Merge pull request #105 from etodanik/patch-1

This PR addresses performance issues of shared memory buffer (#104) by
optimizing memcpy() usage with chunks of data.

src/pshmbuffer.c

@@ -1,7 +1,8 @@
 /*
  * The MIT License
  *
- * Copyright (C) 2010-2023 Alexander Saprykin <saprykin.spb@gmail.com>
+ * Copyright (C) 2010-2024 Alexander Saprykin <saprykin.spb@gmail.com>
+ * Copyright (C) 2024 Danny Povolotski <dannypovolotski@gmail.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -158,7 +159,7 @@ p_shm_buffer_read (PShmBuffer *buf,
  psize write_pos;
  psize data_aval;
  psize to_copy;
- puint i;
+ psize start_pos;
  ppointer addr;
 
  if (P_UNLIKELY (buf == NULL || storage == NULL || len == 0)) {
@@ -193,10 +194,16 @@ p_shm_buffer_read (PShmBuffer *buf,
  data_aval = pp_shm_buffer_get_used_space (buf);
  to_copy = (data_aval <= len) ? data_aval : len;
 
- for (i = 0; i < to_copy; ++i)
- memcpy ((pchar *) storage + i,
- (pchar *) addr + P_SHM_BUFFER_DATA_OFFSET + ((read_pos + i) % buf->size),
- 1);
+ start_pos = read_pos % buf->size;
+
+ if (start_pos + to_copy <= buf->size) {
+ memcpy ((pchar *) storage, (pchar *) addr + P_SHM_BUFFER_DATA_OFFSET + start_pos, to_copy);
+ } else {
+ psize first_part_size = buf->size - start_pos;
+
+ memcpy ((pchar *) storage, (pchar *) addr + P_SHM_BUFFER_DATA_OFFSET + start_pos, first_part_size);
+ memcpy ((pchar *) storage + first_part_size, (pchar *) addr + P_SHM_BUFFER_DATA_OFFSET, to_copy - first_part_size);
+ }
 
  read_pos = (read_pos + to_copy) % buf->size;
  memcpy ((pchar *) addr + P_SHM_BUFFER_READ_OFFSET, &read_pos, sizeof (read_pos));
@@ -215,7 +222,7 @@ p_shm_buffer_write (PShmBuffer *buf,
 {
  psize read_pos;
  psize write_pos;
- puint i;
+ psize start_pos;
  ppointer addr;
 
  if (P_UNLIKELY (buf == NULL || data == NULL || len == 0)) {
@@ -247,10 +254,16 @@ p_shm_buffer_write (PShmBuffer *buf,
  return 0;
  }
 
- for (i = 0; i < len; ++i)
- memcpy ((pchar *) addr + P_SHM_BUFFER_DATA_OFFSET + ((write_pos + i) % buf->size),
- (pchar *) data + i,
- 1);
+ start_pos = write_pos % buf->size;
+
+ if (start_pos + len <= buf->size) {
+ memcpy ((pchar *) addr + P_SHM_BUFFER_DATA_OFFSET + start_pos, (pchar *) data, len);
+ } else {
+ psize first_part_size = buf->size - start_pos;
+
+ memcpy ((pchar *) addr + P_SHM_BUFFER_DATA_OFFSET + start_pos, (pchar *) data, first_part_size);
+ memcpy ((pchar *) addr + P_SHM_BUFFER_DATA_OFFSET, (pchar *) data + first_part_size, len - first_part_size);
+ }
 
  write_pos = (write_pos + len) % buf->size;
  memcpy ((pchar *) addr + P_SHM_BUFFER_WRITE_OFFSET, &write_pos, sizeof (write_pos));