Modify arena custom interface for detachment.

include/bitcoin/system/arena.hpp

@@ -51,9 +51,19 @@ class arena
         return do_is_equal(other);
     }
 
-    /// Non-linear allocator is a nop and returns nullptr.
-    /// Reset linear allocator and return starting address (not pmr interface).
-    virtual void* initialize() NOEXCEPT = 0;
+    /// Non-linear allocator just returns next address.
+    /// Linear allocator resets to and returns buffer first address.
+    /// Detachable linear allocator allocates buffer returns its first address.
+    virtual void* start() NOEXCEPT = 0;
+
+    /// Non-linear allocator just returns zero.
+    /// Linear allocator returns current allocation size.
+    /// Detachable linear allocator detaches allocation and returns its size.
+    virtual size_t detach() NOEXCEPT = 0;
+
+    /// Non-linear and linear allocator is a nop.
+    /// Detachable linear allocator frees the memory associated with ptr.
+    virtual void release(void* ptr, size_t bytes) NOEXCEPT = 0;
 
 private:
     virtual void* do_allocate(size_t bytes, size_t align) THROWS = 0;
@@ -83,7 +93,9 @@ class BC_API default_arena final
 {
 public:
     static arena* get() NOEXCEPT;
-    void* initialize() NOEXCEPT override;
+    void* start() NOEXCEPT override;
+    size_t detach() NOEXCEPT override;
+    void release(void* ptr, size_t bytes) NOEXCEPT override;
 
 private:
     void* do_allocate(size_t bytes, size_t align) THROWS override;

src/arena.cpp

@@ -57,11 +57,20 @@ bool default_arena::do_is_equal(const arena& other) const NOEXCEPT
     return &other == this;
 }
 
-void* default_arena::initialize() NOEXCEPT
+void* default_arena::start() NOEXCEPT
 {
     return nullptr;
 }
 
+size_t default_arena::detach() NOEXCEPT
+{
+    return zero;
+}
+
+void default_arena::release(void*, size_t) NOEXCEPT
+{
+}
+
 BC_POP_WARNING()
 
 } // namespace libbitcoin

test/test.hpp

@@ -127,11 +127,20 @@ class reporting_arena
     size_t dec_count{};
     size_t dec_bytes{};
 
-    void* initialize() NOEXCEPT override
+    void* start() NOEXCEPT override
     {
         return nullptr;
     }
 
+    size_t detach() NOEXCEPT override
+    {
+        return zero;
+    }
+
+    void release(void*, size_t) NOEXCEPT override
+    {
+    }
+
 private:
     void* do_allocate(size_t bytes, size_t align) override
     {
@@ -189,11 +198,20 @@ class mock_arena
     size_t do_deallocate_align{};
     mutable const arena* do_is_equal_address{};
 
-    void* initialize() NOEXCEPT override
+    void* start() NOEXCEPT override
     {
         return nullptr;
     }
 
+    size_t detach() NOEXCEPT override
+    {
+        return zero;
+    }
+
+    void release(void*, size_t) NOEXCEPT override
+    {
+    }
+
 private:
     void* do_allocate(size_t bytes, size_t align) THROWS override
     {