class Raindrops

Each Raindrops object is a container that holds several counters. It is internally a page-aligned, shared memory area that allows atomic increments, decrements, assignments and reads without any locking.

rd = Raindrops.new 4
rd.incr(0, 1)   -> 1
rd.to_ary       -> [ 1, 0, 0, 0 ]

Unlike many classes in this package, the core Raindrops class is intended to be portable to all reasonably modern *nix systems supporting mmap(). Please let us know if you have portability issues, patches or pull requests at raindrops-public@yhbt.net

Constants

MAX

The maximum value a raindrop counter can hold

PAGE_SIZE

The size of one page of memory for a mmap()-ed Raindrops region. Typically 4096 bytes under Linux.

SIZE

The size (in bytes) of a slot in a Raindrops object. This is the size of a word on single CPU systems and the size of the L1 cache line size if detectable.

Defaults to 128 bytes if undetectable.

TCP

This is a frozen hash storing the numeric values maps platform-independent symbol keys to platform-dependent numeric values. These states are all valid values for the Raindrops::TCP_Info#state field.

The platform-independent names of the keys in this hash are:

- :ESTABLISHED
- :SYN_SENT
- :SYN_RECV
- :FIN_WAIT1
- :FIN_WAIT2
- :TIME_WAIT
- :CLOSE
- :CLOSE_WAIT
- :LAST_ACK
- :LISTEN
- :CLOSING

This is only supported on platforms where TCP_Info is supported, currently FreeBSD, OpenBSD, and Linux-based systems.

Public Class Methods

new(size, io: nil) → raindrops object click to toggle source

Initializes a Raindrops object to hold size counters. size is only a hint and the actual number of counters the object has is dependent on the CPU model, number of cores, and page size of the machine. The actual size of the object will always be equal or greater than the specified size. If io is provided, then the Raindrops memory will be backed by the specified file; otherwise, it will allocate anonymous memory. The IO object must respond to truncate, as this is used to set the size of the file. If zero is provided, then the memory region is zeroed prior to returning. This is only meaningful if io is also provided; in that case it controls whether any existing counter values in io are retained (false) or whether it is entirely zeroed (true).

# File lib/raindrops.rb, line 56
def initialize(size, io: nil, zero: false)
  # This ruby wrapper exists to handle the keyword-argument handling,
  # which is otherwise kind of awkward in C. We delegate the keyword
  # arguments to the _actual_ initialize implementation as positional
  # args.
  initialize_cimpl(size, io, zero)
end

Public Instance Methods

rd[index] → value click to toggle source

Returns the value of the slot designated by index

static VALUE aref(VALUE self, VALUE index)
{
        return  ULONG2NUM(*addr_of(self, index));
}
rd[index] = value click to toggle source

Assigns value to the slot designated by index

static VALUE aset(VALUE self, VALUE index, VALUE value)
{
        unsigned long *addr = addr_of(self, index);

        *addr = NUM2ULONG(value);

        return value;
}
capa → Integer click to toggle source

Returns the number of slots allocated (but not necessarily used) by the Raindrops object.

static VALUE capa(VALUE self)
{
        return SIZET2NUM(get(self)->capa);
}
decr(index[, number]) → result click to toggle source

Decrements the value referred to by the index by number. number defaults to 1 if unspecified.

static VALUE decr(int argc, VALUE *argv, VALUE self)
{
        unsigned long nr = incr_decr_arg(argc, argv);

        return ULONG2NUM(__sync_sub_and_fetch(addr_of(self, argv[0]), nr));
}
evaporate! → nil click to toggle source

Releases mmap()-ed memory allocated for the Raindrops object back to the OS. The Ruby garbage collector will also release memory automatically when it is not needed, but this forces release under high memory pressure.

static VALUE evaporate_bang(VALUE self)
{
        struct raindrops *r = get(self);
        void *addr = r->drops;

        r->drops = MAP_FAILED;
        if (munmap(addr, raindrop_size * r->capa) != 0)
                rb_sys_fail("munmap");
        return Qnil;
}
incr(index[, number]) → result click to toggle source

