From 18ee38af90b527f617af7bf9bbcf2e8e7cb0df17 Mon Sep 17 00:00:00 2001 From: KJ Tsanaktsidis Date: Thu, 25 Nov 2021 17:56:19 +1100 Subject: Allow Raindrops objects to be backed by a file Currently, all memory used by Raindrops is mapped as MAP_ANONYMOUS. This means that although Raindrops counters can be shared between processes that have forked from each other, it is not possible to share the counter values with another, unrelated process. This patch adds support for backing the Raindrops mapping with a file descriptor obtained from an IO object. The #initialize API has been enhanced with two new keyword options: Raindrops.new(size, io: nil, zero: false) If an instance of IO is provided, then the underlying file descriptor for that IO will be used to back the memory mapping Raindrops creates. An unrelated process can then open the same file, and read the counters; either by mmap'ing the file itself (or using Raindrops to do so), or by making ordinary seek()/read() calls if performance is not a concern. Note that the provided IO object _must_ implement #truncate; this is used to set the size of the file to be right-sized for the memory mapping that is created. If the zero argument is passed as true, then the mapping will be zero'd by Raindrops as part of its initialization. If it's false, then the Raindrops counters existing in the file will be preserved. This allows counter values to be persisted (although note that Raindrops makes no attempt to msync the values, so they are not durable to e.g. system crashes). Counter values can easily be shared between processes in-memory only without touching the disk by passing in a File on a tmpfs as the io object. --- ext/raindrops/raindrops.c | 63 ++++++++++++++++++++++++++++++++++++----------- 1 file changed, 48 insertions(+), 15 deletions(-) (limited to 'ext') diff --git a/ext/raindrops/raindrops.c b/ext/raindrops/raindrops.c index 837084c..72a6ee7 100644 --- a/ext/raindrops/raindrops.c +++ b/ext/raindrops/raindrops.c @@ -4,6 +4,7 @@ #include #include #include +#include #include "raindrops_atomic.h" #ifndef SIZET2NUM @@ -34,9 +35,17 @@ struct raindrops { size_t size; size_t capa; pid_t pid; + VALUE io; struct raindrop *drops; }; +/* called by GC */ +static void rd_mark(void *ptr) +{ + struct raindrops *r = ptr; + rb_gc_mark(r->io); +} + /* called by GC */ static void rd_free(void *ptr) { @@ -60,7 +69,7 @@ static size_t rd_memsize(const void *ptr) static const rb_data_type_t rd_type = { "raindrops", - { NULL, rd_free, rd_memsize, /* reserved */ }, + { rd_mark, rd_free, rd_memsize, /* reserved */ }, /* parent, data, [ flags ] */ }; @@ -87,16 +96,10 @@ static struct raindrops *get(VALUE self) } /* - * call-seq: - * Raindrops.new(size) -> raindrops object - * - * 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+. + * This is the _actual_ implementation of #initialize - the Ruby wrapper + * handles keyword-argument handling then calls this method. */ -static VALUE init(VALUE self, VALUE size) +static VALUE init_cimpl(VALUE self, VALUE size, VALUE io, VALUE zero) { struct raindrops *r = DATA_PTR(self); int tries = 1; @@ -113,9 +116,19 @@ static VALUE init(VALUE self, VALUE size) r->capa = tmp / raindrop_size; assert(PAGE_ALIGN(raindrop_size * r->capa) == tmp && "not aligned"); + r->io = io; + retry: - r->drops = mmap(NULL, tmp, - PROT_READ|PROT_WRITE, MAP_ANON|MAP_SHARED, -1, 0); + 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; @@ -127,6 +140,9 @@ retry: } r->pid = getpid(); + if (RTEST(zero)) + memset(r->drops, 0, tmp); + return self; } @@ -217,14 +233,16 @@ static VALUE capa(VALUE self) * call-seq: * rd.dup -> rd_copy * - * Duplicates and snapshots the current state of a Raindrops object. + * 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(dest, SIZET2NUM(src->size)); + init_cimpl(dest, SIZET2NUM(src->size), Qnil, Qfalse); memcpy(dst->drops, src->drops, raindrop_size * src->size); return dest; @@ -375,6 +393,20 @@ static VALUE evaporate_bang(VALUE self) return Qnil; } +/* + * call-seq: + * to_io -> IO + * + * 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; +} + void Init_raindrops_ext(void) { VALUE cRaindrops = rb_define_class("Raindrops", rb_cObject); @@ -433,7 +465,7 @@ void Init_raindrops_ext(void) rb_define_alloc_func(cRaindrops, alloc); - rb_define_method(cRaindrops, "initialize", init, 1); + rb_define_private_method(cRaindrops, "initialize_cimpl", init_cimpl, 3); rb_define_method(cRaindrops, "incr", incr, -1); rb_define_method(cRaindrops, "decr", decr, -1); rb_define_method(cRaindrops, "to_ary", to_ary, 0); @@ -444,6 +476,7 @@ void Init_raindrops_ext(void) rb_define_method(cRaindrops, "capa", capa, 0); rb_define_method(cRaindrops, "initialize_copy", init_copy, 1); rb_define_method(cRaindrops, "evaporate!", evaporate_bang, 0); + rb_define_method(cRaindrops, "to_io", to_io, 0); #ifdef __linux__ Init_raindrops_linux_inet_diag(); -- cgit v1.2.3-24-ge0c7