path: root/module/statprof.scm

;;;; (statprof) -- a statistical profiler for Guile
;;;; -*-scheme-*-
;;;;
;;;; 	Copyright (C) 2009, 2010, 2011, 2013-2017  Free Software Foundation, Inc.
;;;;    Copyright (C) 2004, 2009 Andy Wingo <wingo at pobox dot com>
;;;;    Copyright (C) 2001 Rob Browning <rlb at defaultvalue dot org>
;;;; 
;;;; This library is free software; you can redistribute it and/or
;;;; modify it under the terms of the GNU Lesser General Public
;;;; License as published by the Free Software Foundation; either
;;;; version 3 of the License, or (at your option) any later version.
;;;; 
;;;; This library is distributed in the hope that it will be useful,
;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
;;;; Lesser General Public License for more details.
;;;; 
;;;; You should have received a copy of the GNU Lesser General Public
;;;; License along with this library; if not, write to the Free Software
;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
;;;; 


;;; Commentary:
;;;
;;; @code{(statprof)} is a statistical profiler for Guile.  See the
;;; "Statprof" section in the manual, for more information.
;;;
;;; Code:

(define-module (statprof)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-9)
  #:use-module (srfi srfi-9 gnu)
  #:use-module (ice-9 format)
  #:use-module (ice-9 match)
  #:use-module (ice-9 vlist)
  #:use-module (system vm vm)
  #:use-module (system vm frame)
  #:use-module (system vm debug)
  #:use-module (system vm program)
  #:export (statprof-active?
            statprof-start
            statprof-stop
            statprof-reset

            statprof-accumulated-time
            statprof-sample-count
            statprof-fold-call-data
            statprof-proc-call-data
            statprof-call-data-name
            statprof-call-data-calls
            statprof-call-data-cum-samples
            statprof-call-data-self-samples
            statprof-call-data->stats
           
            statprof-stats-proc-name
            statprof-stats-proc-source
            statprof-stats-%-time-in-proc
            statprof-stats-cum-secs-in-proc
            statprof-stats-self-secs-in-proc
            statprof-stats-calls
            statprof-stats-self-secs-per-call
            statprof-stats-cum-secs-per-call

            statprof-display
            statprof-display-anomalies

            statprof-fetch-stacks
            statprof-fetch-call-tree

            statprof
            gcprof))


;;; ~ Implementation notes ~
;;;
;;; Statprof can be divided into two pieces: data collection and data
;;; analysis.
;;;
;;; The data collection runs concurrently with the program, and is
;;; designed to be as cheap as possible.  The main data collection
;;; instrument is the stack sampler, driven by SIGPROF signals that are
;;; scheduled with periodic setitimer calls.  The stack sampler simply
;;; looks at every frame on the stack, and writes a representation of
;;; the frame's procedure into a growable buffer.
;;;
;;; For most frames, this representation is the instruction pointer of
;;; that frame, because it's cheap to get and you can map from
;;; instruction pointer to procedure fairly cheaply.  This won't
;;; distinguish between different closures which share the same code,
;;; but that is usually what we want anyway.
;;;
;;; One case in which we do want to distinguish closures is the case of
;;; primitive procedures.  If slot 0 in the frame is a primitive
;;; procedure, we record the procedure's name into the buffer instead of
;;; the IP.  It's fairly cheap to check whether a value is a primitive
;;; procedure, and then get its name, as its name is stored in the
;;; closure data.  Calling procedure-name in the stack sampler isn't
;;; something you want to do for other kinds of procedures, though, as
;;; that involves grovelling the debug information.
;;;
;;; The other part of data collection is the exact call counter, which
;;; uses the VM's "apply" hook to record each procedure call.
;;; Naturally, this is quite expensive, and it is off by default.
;;; Running code at every procedure call effectively penalizes procedure
;;; calls.  Still, it's useful sometimes.  If the profiler state has a
;;; call-counts table, then calls will be counted.  As with the stack
;;; counter, usually the key in the hash table is the code pointer of
;;; the procedure being called, except for primitive procedures, in
;;; which case it is the name of the primitive.  The call counter can
;;; also see calls of non-programs, for example in the case of
;;; applicable structs.  In that case the key is the procedure itself.
;;;
;;; After collection is finished, the data can be analyzed.  The first
;;; step is usually to run over the stack traces, tabulating sample
;;; counts by procedure; the stack-samples->procedure-data does that.
;;; The result of stack-samples->procedure-data is a hash table mapping
;;; procedures to "call data" records.  The call data values are exposed
;;; to users via the statprof-fold-call-data procedure.
;;;
;;; Usually all the analysis is triggered by calling statprof-display,
;;; or having the statprof procedure call it for you.
;;;
;;; The other thing we can do is to look at the stacks themselves, for
;;; example via statprof-fetch-call-tree.
;;;

