summaryrefslogtreecommitdiff
path: root/mjit_worker.c
blob: 4a7d47c815df8def7e63af0ec5be03dc1bd9cdc0 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
/**********************************************************************

  mjit_worker.c - Worker for MRI method JIT compiler

  Copyright (C) 2017 Vladimir Makarov <vmakarov@redhat.com>.

**********************************************************************/

// NOTE: All functions in this file are executed on MJIT worker. So don't
// call Ruby methods (C functions that may call rb_funcall) or trigger
// GC (using ZALLOC, xmalloc, xfree, etc.) in this file.

/* We utilize widely used C compilers (GCC and LLVM Clang) to
   implement MJIT.  We feed them a C code generated from ISEQ.  The
   industrial C compilers are slower than regular JIT engines.
   Generated code performance of the used C compilers has a higher
   priority over the compilation speed.

   So our major goal is to minimize the ISEQ compilation time when we
   use widely optimization level (-O2).  It is achieved by

   o Using a precompiled version of the header
   o Keeping all files in `/tmp`.  On modern Linux `/tmp` is a file
     system in memory. So it is pretty fast
   o Implementing MJIT as a multi-threaded code because we want to
     compile ISEQs in parallel with iseq execution to speed up Ruby
     code execution.  MJIT has one thread (*worker*) to do
     parallel compilations:
      o It prepares a precompiled code of the minimized header.
        It starts at the MRI execution start
      o It generates PIC object files of ISEQs
      o It takes one JIT unit from a priority queue unless it is empty.
      o It translates the JIT unit ISEQ into C-code using the precompiled
        header, calls CC and load PIC code when it is ready
      o Currently MJIT put ISEQ in the queue when ISEQ is called
      o MJIT can reorder ISEQs in the queue if some ISEQ has been called
        many times and its compilation did not start yet
      o MRI reuses the machine code if it already exists for ISEQ
      o The machine code we generate can stop and switch to the ISEQ
        interpretation if some condition is not satisfied as the machine
        code can be speculative or some exception raises
      o Speculative machine code can be canceled.

   Here is a diagram showing the MJIT organization:

                 _______
                |header |
                |_______|
                    |                         MRI building
      --------------|----------------------------------------
                    |                         MRI execution
                    |
       _____________|_____
      |             |     |
      |          ___V__   |  CC      ____________________
      |         |      |----------->| precompiled header |
      |         |      |  |         |____________________|
      |         |      |  |              |
      |         | MJIT |  |              |
      |         |      |  |              |
      |         |      |  |          ____V___  CC  __________
      |         |______|----------->| C code |--->| .so file |
      |                   |         |________|    |__________|
      |                   |                              |
      |                   |                              |
      | MRI machine code  |<-----------------------------
      |___________________|             loading

*/

#ifdef __sun
#define __EXTENSIONS__ 1
#endif

#include "vm_core.h"
#include "mjit.h"
#include "gc.h"
#include "ruby_assert.h"
#include "ruby/debug.h"
#include "ruby/thread.h"

#ifdef _WIN32
#include <winsock2.h>
#include <windows.h>
#else
#include <sys/wait.h>
#include <sys/time.h>
#include <dlfcn.h>
#endif
#include <errno.h>
#ifdef HAVE_FCNTL_H
#include <fcntl.h>
#endif
#ifdef HAVE_SYS_PARAM_H
# include <sys/param.h>
#endif
#include "dln.h"

#include "ruby/util.h"
#undef strdup // ruby_strdup may trigger GC

#ifndef MAXPATHLEN
# define MAXPATHLEN 1024
#endif

#ifdef _WIN32
#define dlopen(name,flag) ((void*)LoadLibrary(name))
#define dlerror() strerror(rb_w32_map_errno(GetLastError()))
#define dlsym(handle,name) ((void*)GetProcAddress((handle),(name)))
#define dlclose(handle) (!FreeLibrary(handle))
#define RTLD_NOW  -1

#define waitpid(pid,stat_loc,options) (WaitForSingleObject((HANDLE)(pid), INFINITE), GetExitCodeProcess((HANDLE)(pid), (LPDWORD)(stat_loc)), CloseHandle((HANDLE)pid), (pid))
#define WIFEXITED(S) ((S) != STILL_ACTIVE)
#define WEXITSTATUS(S) (S)
#define WIFSIGNALED(S) (0)
typedef intptr_t pid_t;
#endif

