Cache file descriptors when reading frames, for better readahead and fewer syscalls.

[nageru] / frame_on_disk.h

diff --git a/frame_on_disk.h b/frame_on_disk.h
index a0f46ad171ab6bf0e4d91a846a99727fae0c6691..184385792528130df7e3ba16637385c0c14a35db 100644 (file)
--- a/frame_on_disk.h
+++ b/frame_on_disk.h
@@ -19,6 +19,19 @@ struct FrameOnDisk {
 extern std::vector<FrameOnDisk> frames[MAX_STREAMS];  // Under frame_mu.
 extern std::vector<std::string> frame_filenames;  // Under frame_mu.
 
-std::string read_frame(FrameOnDisk frame);
+// A helper class to read frames from disk. It caches the file descriptor
+// so that the kernel has a better chance of doing readahead when it sees
+// the sequential reads. (For this reason, each display has a private
+// FrameReader. Thus, we can easily keep multiple open file descriptors around
+// for a single .frames file.)
+class FrameReader {
+public:
+       ~FrameReader();
+       std::string read_frame(FrameOnDisk frame);
+
+private:
+       int fd = -1;
+       int last_filename_idx = -1;
+};
 
 #endif  // !defined(_FRAME_ON_DISK_H)