;;; ~ Threads and state ~
;;;
;;; The state of the profiler is contained in a <state> record, which is
;;; bound to a thread-local parameter.  The accurate call counter uses
;;; the VM apply hook, which is also local to the current thread, so all
;;; is good there.
;;;
;;; The problem comes in the statistical stack sampler's use of
;;; `setitimer' and SIGPROF.  The timer manipulated by setitimer is a
;;; whole-process timer, so it decrements as other threads execute,
;;; which is the wrong thing if you want to profile just one thread.  On
;;; the other hand, SIGPROF is delivered to the process as a whole,
;;; which is fine given Guile's signal-handling thread, but then only
;;; delivered to the thread running statprof, which isn't the right
;;; thing if you want to profile the whole system.
;;;
;;; The summary is that statprof works more or less well as a per-thread
;;; profiler if no other threads are running on their own when
;;; profiling.  If the other threads are running on behalf of the thread
;;; being profiled (as via futures or parallel marking) things still
;;; mostly work as expected.  You can run statprof in one thread,
;;; finish, and then run statprof in another thread, and the profile
;;; runs won't affect each other.  But if you want true per-thread
;;; profiles when other things are happening in the process, including
;;; other statprof runs, or whole-process profiles with per-thread
;;; breakdowns, the use of setitimer currently prevents that.
;;;
;;; The solution would be to switch to POSIX.1-2001's timer_create(2),
;;; and to add some more threading-related API to statprof.  Some other
;;; day.
;;;

(define-record-type <state>
  (make-state accumulated-time last-start-time sample-count
              sampling-period remaining-prof-time profile-level
              call-counts gc-time-taken inside-profiler?
              prev-sigprof-handler outer-cut buffer buffer-pos)
  state?
  ;; Total time so far.
  (accumulated-time accumulated-time set-accumulated-time!)
  ;; Start-time when timer is active.
  (last-start-time last-start-time set-last-start-time!)
  ;; Total count of sampler calls.
  (sample-count sample-count set-sample-count!)
  ;; Microseconds.
  (sampling-period sampling-period set-sampling-period!)
  ;; Time remaining when prof suspended.
  (remaining-prof-time remaining-prof-time set-remaining-prof-time!)
  ;; For user start/stop nesting.
  (profile-level profile-level set-profile-level!)
  ;; Hash table mapping ip -> call count, or #f if not counting calls.
  (call-counts call-counts set-call-counts!)
  ;; GC time between statprof-start and statprof-stop.
  (gc-time-taken gc-time-taken set-gc-time-taken!)
  ;; True if we are inside the profiler.
  (inside-profiler? inside-profiler? set-inside-profiler?!)
  ;; Previous sigprof handler.
  (prev-sigprof-handler prev-sigprof-handler set-prev-sigprof-handler!)
  ;; Outer stack cut, or 0.
  (outer-cut outer-cut)
  ;; Stack samples.
  (buffer buffer set-buffer!)
  (buffer-pos buffer-pos set-buffer-pos!))

(define profiler-state (make-parameter #f))

(define (fresh-buffer)
  (make-vector 1024 #f))

(define (expand-buffer buf)
  (let* ((size (vector-length buf))
         (new (make-vector (* size 2) #f)))
    (vector-move-left! buf 0 (vector-length buf) new 0)
    new))

(define* (fresh-profiler-state #:key (count-calls? #f)
                               (sampling-period 10000)
                               (outer-cut 0))
  (make-state 0 #f 0
              sampling-period 0 0
              (and count-calls? (make-hash-table)) 0 #f
              #f outer-cut (fresh-buffer) 0))

(define (ensure-profiler-state)
  (or (profiler-state)
      (let ((state (fresh-profiler-state)))
        (profiler-state state)
        state)))

(define (existing-profiler-state)
  (or (profiler-state)
      (error "expected there to be a profiler state")))

(define (accumulate-time state stop-time)
  (set-accumulated-time! state
                         (+ (accumulated-time state)
                            (- stop-time (last-start-time state)))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; SIGPROF handler

