133 lines
4.6 KiB
C++
133 lines
4.6 KiB
C++
//: Reclaiming memory when it's no longer used.
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:(scenario new_reclaim)
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def main [
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10:&:num <- new number:type
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20:num <- deaddress 10:&:num
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abandon 10:&:num
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30:&:num <- new number:type # must be same size as abandoned memory to reuse
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40:num <- deaddress 30:&:num
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50:bool <- equal 20:num, 40:num
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]
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# both allocations should have returned the same address
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+mem: storing 1 in location 50
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//: When abandoning addresses we'll save them to a 'free list', segregated by size.
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//: Before, suppose variable V contains address A which points to payload P:
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//: location V contains an alloc-id N
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//: location V+1 contains A
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//: location A contains alloc-id N
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//: location A+1 onwards contains P
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//: Additionally, suppose the head of the free list is initially F.
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//: After abandoning:
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//: location V contains invalid alloc-id -1
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//: location V+1 contains 0
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//: location A contains invalid alloc-id N
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//: location A+1 contains the previous head of free-list F
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:(before "End routine Fields")
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map<int, int> free_list;
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:(before "End Primitive Recipe Declarations")
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ABANDON,
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:(before "End Primitive Recipe Numbers")
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put(Recipe_ordinal, "abandon", ABANDON);
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:(before "End Primitive Recipe Checks")
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case ABANDON: {
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if (!inst.products.empty()) {
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raise << maybe(get(Recipe, r).name) << "'abandon' shouldn't write to any products in '" << to_original_string(inst) << "'\n" << end();
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break;
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}
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for (int i = 0; i < SIZE(inst.ingredients); ++i) {
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if (!is_mu_address(inst.ingredients.at(i)))
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raise << maybe(get(Recipe, r).name) << "ingredients of 'abandon' should be addresses, but ingredient " << i << " is '" << to_string(inst.ingredients.at(i)) << '\n' << end();
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break;
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}
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break;
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}
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:(before "End Primitive Recipe Implementations")
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case ABANDON: {
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for (int i = 0; i < SIZE(current_instruction().ingredients); ++i) {
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reagent/*copy*/ ingredient = current_instruction().ingredients.at(i);
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canonize(ingredient);
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abandon(get_or_insert(Memory, ingredient.value+/*skip alloc id*/1), payload_size(ingredient));
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//? cerr << "clear after abandon: " << ingredient.value << '\n';
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put(Memory, /*alloc id*/ingredient.value, /*invalid*/-1);
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put(Memory, /*address*/ingredient.value+1, 0);
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}
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break;
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}
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:(code)
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void abandon(int address, int payload_size) {
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put(Memory, address, /*invalid alloc-id*/-1);
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//? cerr << "abandon: " << address << '\n';
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// clear rest of payload
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for (int curr = address+1; curr < address+payload_size; ++curr)
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put(Memory, curr, 0);
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// append existing free list to address
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trace("abandon") << "saving " << address << " in free-list of size " << payload_size << end();
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put(Memory, address+/*skip invalid alloc-id*/1, get_or_insert(Current_routine->free_list, payload_size));
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put(Current_routine->free_list, payload_size, address);
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}
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int payload_size(reagent/*copy*/ x) {
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x.properties.push_back(pair<string, string_tree*>("lookup", NULL));
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lookup_memory_core(x, /*check_for_null*/false);
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return size_of(x)+/*alloc id*/1;
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}
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:(after "Allocate Special-cases")
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if (get_or_insert(Current_routine->free_list, size)) {
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trace("abandon") << "picking up space from free-list of size " << size << end();
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int result = get_or_insert(Current_routine->free_list, size);
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trace("mem") << "new alloc from free list: " << result << end();
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put(Current_routine->free_list, size, get_or_insert(Memory, result+/*skip alloc id*/1));
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// clear 'deleted' tag
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put(Memory, result, 0);
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// clear next pointer
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put(Memory, result+/*skip alloc id*/1, 0);
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for (int curr = result; curr < result+size; ++curr) {
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if (get_or_insert(Memory, curr) != 0) {
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raise << maybe(current_recipe_name()) << "memory in free list was not zeroed out: " << curr << '/' << result << "; somebody wrote to us after free!!!\n" << end();
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break; // always fatal
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}
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}
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return result;
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}
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:(scenario new_differing_size_no_reclaim)
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def main [
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1:&:num <- new number:type
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2:num <- deaddress 1:&:num
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abandon 1:&:num
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3:&:@:num <- new number:type, 2 # different size
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4:num <- deaddress 3:&:@:num
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5:bool <- equal 2:num, 4:num
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]
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# no reuse
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+mem: storing 0 in location 5
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:(scenario new_reclaim_array)
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def main [
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10:&:@:num <- new number:type, 2
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20:num <- deaddress 10:&:@:num
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abandon 10:&:@:num
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30:&:@:num <- new number:type, 2 # same size
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40:num <- deaddress 30:&:@:num
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50:bool <- equal 20:num, 40:num
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]
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# both calls to new returned identical addresses
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+mem: storing 1 in location 50
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:(scenario lookup_of_abandoned_address_raises_error)
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% Hide_errors = true;
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def main [
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1:&:num <- new num:type
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3:&:num <- copy 1:&:num
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abandon 1:&:num
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5:num/raw <- copy *3:&:num
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]
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+error: main: address is already abandoned in '5:num/raw <- copy *3:&:num'
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