Fast, persistent, atomically incrementing, cross-process counters. Download


Approx 385 million increments per second. Measured with:


Linux, Intel, GCC.

How It Works

Fastcounters uses a memory mapped file and increments the counters with the atomic xaddl instruction; the code is taken from the linux kernel.


GPL, since it uses code from the linux kernel.

Creating the counter file

Create a file with four anonymous counters like this:
fastcounters -n4 counters.dat
(They will be named C0 thru C3)
Or create a file with three named counters like this:
fastcounters -n cats,dogs,snakes counters.dat

Incrementing Counters

In a C program, you can increment a counter like this:
int res;
if(fcntrs_incr(&fc, 0, &res)) {
    // handle error

Ways of Addressing Counters

There are three ways of addressing counters:

Literal Int

Shown in the example above.

Defined Constant

Given a counters file, you can generate a C fragment with:
fastcounters -poh counters.dat
This will produce output like:
#define COUNTER_cats      0
#define COUNTER_dogs      1
#define COUNTER_snakes    2
You can use these defined constants to access the counters.

Dynamic Name Lookup

You can dynamically resolve counter names to IDs:
int cnt_id;
if(fcntrs_resolve_name(fc, "dogs", &cnt_id)) {
    // handle error
Since this lookup is signficantly slower than incrementing a counter, the result should be cached. One way to do this is with static variables:
static int cnt_id = -1;
if(cnt_id == -1) { // first time
    if(fcntrs_resolve_name(fc, "dogs", &cnt_id)) {