(define (sample-stack-procs state stack)
  (set-sample-count! state (+ (sample-count state) 1))

  (let lp ((frame (stack-ref stack 0))
           (len (stack-length stack))
           (buffer (buffer state))
           (pos (buffer-pos state)))
    (define (write-sample sample)
      (vector-set! buffer pos sample))
    (define (continue pos)
      (lp (frame-previous frame) (1- len) buffer pos))
    (define (write-sample-and-continue sample)
      (write-sample sample)
      (continue (1+ pos)))
    (cond
     ((= pos (vector-length buffer))
      (lp frame len (expand-buffer buffer) pos))
     ((or (zero? len) (not frame))
      (write-sample #f)
      (set-buffer! state buffer)
      (set-buffer-pos! state (1+ pos)))
     (else
      (write-sample-and-continue
       (frame-instruction-pointer-or-primitive-procedure-name frame))))))

(define (reset-sigprof-timer usecs)
  ;; Guile's setitimer binding is terrible.
  (let ((prev (setitimer ITIMER_PROF 0 0 0 usecs)))
    (+ (* (caadr prev) #e1e6) (cdadr prev))))

(define profile-signal-handler
  (let ()
    (define (profile-signal-handler sig)
      (define state (existing-profiler-state))

      (set-inside-profiler?! state #t)

      (when (positive? (profile-level state))
        (let* ((stop-time (get-internal-run-time))
               ;; Cut down to the signal handler.  Note that this will
               ;; only work if statprof.scm is compiled; otherwise we
               ;; get `eval' on the stack instead, because if it's not
               ;; compiled, profile-signal-handler is a thunk that
               ;; tail-calls eval.  For the same reason we define the
               ;; handler in an inner letrec, so that the compiler sees
               ;; the inner reference to profile-signal-handler as the
               ;; same as the procedure, and therefore keeps slot 0
               ;; alive.  Nastiness, that.  Finally we cut one more
               ;; inner frame, corresponding to the handle-interrupts
               ;; trampoline.
               (stack
                (or (make-stack #t profile-signal-handler (outer-cut state) 1)
                    (pk 'what! (make-stack #t)))))

          (sample-stack-procs state stack)
          (accumulate-time state stop-time)
          (set-last-start-time! state (get-internal-run-time))

          (reset-sigprof-timer (sampling-period state))))

      (set-inside-profiler?! state #f))
    profile-signal-handler))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Count total calls.

(define (count-call frame)
  (let ((state (existing-profiler-state)))
    (unless (inside-profiler? state)
      (let* ((key (frame-instruction-pointer-or-primitive-procedure-name frame))
             (handle (hashv-create-handle! (call-counts state) key 0)))
        (set-cdr! handle (1+ (cdr handle)))))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(define (statprof-active?)
  "Returns @code{#t} if @code{statprof-start} has been called more times
than @code{statprof-stop}, @code{#f} otherwise."
  (define state (profiler-state))
  (and state (positive? (profile-level state))))

;; Do not call this from statprof internal functions -- user only.
(define* (statprof-start #:optional (state (ensure-profiler-state)))
  "Start the profiler.@code{}"
  ;; After some head-scratching, I don't *think* I need to mask/unmask
  ;; signals here, but if I'm wrong, please let me know.
  (set-profile-level! state (+ (profile-level state) 1))
  (when (= (profile-level state) 1)
    (let ((rpt (remaining-prof-time state)))
      (set-remaining-prof-time! state 0)
      ;; FIXME: Use per-thread run time.
      (set-last-start-time! state (get-internal-run-time))
      (set-gc-time-taken! state (assq-ref (gc-stats) 'gc-time-taken))
      (let ((prev (sigaction SIGPROF profile-signal-handler)))
        (set-prev-sigprof-handler! state (car prev)))
      (reset-sigprof-timer (if (zero? rpt) (sampling-period state) rpt))
      (when (call-counts state)
        (add-hook! (vm-apply-hook) count-call)
        (set-vm-trace-level! (1+ (vm-trace-level))))
      #t)))
  