// Atomically set function pointer if possible.
#define MJIT_ATOMIC_SET(var, val) (void)ATOMIC_PTR_EXCHANGE(var, val)

#define MJIT_TMP_PREFIX "_ruby_mjit_"

// The unit structure that holds metadata of ISeq for MJIT.
struct rb_mjit_unit {
    // Unique order number of unit.
    int id;
    // Dlopen handle of the loaded object file.
    void *handle;
    rb_iseq_t *iseq;
#ifndef _MSC_VER
    // This value is always set for `compact_all_jit_code`. Also used for lazy deletion.
    char *o_file;
    // true if it's inherited from parent Ruby process and lazy deletion should be skipped.
    // `o_file = NULL` can't be used to skip lazy deletion because `o_file` could be used
    // by child for `compact_all_jit_code`.
    bool o_file_inherited_p;
#endif
#if defined(_WIN32)
    // DLL cannot be removed while loaded on Windows. If this is set, it'll be lazily deleted.
    char *so_file;
#endif
    // Only used by unload_units. Flag to check this unit is currently on stack or not.
    char used_code_p;
    struct list_node unode;
    // mjit_compile's optimization switches
    struct rb_mjit_compile_info compile_info;
};

// Linked list of struct rb_mjit_unit.
struct rb_mjit_unit_list {
    struct list_head head;
    int length; // the list length
};

extern void rb_native_mutex_lock(rb_nativethread_lock_t *lock);
extern void rb_native_mutex_unlock(rb_nativethread_lock_t *lock);
extern void rb_native_mutex_initialize(rb_nativethread_lock_t *lock);
extern void rb_native_mutex_destroy(rb_nativethread_lock_t *lock);

extern void rb_native_cond_initialize(rb_nativethread_cond_t *cond);
extern void rb_native_cond_destroy(rb_nativethread_cond_t *cond);
extern void rb_native_cond_signal(rb_nativethread_cond_t *cond);
extern void rb_native_cond_broadcast(rb_nativethread_cond_t *cond);
extern void rb_native_cond_wait(rb_nativethread_cond_t *cond, rb_nativethread_lock_t *mutex);

// process.c
extern rb_pid_t ruby_waitpid_locked(rb_vm_t *, rb_pid_t, int *status, int options, rb_nativethread_cond_t *cond);

// A copy of MJIT portion of MRI options since MJIT initialization.  We
// need them as MJIT threads still can work when the most MRI data were
// freed.
struct mjit_options mjit_opts;

// true if MJIT is enabled.
bool mjit_enabled = false;
// true if JIT-ed code should be called. When `ruby_vm_event_enabled_global_flags & ISEQ_TRACE_EVENTS`
// and `mjit_call_p == false`, any JIT-ed code execution is cancelled as soon as possible.
bool mjit_call_p = false;

// Priority queue of iseqs waiting for JIT compilation.
// This variable is a pointer to head unit of the queue.
static struct rb_mjit_unit_list unit_queue = { LIST_HEAD_INIT(unit_queue.head) };
// List of units which are successfully compiled.
static struct rb_mjit_unit_list active_units = { LIST_HEAD_INIT(active_units.head) };
// List of compacted so files which will be cleaned up by `free_list()` in `mjit_finish()`.
static struct rb_mjit_unit_list compact_units = { LIST_HEAD_INIT(compact_units.head) };
// List of units before recompilation and just waiting for dlclose().
static struct rb_mjit_unit_list stale_units = { LIST_HEAD_INIT(stale_units.head) };
// The number of so far processed ISEQs, used to generate unique id.
static int current_unit_num;
// A mutex for conitionals and critical sections.
static rb_nativethread_lock_t mjit_engine_mutex;
// A thread conditional to wake up `mjit_finish` at the end of PCH thread.
static rb_nativethread_cond_t mjit_pch_wakeup;
// A thread conditional to wake up the client if there is a change in
// executed unit status.
static rb_nativethread_cond_t mjit_client_wakeup;
// A thread conditional to wake up a worker if there we have something
// to add or we need to stop MJIT engine.
static rb_nativethread_cond_t mjit_worker_wakeup;
// A thread conditional to wake up workers if at the end of GC.
static rb_nativethread_cond_t mjit_gc_wakeup;
// True when GC is working.
static bool in_gc;
// True when JIT is working.
static bool in_jit;
// Set to true to stop worker.
static bool stop_worker_p;
// Set to true if worker is stopped.
static bool worker_stopped;

