutput);
Formatter.Write((ulong)total_blackened, Program.arch.DebugOutput);
Formatter.WriteLine(" objects remain in use", Program.arch.DebugOutput);
Formatter.Write("gengc: ", Program.arch.DebugOutput);
Formatter.Write((ulong)loops, Program.arch.DebugOutput);
Formatter.WriteLine(" loops required to blacken all in-use objects", Program.arch.DebugOutput);
#endif
allocs = 0;
collection_in_progress = false;
}