;; Do not call this from statprof internal functions -- user only.
(define* (statprof-stop #:optional (state (ensure-profiler-state)))
  "Stop the profiler.@code{}"
  ;; After some head-scratching, I don't *think* I need to mask/unmask
  ;; signals here, but if I'm wrong, please let me know.
  (set-profile-level! state (- (profile-level state) 1))
  (when (zero? (profile-level state))
    (when (call-counts state)
      (set-vm-trace-level! (1- (vm-trace-level)))
      (remove-hook! (vm-apply-hook) count-call))
    (set-gc-time-taken! state
                        (- (assq-ref (gc-stats) 'gc-time-taken)
                           (gc-time-taken state)))
    ;; I believe that we need to do this before getting the time
    ;; (unless we want to make things even more complicated).
    (set-remaining-prof-time! state (reset-sigprof-timer 0))
    (accumulate-time state (get-internal-run-time))
    (sigaction SIGPROF (prev-sigprof-handler state))
    (set-prev-sigprof-handler! state #f)
    (set-last-start-time! state #f)))

(define* (statprof-reset sample-seconds sample-microseconds count-calls?
                         #:optional full-stacks?)
  "Reset the statprof sampler interval to @var{sample-seconds} and
@var{sample-microseconds}. If @var{count-calls?} is true, arrange to
instrument procedure calls as well as collecting statistical profiling
data.  (The optional @var{full-stacks?} argument is deprecated; statprof
always collects full stacks.)"
  (when (statprof-active?)
    (error "Can't reset profiler while profiler is running."))
  (profiler-state
   (fresh-profiler-state #:count-calls? count-calls?
                         #:sampling-period (+ (* sample-seconds #e1e6)
                                              sample-microseconds)))
  (values))

(define-record-type call-data
  (make-call-data name printable source
                  call-count cum-sample-count self-sample-count)
  call-data?
  (name call-data-name)
  (printable call-data-printable)
  (source call-data-source)
  (call-count call-data-call-count set-call-data-call-count!)
  (cum-sample-count call-data-cum-sample-count set-call-data-cum-sample-count!)
  (self-sample-count call-data-self-sample-count set-call-data-self-sample-count!))

(define (source->string source)
  (format #f "~a:~a:~a"
          (or (source-file source) "<current input>")
          (source-line-for-user source)
          (source-column source)))

(define (program-debug-info-printable pdi)
  (let* ((addr (program-debug-info-addr pdi))
         (name (or (and=> (program-debug-info-name pdi) symbol->string)
                   (string-append "#x" (number->string addr 16))))
         (loc (and=> (find-source-for-addr addr) source->string)))
    (if loc
        (string-append name " at " loc)
        name)))

(define (addr->pdi addr cache)
  (cond
   ((hashv-get-handle cache addr) => cdr)
   (else
    (let ((data (find-program-debug-info addr)))
      (hashv-set! cache addr data)
      data))))

(define (addr->printable addr pdi)
  (or (and=> (and=> pdi program-debug-info-name) symbol->string)
      (string-append "anon #x" (number->string addr 16))))

(define (inc-call-data-cum-sample-count! cd)
  (set-call-data-cum-sample-count! cd (1+ (call-data-cum-sample-count cd))))
(define (inc-call-data-self-sample-count! cd)
  (set-call-data-self-sample-count! cd (1+ (call-data-self-sample-count cd))))

(define (skip-count-call buffer start len)
  ;; If we are counting all procedure calls, count-call might be on the
  ;; stack.  If it is, skip that part of the stack.
  (match (program-address-range count-call)
    ((lo . hi)
     (let lp ((pos start))
       (if (< pos len)
           (let ((key (vector-ref buffer pos)))
             (cond
              ((not key)
               ;; End of stack; count-call not on the stack.
               start)
              ((and (number? key) (<= lo key) (< key hi))
               ;; Found count-call.
               (1+ pos))
              (else
               ;; Otherwise keep going.
               (lp (1+ pos)))))
           start)))))

(define (stack-samples->procedure-data state)
  (let ((table (make-hash-table))
        (addr-cache (make-hash-table))
        (call-counts (call-counts state))
        (buffer (buffer state))
        (len (buffer-pos state)))
    (define (addr->call-data addr)
      (let* ((pdi (addr->pdi addr addr-cache))
             (entry (if pdi (program-debug-info-addr pdi) addr)))
        (or (hashv-ref table entry)
            (let ((data (make-call-data (and=> pdi program-debug-info-name)
                                        (addr->printable entry pdi)
                                        (find-source-for-addr entry)
                                        (and call-counts
                                             (hashv-ref call-counts entry))
                                        0
                                        0)))
              (hashv-set! table entry data)
              data))))

