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@librelist.org
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.
Public Class Methods
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
.
static VALUE init(VALUE self, VALUE size) { 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"); retry: r->drops = mmap(NULL, tmp, PROT_READ|PROT_WRITE, MAP_ANON|MAP_SHARED, -1, 0); if (r->drops == MAP_FAILED) { if ((errno == EAGAIN || errno == ENOMEM) && tries-- > 0) { rb_gc(); goto retry; } rb_sys_fail("mmap"); } r->pid = getpid(); return self; }
Public Instance Methods
Returns the value of the slot designated by index
static VALUE aref(VALUE self, VALUE index) { return ULONG2NUM(*addr_of(self, index)); }
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; }
Returns the number of slots allocated (but not necessarily used) by the Raindrops object.
static VALUE capa(VALUE self) { return SIZET2NUM(get(self)->capa); }
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)); }
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; }
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)); }
Duplicates and snapshots the current state of a Raindrops object.
static VALUE init_copy(VALUE dest, VALUE source) { struct raindrops *dst = DATA_PTR(dest); struct raindrops *src = get(source); init(dest, SIZET2NUM(src->size)); memcpy(dst->drops, src->drops, raindrop_size * src->size); return dest; }
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; }
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; }