Increments the value referred to by the index by number. number defaults to 1 if unspecified.

static VALUE incr(int argc, VALUE *argv, VALUE self)
{
        unsigned long nr = incr_decr_arg(argc, argv);

        return ULONG2NUM(__sync_add_and_fetch(addr_of(self, argv[0]), nr));
}
dup → rd_copy click to toggle source

Duplicates and snapshots the current state of a Raindrops object. Even if the given Raindrops object is backed by a file, the copy will be backed by independent, anonymously mapped memory.

static VALUE init_copy(VALUE dest, VALUE source)
{
        struct raindrops *dst = DATA_PTR(dest);
        struct raindrops *src = get(source);

        init_cimpl(dest, SIZET2NUM(src->size), Qnil, Qfalse);
        memcpy(dst->drops, src->drops, raindrop_size * src->size);

        return dest;
}
size → Integer click to toggle source

Returns the number of counters a Raindrops object can hold. Due to page alignment, this is always equal or greater than the number of requested slots passed to Raindrops.new

static VALUE size(VALUE self)
{
        return SIZET2NUM(get(self)->size);
}
size = new_size click to toggle source

Increases or decreases the current capacity of our Raindrop. Raises RangeError if new_size is too big or small for the current backing store

static VALUE setsize(VALUE self, VALUE new_size)
{
        size_t new_rd_size = NUM2SIZET(new_size);
        struct raindrops *r = get(self);

        if (new_rd_size <= r->capa)
                r->size = new_rd_size;
        else
                resize(r, new_rd_size);

        return new_size;
}
to_ary → Array click to toggle source

converts the Raindrops structure to an Array

static VALUE to_ary(VALUE self)
{
        struct raindrops *r = get(self);
        VALUE rv = rb_ary_new2(r->size);
        size_t i;
        unsigned long base = (unsigned long)r->drops;

        for (i = 0; i < r->size; i++) {
                rb_ary_push(rv, ULONG2NUM(*((unsigned long *)base)));
                base += raindrop_size;
        }

        return rv;
}
to_io → IO click to toggle source

Returns the IO object backing the memory for this raindrop, if one was specified when constructing this Raindrop. If this Raindrop is backed by anonymous memory, this method returns nil.

static VALUE to_io(VALUE self)
{
        struct raindrops *r = get(self);
        return r->io;
}

Private Instance Methods

initialize_cimpl(p1, p2, p3) click to toggle source

This is the actual implementation of initialize - the Ruby wrapper handles keyword-argument handling then calls this method.

static VALUE init_cimpl(VALUE self, VALUE size, VALUE io, VALUE zero)
{
        struct raindrops *r = DATA_PTR(self);
        int tries = 1;
        size_t tmp;

        if (r->drops != MAP_FAILED)
                rb_raise(rb_eRuntimeError, "already initialized");

        r->size = NUM2SIZET(size);
        if (r->size < 1)
                rb_raise(rb_eArgError, "size must be >= 1");

        tmp = PAGE_ALIGN(raindrop_size * r->size);
        r->capa = tmp / raindrop_size;
        assert(PAGE_ALIGN(raindrop_size * r->capa) == tmp && "not aligned");

        r->io = io;

retry:
        if (RTEST(r->io)) {
                int fd = NUM2INT(rb_funcall(r->io, rb_intern("fileno"), 0));
                rb_funcall(r->io, rb_intern("truncate"), 1, SIZET2NUM(tmp));
                r->drops = mmap(NULL, tmp,
                                PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
        } else {
                r->drops = mmap(NULL, tmp,
                                PROT_READ|PROT_WRITE, MAP_ANON|MAP_SHARED,
                                -1, 0);
        }
        if (r->drops == MAP_FAILED) {
                int err = errno;

                if ((err == EAGAIN || err == ENOMEM) && tries-- > 0) {
                        rb_gc();
                        goto retry;
                }
                rb_sys_fail("mmap");
        }
        r->pid = getpid();

        if (RTEST(zero))
                memset(r->drops, 0, tmp);

        return self;
}