    (define (callee->call-data callee)
      (cond
       ((number? callee) (addr->call-data callee))
       ((hashv-ref table callee))
       (else
        (let ((data (make-call-data
                     (cond ((procedure? callee) (procedure-name callee))
                           ;; a primitive
                           ((symbol? callee) callee)
                           (else #f))
                     (with-output-to-string (lambda () (write callee)))
                     #f
                     (and call-counts (hashv-ref call-counts callee))
                     0
                     0)))
          (hashv-set! table callee data)
          data))))

    (when call-counts
      (hash-for-each (lambda (callee count)
                       (callee->call-data callee))
                     call-counts))

    (let visit-stacks ((pos 0))
      (cond
       ((< pos len)
        (let ((pos (if call-counts
                       (skip-count-call buffer pos len)
                       pos)))
          (inc-call-data-self-sample-count!
           (callee->call-data (vector-ref buffer pos)))
          (let visit-stack ((pos pos))
            (cond
             ((vector-ref buffer pos)
              => (lambda (callee)
                   (inc-call-data-cum-sample-count! (callee->call-data callee))
                   (visit-stack (1+ pos))))
             (else
              (visit-stacks (1+ pos)))))))
       (else table)))))

(define (stack-samples->callee-lists state)
  (let ((buffer (buffer state))
        (len (buffer-pos state)))
    (let visit-stacks ((pos 0) (out '()))
      (cond
       ((< pos len)
        (let visit-stack ((pos (if (call-counts state)
                                   (skip-count-call buffer pos len)
                                   pos))
                          (stack '()))
          (cond
           ((vector-ref buffer pos)
            => (lambda (callee)
                 (visit-stack (1+ pos) (cons callee stack))))
           (else
            (visit-stacks (1+ pos) (cons (reverse stack) out))))))
       (else (reverse out))))))

(define* (statprof-fold-call-data proc init #:optional
                                  (state (existing-profiler-state)))
  "Fold @var{proc} over the call-data accumulated by statprof. Cannot be
called while statprof is active. @var{proc} should take two arguments,
@code{(@var{call-data} @var{prior-result})}.

Note that a given proc-name may appear multiple times, but if it does,
it represents different functions with the same name."
  (when (statprof-active?)
    (error "Can't call statprof-fold-call-data while profiler is running."))
  (hash-fold
   (lambda (key value prior-result)
     (proc value prior-result))
   init
   (stack-samples->procedure-data state)))

(define* (statprof-proc-call-data proc #:optional
                                  (state (existing-profiler-state)))
  "Returns the call-data associated with @var{proc}, or @code{#f} if
none is available."
  (when (statprof-active?)
    (error "Can't call statprof-proc-call-data while profiler is running."))
  (unless (program? proc)
    (error "statprof-call-data only works for VM programs"))
  (let* ((code (program-code proc))
         (key (if (primitive-code? code)
                  (procedure-name proc)
                  code)))
    (hashv-ref (stack-samples->procedure-data state) key)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Stats

(define-record-type stats
  (make-stats proc-name proc-source
              %-time-in-proc cum-secs-in-proc self-secs-in-proc
              calls)
  stats?
  (proc-name statprof-stats-proc-name)
  (proc-source statprof-stats-proc-source)
  (%-time-in-proc statprof-stats-%-time-in-proc)
  (cum-secs-in-proc statprof-stats-cum-secs-in-proc)
  (self-secs-in-proc statprof-stats-self-secs-in-proc)
  (calls statprof-stats-calls))

(define (statprof-stats-self-secs-per-call stats)
  (let ((calls (statprof-stats-calls stats)))
    (and calls
         (/ (statprof-stats-self-secs-in-proc stats)
            calls))))

(define (statprof-stats-cum-secs-per-call stats)
  (let ((calls (statprof-stats-calls stats)))
    (and calls
         (/ (statprof-stats-cum-secs-in-proc stats)
            ;; `calls' might be 0 if we entered statprof during the
            ;; dynamic extent of the call.
            (max calls 1)))))

(define (statprof-call-data->stats call-data)
  "Returns an object of type @code{statprof-stats}."
  (define state (existing-profiler-state))

