Add PerfTools::DumpHeap

src/core_ext/gc.cr

@@ -0,0 +1,5 @@
+{% if flag?(:gc_none) || flag?(:wasm32) %}
+  require "./gc/none"
+{% else %}
+  require "./gc/boehm"
+{% end %}

src/core_ext/gc/boehm.cr

@@ -0,0 +1,37 @@
+lib LibGC
+  GC_I_PTRFREE = 0
+  GC_I_NORMAL  = 1
+
+  fun get_kind_and_size = GC_get_kind_and_size(p : Void*, psize : SizeT*) : Int
+
+  alias ReachableObjectFunc = Void*, SizeT, Void* -> Void
+
+  fun enumerate_reachable_objects_inner = GC_enumerate_reachable_objects_inner(proc : ReachableObjectFunc, client_data : Void*)
+
+  fun register_disclaim_proc = GC_register_disclaim_proc(kind : Int, proc : Void* -> Int, mark_from_all : Int)
+end
+
+module GC
+  # Returns whether *ptr* is a pointer to the base of an atomic allocation.
+  def self.atomic?(ptr : Pointer) : Bool
+    LibGC.get_kind_and_size(ptr, nil) == LibGC::GC_I_PTRFREE
+  end
+
+  # Walks the entire GC heap, yielding each allocation's base address and size
+  # to the given *block*.
+  #
+  # The *block* must not allocate memory using the GC.
+  def self.each_reachable_object(&block : Void*, UInt64 ->) : Nil
+    Thread.stop_world
+    GC.lock_write
+    begin
+      LibGC.enumerate_reachable_objects_inner(LibGC::ReachableObjectFunc.new do |obj, bytes, client_data|
+        fn = client_data.as(typeof(pointerof(block))).value
+        fn.call(obj, bytes.to_u64!)
+      end, pointerof(block))
+    ensure
+      GC.unlock_write
+      Thread.start_world
+    end
+  end
+end

src/core_ext/gc/none.cr

@@ -0,0 +1,13 @@
+module GC
+  # Returns whether *ptr* is a pointer to the base of an atomic allocation.
+  def self.atomic?(ptr : Pointer) : Bool
+    false
+  end
+
+  # Walks the entire GC heap, yielding each allocation's base address and size
+  # to the given *block*.
+  #
+  # The *block* must not allocate memory using the GC.
+  def self.each_reachable_object(&block : Void*, UInt64 ->) : Nil
+  end
+end

src/perf_tools/dump_heap.cr

@@ -0,0 +1,90 @@
+require "./common"
+require "../core_ext/gc"
+
+# Functions to produce binary dumps of the running process's GC heap, useful for
+# out-of-memory analysis.
+#
+# Methods in this module are independent from other tools like `MemProf`.
+module PerfTools::DumpHeap
+  # Dumps a compact representation of the GC heap to the given *io*, sufficient
+  # to reconstruct all pointers between allocations.
+  #
+  # All writes to *io* must not allocate memory using the GC. For `IO::Buffered`
+  # this can be achieved by disabling write buffering (`io.sync = true`).
+  #
+  # The binary dump consists of a sequential list of allocation records. Each
+  # record contains the following fields, all 64-bit little-endian integers,
+  # unless otherwise noted:
+  #
+  # * The base address of the allocation.
+  # * The byte size of the allocation. This may be larger than the size
+  #   originally passed to `GC.malloc` or a similar method, as the GC may
+  #   reserve trailing padding bytes for alignment. Additionally, for an atomic
+  #   allocation, the most significant bit of this field is set as well.
+  # * The pointer-sized word at the start of the allocation. If this allocation
+  #   corresponds to an instance of a Crystal reference type, the lower bytes
+  #   will contain that type's ID.
+  # * If the allocation is non-atomic, then for each inner pointer, the field
+  #   offset relative to the allocation base and the pointer value are written;
+  #   this list is terminated by a single `UInt64::MAX` field. Atomic records do
+  #   not have this list.
+  #
+  # All the records are then terminated by a single `UInt64::MAX` field.
+  def self.graph(io : IO) : Nil
+    GC.collect
+
+    GC.each_reachable_object do |obj, bytes|
+      is_atomic = GC.atomic?(obj)
+      io.write_bytes(obj.address.to_u64!)
+      io.write_bytes(bytes.to_u64! | (is_atomic ? Int64::MIN : 0_i64))
+
+      ptr = obj.as(Void**)
+      io.write_bytes(ptr.value.address.to_u64!)
+
+      unless is_atomic
+        b = ptr
+        e = (obj + bytes).as(Void**)
+        while ptr < e
+          inner = ptr.value
+          if GC.is_heap_ptr(inner)
+            io.write_bytes((ptr.address &- b.address).to_u64!)
+            io.write_bytes(inner.address.to_u64!)
+          end
+          ptr += 1
+        end
+        io.write_bytes(UInt64::MAX)
+      end
+    end
+
+    io.write_bytes(UInt64::MAX)
+  end
+
+  # Dumps the contents of the GC heap to the given *io*.
+  #
+  # All writes to *io* must not allocate memory using the GC. For `IO::Buffered`
+  # this can be achieved by disabling write buffering (`io.sync = true`).
+  #
+  # The binary dump consists of a sequential list of allocation records. Each
+  # record contains the following fields, all 64-bit little-endian integers,
+  # unless otherwise noted:
+  #
+  # * The base address of the allocation.
+  # * The byte size of the allocation. This may be larger than the size
+  #   originally passed to `GC.malloc` or a similar method, as the GC may
+  #   reserve trailing padding bytes for alignment. Additionally, for an atomic
+  #   allocation, the most significant bit of this field is set as well.
+  # * The full contents of the allocation.
+  #
+  # All the records are then terminated by a single `UInt64::MAX` field.
+  def self.full(io : IO) : Nil
+    GC.collect
+
+    GC.each_reachable_object do |obj, bytes|
+      io.write_bytes(obj.address.to_u64!)
+      io.write_bytes(bytes.to_u64! | (GC.atomic?(obj) ? Int64::MIN : 0_i64))
+      io.write(obj.as(UInt8*).to_slice(bytes)) # TODO: 32-bit overflow?
+    end
+
+    io.write_bytes(UInt64::MAX)
+  end
+end

src/perf_tools/mem_prof.cr

@@ -1,4 +1,5 @@
 require "./common"
+require "../core_ext/gc"
 
 # A simple in-memory memory profiler that tracks all allocations and
 # deallocations by the garbage-collecting allocator.
@@ -650,13 +651,6 @@ module PerfTools::MemProf
   init
 end
 
-lib LibGC
-  GC_I_PTRFREE = 0
-  GC_I_NORMAL  = 1
-
-  fun register_disclaim_proc = GC_register_disclaim_proc(kind : Int, proc : Void* -> Int, mark_from_all : Int)
-end
-
 module GC
   # :nodoc:
   def self.malloc(size : LibC::SizeT) : Void*