bug#36487: Evaluations do not complete since commit c30d117822a8ca26cd8c06c0a3974955bef68eac

[Ludovic Courtès]

Ludovic Courtès <address@hidden> skribis:

> #104 0x00007fc5247f3a92 in scm_hash_fn_ref () from 
> /gnu/store/r658y3cgpnf99nxjxqgjiaizx20ac4k0-guile-2.2.4/lib/libguile-2.2.so.1
> #105 0x00007fc524859715 in vm_regular_engine () from 
> /gnu/store/r658y3cgpnf99nxjxqgjiaizx20ac4k0-guile-2.2.4/lib/libguile-2.2.so.1
> #106 0x00007fc52485cd6a in scm_call_n () from 
> /gnu/store/r658y3cgpnf99nxjxqgjiaizx20ac4k0-guile-2.2.4/lib/libguile-2.2.so.1
> #107 0x00007fc5247e0da7 in scm_primitive_eval () from 
> /gnu/store/r658y3cgpnf99nxjxqgjiaizx20ac4k0-guile-2.2.4/lib/libguile-2.2.so.1
>
>
> and with debugging symbols:
>
> #3  0x00007fc5247ddc23 in scm_equal_p 
> (x=x@entry="/gnu/store/djh3drjx3hnxlx1bsdnixdm3xjbg5v2c-guile-bootstrap-2.0/bin/guile",
>  
>     
> y=y@entry="/gnu/store/djh3drjx3hnxlx1bsdnixdm3xjbg5v2c-guile-bootstrap-2.0/bin/guile")
>  at eq.c:290
> #4  0x00007fc52484891b in scm_i_struct_equalp (s1="#<struct <derivation>>" = 
> {...}, s2="#<struct <derivation>>" = {...}) at struct.c:693
> #5  0x00007fc52484891b in scm_i_struct_equalp (s1="#<struct 
> <derivation-input>>" = {...}, s2="#<struct <derivation-input>>" = {...}) at 
> struct.c:693
> #6  0x00007fc5247ddc82 in scm_equal_p (
>     x=(#<struct <derivation-input> #<struct <derivation> (("out" . #<struct 
> <derivation-output> 
> "/gnu/store/jc5q4i55hrilibrmacs38skk3cpg2zyb-glibc-bootstrap-0" #f #f #f 
> 3ade740>)) (#<struct <derivation-input> #<struct <derivation> (("out" . 
> #<struct <derivation-output> 
> "/gnu/store/nbi0mzk1dw37nnnahw9akn3bwzwi4gdk-module-import-compiled" #f #f #f 
> 3ae6e00>)) (#<struct <derivation-input> #<struct <derivation> (("out" . 
> #<struct <derivation-output> 
> "/gnu/store/djh3drjx3hnxlx1bsdnixdm3xjbg5v2c-guile-bootstrap-2.0" #f #f #f 
> 3af1b40>)) (#<struct <derivation-input> #<struct <derivation> (("out" . 
> #<struct <derivation-output> 
> "/gnu/store/dgncc5wmw8prxq09y71hqjc6g7rxqvvb-guile-2.0.9.tar.xz" sha256 
> #vu8(183 87 205 70 191 19 236 172 131 251 142 149 95 181 0 150 172 45 23 187 
> 97 12 168 235 129 111 41 48 42 0 168 70) #f 3af10c0>)) () 
> ("/gnu/store/7f1alh9qj2h0wwy2220npgnmw6pbrkwx-mirrors" 
> "/gnu/store/vwyxp1dq4lb97n6b20w5cqxasy2dai79-content-addressed-mirrors") 
> "i686-linux" "builtin:download" () (("content-addressed-mirrors" . 
> "/gnu/store/vwyxp1dq4lb97n6b20w5cqxasy2dai79-content-addressed-mirrors") 
> ("impureEnvVars" . "http_proxy https_proxy LC_ALL LC_MESSAGES LANG COLUMNS") 
> ("mirrors" . "/gnu/store/7f1alh9qj2h0wwy2220npgnmw6pbrkwx-mirrors") ("out" . 
> "/gnu/store/dgncc5wmw8prxq09y71hqjc6g7rxqvvb-guile-2.0.9.tar.xz") 
> ("preferLocalBuild" . "1") ("url" . 
> "(\"https://alpha.gnu.org/gnu/guix/bootstrap/i686-linux/20131110/guile-2.0.9.tar.xz\";
>  
> \"http://alpha.gnu.org/gnu/guix/bootstrap/i686-linux/20131110/guile-2.0.9.tar.xz\";
>  
> \"ftp://alpha.gnu.org/gnu/guix/bootstrap/i686-linux/20131110/guile-2.0.9.tar.xz\";
>  
> \"http://www.fdn.fr/~lcourtes/software/guix/packages/i686-linux/20131110/guile-2.0.9.tar.xz\";
>  
> \"http://flashner.co.il/guix/bootstrap/i686-linux/20131110/guile-2.0.9.tar.xz\";)"))
>  "/gnu/store/jagg4l53ar1m4hsgqlpisw9i4rq2whzd-guile-2.0.9.tar.xz.drv" 
> 3af14e0> ("out") 3af1780>) 
> ("/gnu/store/d32948vi9bs5mmbnvlczqcgwwdqvygiw-build-bootstrap-guile.sh" 
> "/gnu/store/mzfkrxd4w8vqrmyrx169wj8wyw7r8i37-bash") "i686-linux" 
> "/gnu/store/mzfkrxd4w8 […]
>
> So this process is busy comparing deep structures, probably as a
> consequence of 5cf4b26d52bcea382d98fb4becce89be9ee37b55.