  (let* ((proc-name (call-data-name call-data))
         (proc-source (and=> (call-data-source call-data) source->string))
         (self-samples (call-data-self-sample-count call-data))
         (cum-samples (call-data-cum-sample-count call-data))
         (all-samples (statprof-sample-count state))
         (secs-per-sample (/ (statprof-accumulated-time state)
                             (statprof-sample-count state)))
         (num-calls (and (call-counts state)
                         (statprof-call-data-calls call-data))))

    (make-stats (or proc-name
                    ;; If there is no name and no source, fall back to
                    ;; printable.
                    (and (not proc-source) (call-data-printable call-data)))
                proc-source
                (* (/ self-samples all-samples) 100.0)
                (* cum-samples secs-per-sample 1.0)
                (* self-samples secs-per-sample 1.0)
                num-calls)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(define (stats-sorter x y)
  (let ((diff (- (statprof-stats-self-secs-in-proc x)
                 (statprof-stats-self-secs-in-proc y))))
    (positive?
     (if (= diff 0)
         (- (statprof-stats-cum-secs-in-proc x)
            (statprof-stats-cum-secs-in-proc y))
         diff))))

(define* (statprof-display/flat port state)
  "Displays a gprof-like summary of the statistics collected. Unless an
optional @var{port} argument is passed, uses the current output port."
  (cond
   ((zero? (statprof-sample-count state))
    (format port "No samples recorded.\n"))
   (else
    (let* ((stats-list (statprof-fold-call-data
                        (lambda (data prior-value)
                          (cons (statprof-call-data->stats data)
                                prior-value))
                        '()
                        state))
           (sorted-stats (sort stats-list stats-sorter)))

      (define (display-stats-line stats)
        (format port "~6,2f ~9,2f ~9,2f"
                (statprof-stats-%-time-in-proc stats)
                (statprof-stats-cum-secs-in-proc stats)
                (statprof-stats-self-secs-in-proc stats))
        (if (call-counts state)
            (if (statprof-stats-calls stats)
                (format port " ~7d  "
                        (statprof-stats-calls stats))
                (format port "                            "))
            (display "  " port))
        (let ((source (statprof-stats-proc-source stats))
              (name (statprof-stats-proc-name stats)))
          (when source
            (display source port)
            (when name
              (display ":" port)))
          (when name
            (display name port))
          (newline port)))
    
      (if (call-counts state)
          (begin
            (format  port "~5a ~10a   ~7a  ~8a\n"
                     "%  " "cumulative" "self" "")
            (format  port "~5a  ~9a  ~8a  ~7a ~a\n"
                     "time" "seconds" "seconds" "calls" "procedure"))
          (begin
            (format  port "~5a ~10a   ~7a  ~8a\n"
                     "%" "cumulative" "self" "")
            (format  port "~5a  ~10a  ~7a  ~a\n"
                     "time" "seconds" "seconds" "procedure")))

      (for-each display-stats-line sorted-stats)

      (display "---\n" port)
      (format port "Sample count: ~A\n" (statprof-sample-count state))
      (format port "Total time: ~A seconds (~A seconds in GC)\n"
              (statprof-accumulated-time state)
              (/ (gc-time-taken state)
                 1.0 internal-time-units-per-second))))))

(define* (statprof-display-anomalies #:optional (state
                                                 (existing-profiler-state)))
  "A sanity check that attempts to detect anomalies in statprof's
statistics.@code{}"
  (statprof-fold-call-data
   (lambda (data prior-value)
     (when (and (call-counts state)
                (zero? (call-data-call-count data))
                (positive? (call-data-cum-sample-count data)))
       (format #t
               "==[~A ~A ~A]\n"
               (call-data-name data)
               (call-data-call-count data)
               (call-data-cum-sample-count data))))
   #f
   state)
  (format #t "Total time: ~A\n" (statprof-accumulated-time state))
  (format #t "Sample count: ~A\n" (statprof-sample-count state)))

(define* (statprof-accumulated-time #:optional (state
                                                (existing-profiler-state)))
  "Returns the time accumulated during the last statprof run.@code{}"
  (/ (accumulated-time state) 1.0 internal-time-units-per-second))

(define* (statprof-sample-count #:optional (state (existing-profiler-state)))
  "Returns the number of samples taken during the last statprof run.@code{}"
  (sample-count state))

(define statprof-call-data-name call-data-name)
(define statprof-call-data-calls call-data-call-count)
(define statprof-call-data-cum-samples call-data-cum-sample-count)
(define statprof-call-data-self-samples call-data-self-sample-count)

