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CIODevice: Try to preallocate the exact needed buffer size in read_all().

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If we can get the exact file size from fstat(), it's a very good idea to use
it since it means we avoid eleventy thousand reallocations.
This commit is contained in:
Andreas Kling 2019-07-27 14:24:19 +02:00
parent a79d8d8ae5
commit 9ed7f4576b
Notes: sideshowbarker 2024-07-19 13:01:51 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/9ed7f4576be
1 changed files with 14 additions and 5 deletions
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19
Libraries/LibCore/CIODevice.cpp
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@ -4,6 +4,7 @@
#include <errno.h>
#include <stdio.h>
#include <sys/select.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <unistd.h>
@ -100,9 +101,17 @@ bool CIODevice::can_read() const
ByteBuffer CIODevice::read_all()
{
ByteBuffer buffer;
off_t file_size = 0;
struct stat st;
int rc = fstat(fd(), &st);
if (rc == 0)
file_size = st.st_size;
Vector<u8> data;
data.ensure_capacity(file_size);
if (!m_buffered_data.is_empty()) {
buffer = ByteBuffer::copy(m_buffered_data.data(), m_buffered_data.size());
data.append(m_buffered_data.data(), m_buffered_data.size());
m_buffered_data.clear();
}
@ -111,15 +120,15 @@ ByteBuffer CIODevice::read_all()
int nread = ::read(m_fd, read_buffer, sizeof(read_buffer));
if (nread < 0) {
set_error(nread);
return buffer;
return ByteBuffer::copy(data.data(), data.size());
}
if (nread == 0) {
set_eof(true);
break;
}
buffer.append(read_buffer, nread);
data.append((const u8*)read_buffer, nread);
}
return buffer;
return ByteBuffer::copy(data.data(), data.size());
}
ByteBuffer CIODevice::read_line(int max_size)