scc::util::FileDesc Class Reference

File descriptor. More...

#include <filedesc.h>

Public Member Functions
	FileDesc (int fd)
	Wrap an open file descriptor.
	FileDesc (const FileDesc &other)
	Copy construct by duplication.
FileDesc &	operator= (const FileDesc &other)
	Copy assign by duplication.
	FileDesc (FileDesc &&other)
	Move construct.
FileDesc &	operator= (FileDesc &&other)
	Move assign.
	operator int () const
	Cast const file descriptor to int.
int	fd () const
	Return the file descriptor.
void	close ()
	Signal safe close.
void	dup (int)
	Duplicate a file descriptor. More...

Detailed Description

File descriptor.

Assumes ownership of an open file descriptor.

Wraps a file descriptor object and allows safe duplication and destruction. Safe for signal interruption.

Copy operations duplicate the file descriptor.

Example of using FileDesc to protect a file descriptor opened with the clib open api, from scclib/util/unittest/fs.cc

TEST(FsExampleTest, sparse_and_trunc)
{
    system_error err;
    fs::remove_all("sandbox", &err);
    fs::create_dir("sandbox");
    auto curdir = fs::get_current_dir();
    cout << "curdir: " << curdir << endl;
 
    fs::change_dir("sandbox");
 
    string s("this is a test of the emergency sizing system\n");
    cout << "sparse test with string len=" << s.size() << endl;
 
    string fn("sparse_file");
 
    auto write_sparse = [&fn, &s](off_t loc)
    {
        // use clib to write data into the middle of the file
        // if we use fstream, the system may truncate the file
 
        // use system wrapper FileDesc to ensure the file is always closed
        scc::util::FileDesc fd(scc::util::safe_open_throw(fn.c_str(), O_WRONLY));
        
        lseek(fd, loc, SEEK_SET);
        safe_write_throw(fd, &s[0], s.size());
        
        cout << "wrote " << s.size() << " bytes at loc " << loc << endl;
    };
 
    fs::create_reg(fn);
    fs::set_size(fn, 16384);            // 16 K file, with a 0 at the end
    
    auto st = fs::file_stat(fn);
    cout << "12288 hole at start of file:\n" << st << endl;
 
    ASSERT_EQ(st.size, 16384);
    ASSERT_EQ(st.alloc_size, 4096);     // the last block has data
 
    auto sm = fs::sparse_map(fn);
    cout << setw(6) << "start" << setw(6) << "data" << endl;
    for (auto& x : sm)
    {
        cout << setw(6) << x.first << setw(6) << x.second << endl;
    }
    
    std::map<int64_t,int64_t> ver;
    
    ver[0] = 12287;                     // 12288 sized hole at 0 (beginning)
    ASSERT_EQ(sm, ver);
 
    write_sparse(1024);                 // write the string at 1024, causing first block to be written
    
    st = fs::file_stat(fn);
    cout << "8192 hole in middle of file\n" << st << endl;
 
    ASSERT_EQ(st.alloc_size, 8192);
 
    sm = fs::sparse_map(fn);
    cout << setw(6) << "start" << setw(6) << "data" << endl;
    for (auto& x : sm)
    {
        cout << setw(6) << x.first << setw(6) << x.second << endl;
    }
 
    ver.clear();
    ver[4096] = 12287;                  // 8192 sized hole at 4096 (middle)
    ASSERT_EQ(sm, ver);
 
    fs::set_size(fn, 12288);
 
    st = fs::file_stat(fn);
    cout << "8192 hole at end of file\n" << st << endl;
 
    ASSERT_EQ(st.alloc_size, 4096);
 
    sm = fs::sparse_map(fn);
    cout << setw(6) << "start" << setw(6) << "data" << endl;
    for (auto& x : sm)
    {
        cout << setw(6) << x.first << setw(6) << x.second << endl;
    }
 
    ver.clear();
    ver[4096] = 12287;                  // 8192 sized hole at 4096 (end)
    ASSERT_EQ(sm, ver);
 
    ifstream f(fn);
    f.seekg(1024);
    string val;
    val.resize(s.size(), '\x01');
    f.read(&val[0], val.size());
    ASSERT_EQ(val, s);
 
    fs::change_dir(curdir);
    fs::remove_all("sandbox");
}

Examples

util/unittest/filedesc.cc, and util/unittest/fs.cc.

Definition at line 65 of file filedesc.h.

Member Function Documentation

dup()

void FileDesc::dup

(

int

fd

)

Duplicate a file descriptor.

This descriptor is now a duplicate of the input descriptor.

If the input file descriptor is invalid, this descriptor will also be invalid.

Definition at line 50 of file filedesc.cc.

---

The documentation for this class was generated from the following files:

• util/pub/util/filedesc.h
• util/filedesc.cc