(define* (statprof-fetch-stacks #:optional (state (existing-profiler-state)))
  "Returns a list of stacks, as they were captured since the last call
to @code{statprof-reset}."
  (stack-samples->callee-lists state))

;; tree ::= (car n . tree*)

(define (lists->trees lists equal?)
  (let lp ((in lists) (n-terminal 0) (tails '()))
    (cond
     ((null? in)
      (let ((trees (map (lambda (tail)
                          (cons (car tail)
                                (lists->trees (cdr tail) equal?)))
                        tails)))
        (cons (apply + n-terminal (map cadr trees))
              (sort trees
                    (lambda (a b) (> (cadr a) (cadr b)))))))
     ((null? (car in))
      (lp (cdr in) (1+ n-terminal) tails))
     ((find (lambda (x) (equal? (car x) (caar in)))
            tails)
      => (lambda (tail)
           (lp (cdr in)
               n-terminal
               (assq-set! tails
                          (car tail)
                          (cons (cdar in) (cdr tail))))))
     (else
      (lp (cdr in)
          n-terminal
          (acons (caar in) (list (cdar in)) tails))))))

(define (collect-cycles items)
  (define (find-cycle item stack)
    (match (vhash-assoc item stack)
      (#f #f)
      ((_ . pos)
       (let ((size (- (vlist-length stack) pos)))
         (and (<= (1- (* size 2)) (vlist-length stack))
              (let lp ((i 0))
                (if (= i (1- size))
                    size
                    (and (equal? (car (vlist-ref stack i))
                                 (car (vlist-ref stack (+ i size))))
                         (lp (1+ i))))))))))
  (define (collect-cycle stack size)
    (vlist-fold-right (lambda (pair cycle)
                        (cons (car pair) cycle))
                      '()
                      (vlist-take stack size)))
  (define (detect-cycle items stack)
    (match items
      (() stack)
      ((item . items)
       (let* ((cycle-size (find-cycle item stack)))
         (if cycle-size
             (chomp-cycles (collect-cycle stack cycle-size)
                           items
                           (vlist-drop stack (1- (* cycle-size 2))))
             (chomp-cycles (list item) items stack))))))
  (define (skip-cycles cycle items)
    (let lp ((a cycle) (b items))
      (match a
        (() (skip-cycles cycle b))
        ((a . a*)
         (match b
           (() items)
           ((b . b*)
            (if (equal? a b)
                (lp a* b*)
                items)))))))
  (define (chomp-cycles cycle items stack)
    (detect-cycle (skip-cycles cycle items)
                  (vhash-cons (match cycle
                                ((item) item)
                                (cycle cycle))
                              (vlist-length stack)
                              stack)))
  (vlist-fold
   (lambda (pair out)
     (cons (car pair) out))
   '()
   (detect-cycle items vlist-null)))

(define* (statprof-fetch-call-tree #:optional (state (existing-profiler-state))
                                   #:key precise?)
  "Return a call tree for the previous statprof run.

The return value is a list of nodes, each of which is of the type:
@code
 node ::= (@var{proc} @var{count} . @var{nodes})
@end code"
  (define-syntax-rule (define-memoized (fn arg) body)
    (define fn
      (let ((table (make-hash-table)))
        (lambda (arg)
          (cond
           ((hash-get-handle table arg) => cdr)
           (else
            (let ((res body))
              (hash-set! table arg res)
              res)))))))
  (define-memoized (callee->printable callee)
    (cond
     ((number? callee)
      (let* ((pdi (find-program-debug-info callee))
             (name (or (and=> (and pdi (program-debug-info-name pdi))
                              symbol->string)
                       (string-append "#x" (number->string callee 16))))
             (loc (and=> (find-source-for-addr
                          (or (and (not precise?)
                                   (and=> pdi program-debug-info-addr))
                              callee))
                         source->string)))
        (if loc
            (string-append name " at " loc)
            name)))
     (else
      (with-output-to-string (lambda () (write callee))))))
  (define (munge-stack stack)
    ;; We collect the sample in newest-to-oldest
    ;; order.  Change to have the oldest first.
    (let ((stack (reverse stack)))
      (define (cycle->printable item)
        (if (string? item)
            item
            (string-join (map cycle->printable item) ", ")))
      (map cycle->printable (collect-cycles (map callee->printable stack)))))
  (let ((stacks (map munge-stack (stack-samples->callee-lists state))))
    (cons #t (lists->trees stacks equal?))))