// Path of "/tmp", which can be changed to $TMP in MinGW.
static char *tmp_dir;
// Hash like { 1 => true, 2 => true, ... } whose keys are valid `class_serial`s.
// This is used to invalidate obsoleted CALL_CACHE.
static VALUE valid_class_serials;

// Used C compiler path.
static const char *cc_path;
// Used C compiler flags.
static const char **cc_common_args;
// Name of the precompiled header file.
static char *pch_file;
// The process id which should delete the pch_file on mjit_finish.
static rb_pid_t pch_owner_pid;
// Status of the precompiled header creation.  The status is
// shared by the workers and the pch thread.
static enum {PCH_NOT_READY, PCH_FAILED, PCH_SUCCESS} pch_status;

#ifndef _MSC_VER
// Name of the header file.
static char *header_file;
#endif

#ifdef _WIN32
// Linker option to enable libruby.
static char *libruby_pathflag;
#endif

#include "mjit_config.h"

#if defined(__GNUC__) && \
     (!defined(__clang__) || \
      (defined(__clang__) && (defined(__FreeBSD__) || defined(__GLIBC__))))
# define GCC_PIC_FLAGS "-Wfatal-errors", "-fPIC", "-shared", "-w", "-pipe",
# define MJIT_CFLAGS_PIPE 1
#else
# define GCC_PIC_FLAGS /* empty */
# define MJIT_CFLAGS_PIPE 0
#endif

// Use `-nodefaultlibs -nostdlib` for GCC where possible, which does not work on mingw, cygwin, AIX, and OpenBSD.
// This seems to improve MJIT performance on GCC.
#if defined __GNUC__ && !defined __clang__ && !defined(_WIN32) && !defined(__CYGWIN__) && !defined(_AIX) && !defined(__OpenBSD__)
# define GCC_NOSTDLIB_FLAGS "-nodefaultlibs", "-nostdlib",
#else
# define GCC_NOSTDLIB_FLAGS // empty
#endif

static const char *const CC_COMMON_ARGS[] = {
    MJIT_CC_COMMON MJIT_CFLAGS GCC_PIC_FLAGS
    NULL
};

static const char *const CC_DEBUG_ARGS[] = {MJIT_DEBUGFLAGS NULL};
static const char *const CC_OPTIMIZE_ARGS[] = {MJIT_OPTFLAGS NULL};

static const char *const CC_LDSHARED_ARGS[] = {MJIT_LDSHARED GCC_PIC_FLAGS NULL};
static const char *const CC_DLDFLAGS_ARGS[] = {
    MJIT_DLDFLAGS
#if defined __GNUC__ && !defined __clang__ && !defined(__OpenBSD__)
    "-nostartfiles",
#endif
    GCC_NOSTDLIB_FLAGS NULL
};

static const char *const CC_LIBS[] = {
#if defined(_WIN32) || defined(__CYGWIN__)
    MJIT_LIBS // mswin, mingw, cygwin
#endif
#if defined __GNUC__ && !defined __clang__
# if defined(_WIN32)
    "-lmsvcrt", // mingw
# endif
    "-lgcc", // mingw, cygwin, and GCC platforms using `-nodefaultlibs -nostdlib`
#endif
    NULL
};

#define CC_CODEFLAG_ARGS (mjit_opts.debug ? CC_DEBUG_ARGS : CC_OPTIMIZE_ARGS)

// Print the arguments according to FORMAT to stderr only if MJIT
// verbose option value is more or equal to LEVEL.
PRINTF_ARGS(static void, 2, 3)
verbose(int level, const char *format, ...)
{
    if (mjit_opts.verbose >= level) {
        va_list args;
        size_t len = strlen(format);
        char *full_format = alloca(sizeof(char) * (len + 2));

        // Creating `format + '\n'` to atomically print format and '\n'.
        memcpy(full_format, format, len);
        full_format[len] = '\n';
        full_format[len+1] = '\0';

        va_start(args, format);
        vfprintf(stderr, full_format, args);
        va_end(args);
    }
}

