Store offset in Reader directly from Decompressor

Author: joto

include/osmium/io/compression.hpp

@@ -90,7 +90,7 @@ namespace osmium {
 
         class Decompressor {
 
-            std::atomic<std::size_t> m_offset{0};
+            std::atomic<std::size_t>* m_offset_ptr{nullptr};
 
             std::atomic_bool m_want_buffered_pages_removed{false};
 
@@ -118,12 +118,14 @@ namespace osmium {
                 return true;
             }
 
-            std::size_t offset() const noexcept {
-                return m_offset;
+            void set_offset_ptr(std::atomic<std::size_t>* offset_ptr) noexcept {
+                m_offset_ptr = offset_ptr;
             }
 
             void set_offset(const std::size_t offset) noexcept {
-                m_offset = offset;
+                if (m_offset_ptr) {
+                    *m_offset_ptr = offset;
+                }
             }
 
             bool want_buffered_pages_removed() const noexcept {

include/osmium/io/reader.hpp

@@ -257,7 +257,7 @@ namespace osmium {
                 return fd;
             }
 
-            static std::unique_ptr<Decompressor> make_decompressor(const osmium::io::File& file, int fd) {
+            std::unique_ptr<Decompressor> make_decompressor(const osmium::io::File& file, int fd) {
                 const auto& factory = osmium::io::CompressionFactory::instance();
                 if (file.buffer()) {
                     return factory.create_decompressor(file.compression(), file.buffer(), file.buffer_size());
@@ -332,6 +332,8 @@ namespace osmium {
                     m_pool = &thread::Pool::default_instance();
                 }
 
+                m_decompressor->set_offset_ptr(&m_offset);
+
                 std::promise<osmium::io::Header> header_promise;
                 m_header_future = header_promise.get_future();
 
@@ -521,9 +523,6 @@ namespace osmium {
              * do an expensive system call.
              */
             std::size_t offset() const noexcept {
-                if (m_decompressor->is_real()) {
-                    return m_decompressor->offset();
-                }
                 return m_offset;
             }