(define (statprof-display/tree port state)
  (match (statprof-fetch-call-tree state)
    ((#t total-count . trees)
     (define (print-tree tree indent)
       (define (print-subtree tree) (print-tree tree (+ indent 2)))
       (match tree
         ((callee count . trees)
          (format port "~vt~,1f% ~a\n" indent (* 100. (/ count total-count))
                  callee)
          (for-each print-subtree trees))))
     (for-each (lambda (tree) (print-tree tree 0)) trees)))
  (display "---\n" port)
  (format port "Sample count: ~A\n" (statprof-sample-count state))
  (format port "Total time: ~A seconds (~A seconds in GC)\n"
          (statprof-accumulated-time state)
          (/ (gc-time-taken state)
             1.0 internal-time-units-per-second)))

(define* (statprof-display #:optional (port (current-output-port))
                           (state (existing-profiler-state))
                           #:key (style 'flat))
  "Displays a summary of the statistics collected. Unless an optional
@var{port} argument is passed, uses the current output port."
  (case style
    ((flat) (statprof-display/flat port state))
    ((anomalies)
     (with-output-to-port port
       (lambda ()
         (statprof-display-anomalies state))))
    ((tree) (statprof-display/tree port state))
    (else (error "Unknown statprof display style" style))))

(define (call-thunk thunk)
  (call-with-values (lambda () (thunk))
    (lambda results
      (apply values results))))

(define* (statprof thunk #:key (loop 1) (hz 100) (count-calls? #f)
                   (port (current-output-port)) full-stacks?
                   (display-style 'flat))
  "Profile the execution of @var{thunk}, and return its return values.

The stack will be sampled @var{hz} times per second, and the thunk
itself will be called @var{loop} times.

If @var{count-calls?} is true, all procedure calls will be recorded. This
operation is somewhat expensive."
  
  (let ((state (fresh-profiler-state #:count-calls? count-calls?
                                     #:sampling-period
                                     (inexact->exact (round (/ 1e6 hz)))
                                     #:outer-cut
                                     (program-address-range call-thunk))))
    (parameterize ((profiler-state state))
      (dynamic-wind
        (lambda ()
          (statprof-start state))
        (lambda ()
          (let lp ((i loop))
            (unless (= i 1)
              (call-thunk thunk)
              (lp (1- i))))
          (call-thunk thunk))
        (lambda ()
          (statprof-stop state)
          (statprof-display port state #:style display-style))))))

(define* (gcprof thunk #:key (loop 1) full-stacks? (port (current-output-port)))
  "Do an allocation profile of the execution of @var{thunk}.

The stack will be sampled soon after every garbage collection, yielding
an approximate idea of what is causing allocation in your program.

Since GC does not occur very frequently, you may need to use the
@var{loop} parameter, to cause @var{thunk} to be called @var{loop}
times."
  
  (let ((state (fresh-profiler-state #:outer-cut
                                     (program-address-range call-thunk))))
    (parameterize ((profiler-state state))
      (define (gc-callback)
        (unless (inside-profiler? state)
          (set-inside-profiler?! state #t)

          (let ((stop-time (get-internal-run-time))
                ;; Cut down to gc-callback, and then two more (the
                ;; after-gc async and the handle-interrupts trampoline).
                ;; See the note in profile-signal-handler also.
                (stack (or (make-stack #t gc-callback (outer-cut state) 2)
                           (pk 'what! (make-stack #t)))))
            (sample-stack-procs state stack)
            (accumulate-time state stop-time)
            (set-last-start-time! state (get-internal-run-time)))

          (set-inside-profiler?! state #f)))

      (dynamic-wind
        (lambda ()
          (set-profile-level! state 1)
          (set-last-start-time! state (get-internal-run-time))
          (set-gc-time-taken! state (assq-ref (gc-stats) 'gc-time-taken))
          (add-hook! after-gc-hook gc-callback))
        (lambda ()
          (let lp ((i loop))
            (unless (zero? i)
              (call-thunk thunk)
              (lp (1- i)))))
        (lambda ()
          (remove-hook! after-gc-hook gc-callback)
          (set-gc-time-taken! state
                              (- (assq-ref (gc-stats) 'gc-time-taken)
                                 (gc-time-taken state)))
          (accumulate-time state (get-internal-run-time))
          (set-profile-level! state 0)
          (statprof-display port state))))))