change sm->new_block() to return an optional

space_map.h

@@ -5,6 +5,7 @@
 #include "block_counter.h"
 
 #include <boost/shared_ptr.hpp>
+#include <boost/optional.hpp>
 
 //----------------------------------------------------------------
 
@@ -25,7 +26,14 @@ namespace persistent_data {
 
 		virtual void inc(block_address b) = 0;
 		virtual void dec(block_address b) = 0;
-		virtual block_address new_block() = 0;
+
+		// FIXME: change these to return an optional, failure is
+		// not that rare if we're restricting the area that's
+		// searched.
+		typedef boost::optional<block_address> maybe_block;
+
+		virtual maybe_block new_block() = 0;
+		virtual maybe_block new_block(block_address begin, block_address end) = 0;
 
 		virtual bool count_possibly_greater_than_one(block_address b) const = 0;
 

space_map_core.h

@@ -52,15 +52,19 @@ namespace persistent_data {
 				nr_free_++;
 		}
 
-		block_address new_block() {
+		maybe_block new_block() {
-			for (block_address i = 0; i < counts_.size(); i++)
+			return new_block(0, counts_.size());
+		}
+
+		maybe_block new_block(block_address begin, block_address end) {
+			for (block_address i = begin; i < min(end, counts_.size()); i++)
 				if (counts_[i] == 0) {
 					counts_[i] = 1;
 					nr_free_--;
 					return i;
 				}
 
-			throw std::runtime_error("no space");
+			return maybe_block();
 		}
 
 		bool count_possibly_greater_than_one(block_address b) const {

space_map_disk.cc

@@ -290,16 +290,22 @@ namespace {
 			set_count(b, old - 1);
 		}
 
-		block_address new_block() {
+		maybe_block new_block() {
-			// FIXME: silly to always start searching from the
+			// FIXME: keep track of the lowest free block so we
-			// beginning.
+			// can start searching from a suitable place.
-			block_address nr_indexes = div_up<block_address>(nr_blocks_, ENTRIES_PER_BLOCK);
+			return new_block(0, nr_blocks_);
-			for (block_address index = 0; index < nr_indexes; index++) {
+		}
+
+		maybe_block new_block(block_address begin, block_address end) {
+			block_address begin_index = begin / ENTRIES_PER_BLOCK;
+			block_address end_index = div_up<block_address>(end, ENTRIES_PER_BLOCK);
+
+			for (block_address index = begin_index; index < end_index; index++) {
 				index_entry ie = indexes_->find_ie(index);
 
 				bitmap bm(tm_, ie);
-				optional<unsigned> maybe_b = bm.find_free(0, (index == nr_indexes - 1) ?
+				optional<unsigned> maybe_b = bm.find_free((index == begin_index) ? (begin % ENTRIES_PER_BLOCK) : 0,
-							  nr_blocks_ % ENTRIES_PER_BLOCK : ENTRIES_PER_BLOCK);
+									  (index == end_index - 1) ? (end % ENTRIES_PER_BLOCK) : ENTRIES_PER_BLOCK);
 				if (maybe_b) {
 					block_address b = *maybe_b;
 					indexes_->save_ie(index, bm.get_ie());
@@ -310,7 +316,7 @@ namespace {
 				}
 			}
 
-			throw runtime_error("out of space");
+			return maybe_block();
 		}
 
 		bool count_possibly_greater_than_one(block_address b) const {

space_map_recursive.cc

@@ -85,14 +85,21 @@ namespace {
 			}
 		}
 
-		virtual block_address new_block() {
+		// new_block must not recurse.
-			// new_block can recurse, because we know it's
+		virtual boost::optional<block_address>
-			// looking up entries in the _previous_
+		new_block() {
-			// transaction.
+			cant_recurse("new_block");
 			recursing_lock lock(*this);
 			return sm_->new_block();
 		}
 
+		virtual boost::optional<block_address>
+		new_block(block_address begin, block_address end) {
+			cant_recurse("new_block(range)");
+			recursing_lock lock(*this);
+			return sm_->new_block(begin, end);
+		}
+
 		virtual bool count_possibly_greater_than_one(block_address b) const {
 			if (depth_)
 				return true;

thin_pool.cc

@@ -167,7 +167,11 @@ thin_pool::get_held_root() const
 block_address
 thin_pool::alloc_data_block()
 {
-	return md_->data_sm_->new_block();
+	optional<block_address> mb = md_->data_sm_->new_block();
+	if (!mb)
+		throw runtime_error("couldn't allocate new block");
+
+	return *mb;
 }
 
 void

transaction_manager.cc

@@ -30,10 +30,13 @@ transaction_manager::begin(block_address superblock, validator v)
 transaction_manager::write_ref
 transaction_manager::new_block(validator v)
 {
-	block_address b = sm_->new_block();
+	optional<block_address> mb = sm_->new_block();
-	sm_decrementer decrementer(sm_, b);
+	if (!mb)
-	write_ref wr = bm_->write_lock_zero(b, v);
+		throw runtime_error("couldn't allocate new block");
-	add_shadow(b);
+
+	sm_decrementer decrementer(sm_, *mb);
+	write_ref wr = bm_->write_lock_zero(*mb, v);
+	add_shadow(*mb);
 	decrementer.dont_bother();
 	return wr;
 }
@@ -46,7 +49,12 @@ transaction_manager::shadow(block_address orig, validator v)
 		return make_pair(bm_->write_lock(orig, v), false);
 
 	read_ref src = bm_->read_lock(orig, v);
-	write_ref dest = bm_->write_lock_zero(sm_->new_block(), v);
+
+	optional<block_address> mb = sm_->new_block();
+	if (!mb)
+		throw runtime_error("couldn't allocate new block");
+
+	write_ref dest = bm_->write_lock_zero(*mb, v);
 	::memcpy(dest.data(), src.data(), MD_BLOCK_SIZE);
 
 	ref_t count = sm_->get_count(orig);