Upstream: smooth weighted round-robin balancing. For edge case weights like { 5, 1, 1 } we now produce { a, a, b, a, c, a, a } sequence instead of { c, b, a, a, a, a, a } produced previously. Algorithm is as follows: on each peer selection we increase current_weight of each eligible peer by its weight, select peer with greatest current_weight and reduce its current_weight by total number of weight points distributed among peers. In case of { 5, 1, 1 } weights this gives the following sequence of current_weight's: a b c 0 0 0 (initial state) 5 1 1 (a selected) -2 1 1 3 2 2 (a selected) -4 2 2 1 3 3 (b selected) 1 -4 3 6 -3 4 (a selected) -1 -3 4 4 -2 5 (c selected) 4 -2 -2 9 -1 -1 (a selected) 2 -1 -1 7 0 0 (a selected) 0 0 0 To preserve weight reduction in case of failures the effective_weight variable was introduced, which usually matches peer's weight, but is reduced temporarily on peer failures. This change also fixes loop with backup servers and proxy_next_upstream http_404 (ticket #47), and skipping alive upstreams in some cases if there are multiple dead ones (ticket #64).

/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#ifndef _NGX_SLAB_H_INCLUDED_
#define _NGX_SLAB_H_INCLUDED_


#include <ngx_config.h>
#include <ngx_core.h>


typedef struct ngx_slab_page_s  ngx_slab_page_t;

struct ngx_slab_page_s {
    uintptr_t         slab;
    ngx_slab_page_t  *next;
    uintptr_t         prev;
};


typedef struct {
    ngx_shmtx_sh_t    lock;

    size_t            min_size;
    size_t            min_shift;

    ngx_slab_page_t  *pages;
    ngx_slab_page_t   free;

    u_char           *start;
    u_char           *end;

    ngx_shmtx_t       mutex;

    u_char           *log_ctx;
    u_char            zero;

    void             *data;
    void             *addr;
} ngx_slab_pool_t;


void ngx_slab_init(ngx_slab_pool_t *pool);
void *ngx_slab_alloc(ngx_slab_pool_t *pool, size_t size);
void *ngx_slab_alloc_locked(ngx_slab_pool_t *pool, size_t size);
void ngx_slab_free(ngx_slab_pool_t *pool, void *p);
void ngx_slab_free_locked(ngx_slab_pool_t *pool, void *p);


#endif /* _NGX_SLAB_H_INCLUDED_ */