With some debugging, I found that the pathological behavior comes from
the memoization hash table of ‘derivation->bytevector’, specifically
after ‘invalidate-derivation-caches!’ has been called.

Namely, after ‘invalidate-derivation-caches!’ has been called, that hash
table has 24K buckets, including 72 buckets of size 6 or more.  One
bucket has 18 entries, which are all alike:

  #<derivation #f => /gnu/store/…-module-import-compiled 94283c0>

The ‘equal?’ calls come from those buckets, and each of them involves
traversing the whole <derivation> tree.

I’m looking for a workaround.

Ludo’.

PS: Below is some debugging code.

(use-modules (system foreign)
             (ice-9 match))

;;       typedef struct {
;;    0    scm_t_weak_entry **buckets;   /* the data */
;;    8    scm_i_pthread_mutex_t lock;   /* the lock */
;;   48    scm_t_weak_table_kind kind;   /* what kind of table it is */
;;   56    unsigned long n_buckets;     /* total number of buckets. */
;;   64    unsigned long n_items;       /* number of items in table */
;;   72    unsigned long lower;         /* when to shrink */
;;   80    unsigned long upper;         /* when to grow */
;;   88    int size_index;              /* index into hashtable_size */
;;   92    int min_size_index;          /* minimum size_index */
;;   96    GC_word last_gc_no;
;;       } scm_t_weak_table;

(define (weak-table-data table)
  "Return an alist describing TABLE."
  (unless (or (weak-key-hash-table? table)
              (weak-value-hash-table? table))
    (error "wrong type argument" table))

  (let* ((address (object-address table))
         (ptr     (dereference-pointer
                   (make-pointer (+ address 8)))))
    (match (parse-c-struct (make-pointer (+ (pointer-address ptr) 48))
                           (list int
                                 unsigned-long unsigned-long
                                 unsigned-long unsigned-long
                                 int
                                 int
                                 unsigned-long))
      ((kind buckets items lower upper size-index min-size-index last-gc-no)
       `((kind . ,kind) (items . ,items) (buckets . ,buckets)
         (lower . ,lower) (upper . ,upper)
         (size-index . ,size-index) (min-size-index . ,min-size-index)
         (last-gc-no . ,last-gc-no))))))

;; typedef struct scm_t_hashtable {
;;   unsigned long n_items;     /* number of items in table */
;;   unsigned long lower;               /* when to shrink */
;;   unsigned long upper;               /* when to grow */
;;   int size_index;            /* index into hashtable_size */
;;   int min_size_index;                /* minimum size_index */
;;   scm_t_hash_fn hash_fn;  /* for rehashing after a GC. */
;; } scm_t_hashtable;

(define (hash-table-data table)
  (unless (hash-table? table)
    (error "wrong type argument" table))

  (let* ((address (object-address table))
         (ptr     (dereference-pointer
                   (make-pointer (+ address (* 2 (sizeof '*)))))))
    (match (parse-c-struct ptr
                           (list unsigned-long
                                 unsigned-long unsigned-long
                                 int
                                 int))
      ((items lower upper size-index min-size-index)
       `((items . ,items)
         (lower . ,lower) (upper . ,upper)
         (size-index . ,size-index) (min-size-index . ,min-size-index))))))

(define (hash-table-buckets table)
  (unless (hash-table? table)
    (error "wrong type argument" table))

  (let* ((address (object-address table))
         (ptr     (dereference-pointer
                   (make-pointer (+ address (* 1 (sizeof '*)))))))
    (pointer->scm ptr)))

(define (hash-table-bucket-sizes table)
  (let ((buckets (hash-table-buckets table)))
    (let loop ((index 0)
               (result '()))
      (if (< index (vector-length buckets))
          (loop (+ 1 index)
                (cons (length (vector-ref buckets index))
                      result))
          (reverse result)))))