A comment on ref-counting

C Smart Pointers

What this is

This project is an attempt to bring smart pointer constructs to the (GNU) C programming language.

Features

unique_ptr, shared_ptr macros, and smart type attribute
Destructor support for cleanup
Custom variable metadata on allocation
Cross-platform: tested under linux 3.18.6-1, Mac OS X Yosemite 10.10, and Windows 7 (with MinGW and the Cygwin port of GCC)

Installing

With a package manager

Mac OS X: brew install snaipe/soft/libcsptr
AUR: yaourt -S libcsptr

Ubuntu:

$ sudo add-apt-repository ppa:snaipewastaken/ppa
$ sudo apt-get update
$ sudo apt-get install libcsptr-dev

Building from source

Prerequisites

To compile the library, GCC 4.6+ is needed.

Installation

Clone this repository
run mkdir build && cd $_ && cmake -DCMAKE_INSTALL_PREFIX=$HOME .. && make && make install
from the project root for a local install, or run
mkdir build && cd $_ && cmake -DCMAKE_INSTALL_PREFIX=/usr .. && make && sudo make install for a global install.

Examples

Simple unique_ptr: simple1.c:

#include <stdio.h>
#include <csptr/smart_ptr.h>

int main(void) {
    // some_int is an unique_ptr to an int with a value of 1.
    smart int *some_int = unique_ptr(int, 1);

    printf("%p = %d\n", some_int, *some_int);

    // some_int is destroyed here
    return 0;
}

Shell session:

$ gcc -std=c99 -o simple1 simple1.c -lcsptr
$ valgrind ./simple1
==3407== Memcheck, a memory error detector
==3407== Copyright (C) 2002-2013, and GNU GPL\'d, by Julian Seward et al.
==3407== Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info
==3407== Command: ./test1
==3407==
0x53db068 = 1
==3407==
==3407== HEAP SUMMARY:
==3407==     in use at exit: 0 bytes in 0 blocks
==3407==   total heap usage: 1 allocs, 1 frees, 48 bytes allocated
==3407==
==3407== All heap blocks were freed -- no leaks are possible
==3407==
==3407== For counts of detected and suppressed errors, rerun with: -v
==3407== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

Simple unique_ptr with destructor:

#include <unistd.h>
#include <fcntl.h>
#include <csptr/smart_ptr.h>

struct log_file {
    int fd;
    // ...
};

void cleanup_log_file(void *ptr, void *meta) {
    (void) meta;
    close(((struct log_file *) ptr)->fd);
}

int main(void) {
    smart struct log_file *log = unique_ptr(struct log_file, {
            .fd = open("/dev/null", O_WRONLY | O_APPEND),
            // ...
        }, cleanup_log_file);

    write(log->fd, "Hello", 5);

    // cleanup_log_file is called, then log is freed
    return 0;
}

Allocating a smart array and printing its contents before destruction:

#include <stdio.h>
#include <csptr/smart_ptr.h>
#include <csptr/array.h>

void print_int(void *ptr, void *meta) {
    (void) meta;
    // ptr points to the current element
    // meta points to the array metadata (global to the array), if any.
    printf("%d\n", *(int*) ptr);
}

int main(void) {
    // Destructors for array types are run on every element of the
    // array before destruction.
    smart int *ints = unique_ptr(int[5], {5, 4, 3, 2, 1}, print_int);
    // ints == {5, 4, 3, 2, 1}

    // Smart arrays are length-aware
    for (size_t i = 0; i < array_length(ints); ++i) {
        ints[i] = i + 1;
    }
    // ints == {1, 2, 3, 4, 5}

    return 0;
}

More examples

Using a different memory allocator (although most will replace malloc/free):

#include <csptr/smart_ptr.h>

void *some_allocator(size_t);
void some_deallocator(void *);

int main(void) {
    smalloc_allocator = (s_allocator) {some_allocator, some_deallocator};
    // ...
    return 0;
}

Automatic cleanup on error cases:

#include <unistd.h>
#include <fcntl.h>
#include <csptr/smart_ptr.h>

struct log_file {
    int fd;
    // ...
};

static void close_log(void *ptr, void *meta) {
    (void) meta;
    struct log_file *log = ptr;
    if (log->fd != -1)
        close(log->fd);
}

struct log_file *open_log(const char *path) {
    smart struct log_file *log = shared_ptr(struct log_file, {0}, close_log);
    if (!log) // failure to allocate
        return NULL; // nothing happens, destructor is not called

    log->fd = open(path, O_WRONLY | O_APPEND | O_CREAT, 0644);
    if (log->fd == -1) // failure to open
        return NULL; // log gets destroyed, file descriptor is not closed since fd == -1.

    return sref(log); // a new reference on log is returned, it does not get destoyed
}

int main(void) {
    smart struct log_file *log = open_log("/dev/null");
    // ...
    return 0; // file descriptor is closed, log is freed
}

Using named parameters:

#include <csptr/smart_ptr.h>

void nothing(void *ptr, void *meta) {}

int main(void) {
    struct { int a; } m = { 1 };

    smart int *i = unique_ptr(int,
            .dtor = nothing,
            .value = 42,
            .meta = { &m, sizeof (m) }
        );

    return 0;
}

FAQ

Q. Why didn't you use C++ you moron ?
A. Because when I first started this, I was working on a C project. Also, because it's fun.

Q. Can I use this on a serious project ?
A. Yes, but as this project has not been widely used, there might be some bugs. Beware!

Q. How did you make this ?
A. Here's a link to my blog post on the matter.

	static CSPTR_INLINE size_t atomic_add(volatile size_t *count, const size_t limit, const size_t val) {
	size_t old_count, new_count;
	do {
	old_count = *count;
	if (old_count == limit)
	abort();
	new_count = old_count + val;
	} while (!__sync_bool_compare_and_swap(count, old_count, new_count));
	return new_count;
	}

snaipe / libcsptr Goto Github PK

libcsptr's Introduction

C Smart Pointers

What this is

Features

Installing

With a package manager

Building from source

Prerequisites

Installation

Examples

More examples

FAQ

libcsptr's People

Contributors

Stargazers

Watchers

Forkers

libcsptr's Issues

include "common.h"

Q. Why didn't you use C++ you moron?

A. Because C makes smaller and faster executables. There is no ABI which is not made for C. Using C, I can focus on the job done. Using C++, one first has to satisfy the language[1], and just then one can try and get the job done.

defer is coming into ISO C (gasp!) Good read for us C "morons", who use clang or gnuc __cleanup__

[1] What do I mean by "satisfy the language"? motivation section of this paper explains it clearly

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`defer` is coming into ISO C (gasp!) Good read for us C "morons", who use clang or gnuc `cleanup`