PRINTF_ARGS(static void, 1, 2)
mjit_warning(const char *format, ...)
{
    if (mjit_opts.warnings || mjit_opts.verbose) {
        va_list args;

        fprintf(stderr, "MJIT warning: ");
        va_start(args, format);
        vfprintf(stderr, format, args);
        va_end(args);
        fprintf(stderr, "\n");
    }
}

// Add unit node to the tail of doubly linked `list`. It should be not in
// the list before.
static void
add_to_list(struct rb_mjit_unit *unit, struct rb_mjit_unit_list *list)
{
    (void)RB_DEBUG_COUNTER_INC_IF(mjit_length_unit_queue, list == &unit_queue);
    (void)RB_DEBUG_COUNTER_INC_IF(mjit_length_active_units, list == &active_units);
    (void)RB_DEBUG_COUNTER_INC_IF(mjit_length_compact_units, list == &compact_units);
    (void)RB_DEBUG_COUNTER_INC_IF(mjit_length_stale_units, list == &stale_units);

    list_add_tail(&list->head, &unit->unode);
    list->length++;
}

static void
remove_from_list(struct rb_mjit_unit *unit, struct rb_mjit_unit_list *list)
{
#if USE_DEBUG_COUNTER
    rb_debug_counter_add(RB_DEBUG_COUNTER_mjit_length_unit_queue, -1, list == &unit_queue);
    rb_debug_counter_add(RB_DEBUG_COUNTER_mjit_length_active_units, -1, list == &active_units);
    rb_debug_counter_add(RB_DEBUG_COUNTER_mjit_length_compact_units, -1, list == &compact_units);
    rb_debug_counter_add(RB_DEBUG_COUNTER_mjit_length_stale_units, -1, list == &stale_units);
#endif

    list_del(&unit->unode);
    list->length--;
}

static void
remove_file(const char *filename)
{
    if (remove(filename)) {
        mjit_warning("failed to remove \"%s\": %s", filename, strerror(errno));
    }
}

// Lazily delete .o and/or .so files.
static void
clean_object_files(struct rb_mjit_unit *unit)
{
#ifndef _MSC_VER
    if (unit->o_file) {
        char *o_file = unit->o_file;

        unit->o_file = NULL;
        // For compaction, unit->o_file is always set when compilation succeeds.
        // So save_temps needs to be checked here.
        if (!mjit_opts.save_temps && !unit->o_file_inherited_p)
            remove_file(o_file);
        free(o_file);
    }
#endif

#if defined(_WIN32)
    if (unit->so_file) {
        char *so_file = unit->so_file;

        unit->so_file = NULL;
        // unit->so_file is set only when mjit_opts.save_temps is false.
        remove_file(so_file);
        free(so_file);
    }
#endif
}

// This is called in the following situations:
// 1) On dequeue or `unload_units()`, associated ISeq is already GCed.
// 2) The unit is not called often and unloaded by `unload_units()`.
// 3) Freeing lists on `mjit_finish()`.
//
// `jit_func` value does not matter for 1 and 3 since the unit won't be used anymore.
// For the situation 2, this sets the ISeq's JIT state to NOT_COMPILED_JIT_ISEQ_FUNC
// to prevent the situation that the same methods are continuously compiled.
static void
free_unit(struct rb_mjit_unit *unit)
{
    if (unit->iseq) { // ISeq is not GCed
        unit->iseq->body->jit_func = (mjit_func_t)NOT_COMPILED_JIT_ISEQ_FUNC;
        unit->iseq->body->jit_unit = NULL;
    }
    if (unit->handle && dlclose(unit->handle)) { // handle is NULL if it's in queue
        mjit_warning("failed to close handle for u%d: %s", unit->id, dlerror());
    }
    clean_object_files(unit);
    free(unit);
}

// Start a critical section. Use message `msg` to print debug info at `level`.
static inline void
CRITICAL_SECTION_START(int level, const char *msg)
{
    verbose(level, "Locking %s", msg);
    rb_native_mutex_lock(&mjit_engine_mutex);
    verbose(level, "Locked %s", msg);
}

