Add option to use or not use fadvise in decompressors

This way we can make this configurable from outside.

Author: joto

include/osmium/io/bzip2_compression.hpp

@@ -276,7 +276,7 @@ namespace osmium {
 
             std::string read() override {
                 const auto offset = ftell(m_file.file());
-                if (offset > 0) {
+                if (offset > 0 && want_buffered_pages_removed()) {
                     osmium::io::detail::remove_buffered_pages(fileno(m_file.file()), static_cast<std::size_t>(offset));
                 }
 #ifdef _MSC_VER
@@ -325,7 +325,9 @@ namespace osmium {
 
             void close() override {
                 if (m_bzfile) {
-                    osmium::io::detail::remove_buffered_pages(fileno(m_file.file()));
+                    if (want_buffered_pages_removed()) {
+                        osmium::io::detail::remove_buffered_pages(fileno(m_file.file()));
+                    }
 #ifdef _MSC_VER
                     osmium::detail::disable_invalid_parameter_handler diph;
 #endif

include/osmium/io/compression.hpp

@@ -93,6 +93,8 @@ namespace osmium {
             std::atomic<std::size_t> m_file_size{0};
             std::atomic<std::size_t> m_offset{0};
 
+            std::atomic_bool m_want_buffered_pages_removed{true};
+
         public:
 
             enum {
@@ -133,6 +135,14 @@ namespace osmium {
                 m_offset = offset;
             }
 
+            bool want_buffered_pages_removed() const noexcept {
+                return m_want_buffered_pages_removed;
+            }
+
+            void set_want_buffered_pages_removed(bool value) noexcept {
+                m_want_buffered_pages_removed = value;
+            }
+
         }; // class Decompressor
 
         /**
@@ -352,7 +362,9 @@ namespace osmium {
                     }
                 } else {
                     buffer.resize(osmium::io::Decompressor::input_buffer_size);
-                    osmium::io::detail::remove_buffered_pages(m_fd, m_offset);
+                    if (want_buffered_pages_removed()) {
+                        osmium::io::detail::remove_buffered_pages(m_fd, m_offset);
+                    }
                     const auto nread = detail::reliable_read(m_fd, &*buffer.begin(), osmium::io::Decompressor::input_buffer_size);
                     buffer.resize(std::string::size_type(nread));
                 }
@@ -365,7 +377,9 @@ namespace osmium {
 
             void close() override {
                 if (m_fd >= 0) {
-                    osmium::io::detail::remove_buffered_pages(m_fd);
+                    if (want_buffered_pages_removed()) {
+                        osmium::io::detail::remove_buffered_pages(m_fd);
+                    }
                     const int fd = m_fd;
                     m_fd = -1;
                     osmium::io::detail::reliable_close(fd);

include/osmium/io/gzip_compression.hpp

@@ -223,7 +223,7 @@ namespace osmium {
 #else
 # if ZLIB_VERNUM >= 0x1240
                 const auto offset = ::gzoffset(m_gzfile);
-                if (offset > 0) {
+                if (offset > 0 && want_buffered_pages_removed()) {
                     osmium::io::detail::remove_buffered_pages(m_fd, static_cast<std::size_t>(offset));
                 }
 # endif
@@ -243,7 +243,9 @@ namespace osmium {
 
             void close() override {
                 if (m_gzfile) {
-                    osmium::io::detail::remove_buffered_pages(m_fd);
+                    if (want_buffered_pages_removed()) {
+                        osmium::io::detail::remove_buffered_pages(m_fd);
+                    }
 #ifdef _MSC_VER
                     osmium::detail::disable_invalid_parameter_handler diph;
 #endif