// Finish the current critical section. Use message `msg` to print
// debug info at `level`.
static inline void
CRITICAL_SECTION_FINISH(int level, const char *msg)
{
    verbose(level, "Unlocked %s", msg);
    rb_native_mutex_unlock(&mjit_engine_mutex);
}

static int
sprint_uniq_filename(char *str, size_t size, unsigned long id, const char *prefix, const char *suffix)
{
    return snprintf(str, size, "%s/%sp%"PRI_PIDT_PREFIX"uu%lu%s", tmp_dir, prefix, getpid(), id, suffix);
}

// Return time in milliseconds as a double.
#ifdef __APPLE__
double ruby_real_ms_time(void);
# define real_ms_time() ruby_real_ms_time()
#else
static double
real_ms_time(void)
{
# ifdef HAVE_CLOCK_GETTIME
    struct timespec  tv;
#  ifdef CLOCK_MONOTONIC
    const clockid_t c = CLOCK_MONOTONIC;
#  else
    const clockid_t c = CLOCK_REALTIME;
#  endif

    clock_gettime(c, &tv);
    return tv.tv_nsec / 1000000.0 + tv.tv_sec * 1000.0;
# else
    struct timeval  tv;

    gettimeofday(&tv, NULL);
    return tv.tv_usec / 1000.0 + tv.tv_sec * 1000.0;
# endif
}
#endif

// Return true if class_serial is not obsoleted. This is used by mjit_compile.c.
bool
mjit_valid_class_serial_p(rb_serial_t class_serial)
{
    CRITICAL_SECTION_START(3, "in valid_class_serial_p");
    bool found_p = rb_hash_stlike_lookup(valid_class_serials, LONG2FIX(class_serial), NULL);
    CRITICAL_SECTION_FINISH(3, "in valid_class_serial_p");
    return found_p;
}

// Return the best unit from list.  The best is the first
// high priority unit or the unit whose iseq has the biggest number
// of calls so far.
static struct rb_mjit_unit *
get_from_list(struct rb_mjit_unit_list *list)
{
    struct rb_mjit_unit *unit = NULL, *next, *best = NULL;

    // Find iseq with max total_calls
    list_for_each_safe(&list->head, unit, next, unode) {
        if (unit->iseq == NULL) { // ISeq is GCed.
            remove_from_list(unit, list);
            free_unit(unit);
            continue;
        }

        if (best == NULL || best->iseq->body->total_calls < unit->iseq->body->total_calls) {
            best = unit;
        }
    }
    if (best) {
        remove_from_list(best, list);
    }
    return best;
}

// Return length of NULL-terminated array `args` excluding the NULL marker.
static size_t
args_len(char *const *args)
{
    size_t i;

    for (i = 0; (args[i]) != NULL;i++)
        ;
    return i;
}

// Concatenate `num` passed NULL-terminated arrays of strings, put the
// result (with NULL end marker) into the heap, and return the result.
static char **
form_args(int num, ...)
{
    va_list argp;
    size_t len, n;
    int i;
    char **args, **res, **tmp;

    va_start(argp, num);
    res = NULL;
    for (i = len = 0; i < num; i++) {
        args = va_arg(argp, char **);
        n = args_len(args);
        if ((tmp = (char **)realloc(res, sizeof(char *) * (len + n + 1))) == NULL) {
            free(res);
            return NULL;
        }
        res = tmp;
        MEMCPY(res + len, args, char *, n + 1);
        len += n;
    }
    va_end(argp);
    return res;
}

COMPILER_WARNING_PUSH
#ifdef __GNUC__
COMPILER_WARNING_IGNORED(-Wdeprecated-declarations)
#endif
// Start an OS process of absolute executable path with arguments `argv`.
// Return PID of the process.
static pid_t
start_process(const char *abspath, char *const *argv)
{
    pid_t pid;
    // Not calling non-async-signal-safe functions between vfork
    // and execv for safety
    int dev_null = rb_cloexec_open(ruby_null_device, O_WRONLY, 0);

    if (mjit_opts.verbose >= 2) {
        int i;
        const char *arg;

        fprintf(stderr, "Starting process: %s", abspath);
        for (i = 0; (arg = argv[i]) != NULL; i++)
            fprintf(stderr, " %s", arg);
        fprintf(stderr, "\n");
    }
#ifdef _WIN32
    {
        extern HANDLE rb_w32_start_process(const char *abspath, char *const *argv, int out_fd);
        int out_fd = 0;
        if (mjit_opts.verbose <= 1) {
            // Discard cl.exe's outputs like:
            //   _ruby_mjit_p12u3.c
            //     Creating library C:.../_ruby_mjit_p12u3.lib and object C:.../_ruby_mjit_p12u3.exp
            out_fd = dev_null;
        }

        pid = (pid_t)rb_w32_start_process(abspath, argv, out_fd);
        if (pid == 0) {
            verbose(1, "MJIT: Failed to create process: %s", dlerror());
            return -1;
        }
    }
#else
    if ((pid = vfork()) == 0) { /* TODO: reuse some function in process.c */
        umask(0077);
        if (mjit_opts.verbose == 0) {
            // CC can be started in a thread using a file which has been
            // already removed while MJIT is finishing.  Discard the
            // messages about missing files.
            dup2(dev_null, STDERR_FILENO);
            dup2(dev_null, STDOUT_FILENO);
        }
        (void)close(dev_null);
        pid = execv(abspath, argv); // Pid will be negative on an error
        // Even if we successfully found CC to compile PCH we still can
        // fail with loading the CC in very rare cases for some reasons.
        // Stop the forked process in this case.
        verbose(1, "MJIT: Error in execv: %s", abspath);
        _exit(1);
    }
#endif
    (void)close(dev_null);
    return pid;
}
COMPILER_WARNING_POP

// Execute an OS process of executable PATH with arguments ARGV.
// Return -1 or -2 if failed to execute, otherwise exit code of the process.
// TODO: Use a similar function in process.c
static int
exec_process(const char *path, char *const argv[])
{
    int stat, exit_code = -2;
    pid_t pid;
    rb_vm_t *vm = WAITPID_USE_SIGCHLD ? GET_VM() : 0;
    rb_nativethread_cond_t cond;

    if (vm) {
        rb_native_cond_initialize(&cond);
        rb_native_mutex_lock(&vm->waitpid_lock);
    }

    pid = start_process(path, argv);
    for (;pid > 0;) {
        pid_t r = vm ? ruby_waitpid_locked(vm, pid, &stat, 0, &cond)
                     : waitpid(pid, &stat, 0);
        if (r == -1) {
            if (errno == EINTR) continue;
            fprintf(stderr, "[%"PRI_PIDT_PREFIX"d] waitpid(%lu): %s (SIGCHLD=%d,%u)\n",
                    getpid(), (unsigned long)pid, strerror(errno),
                    RUBY_SIGCHLD, SIGCHLD_LOSSY);
            break;
        }
        else if (r == pid) {
            if (WIFEXITED(stat)) {
                exit_code = WEXITSTATUS(stat);
                break;
            }
            else if (WIFSIGNALED(stat)) {
                exit_code = -1;
                break;
            }
        }
    }

    if (vm) {
        rb_native_mutex_unlock(&vm->waitpid_lock);
        rb_native_cond_destroy(&cond);
    }
    return exit_code;
}

static void
remove_so_file(const char *so_file, struct rb_mjit_unit *unit)
{
#if defined(_WIN32)
    // Windows can't remove files while it's used.
    unit->so_file = strdup(so_file); // lazily delete on `clean_object_files()`
    if (unit->so_file == NULL)
        mjit_warning("failed to allocate memory to lazily remove '%s': %s", so_file, strerror(errno));
#else
    remove_file(so_file);
#endif
}

#define append_str2(p, str, len) ((char *)memcpy((p), str, (len))+(len))
#define append_str(p, str) append_str2(p, str, sizeof(str)-1)
#define append_lit(p, str) append_str2(p, str, rb_strlen_lit(str))

#ifdef _MSC_VER
// Compile C file to so. It returns true if it succeeds. (mswin)
static bool
compile_c_to_so(const char *c_file, const char *so_file)
{
    int exit_code;
    const char *files[] = { NULL, NULL, NULL, NULL, NULL, NULL, "-link", libruby_pathflag, NULL };
    char **args;
    char *p, *obj_file;

    // files[0] = "-Fe*.dll"
    files[0] = p = alloca(sizeof(char) * (rb_strlen_lit("-Fe") + strlen(so_file) + 1));
    p = append_lit(p, "-Fe");
    p = append_str2(p, so_file, strlen(so_file));
    *p = '\0';

    // files[1] = "-Fo*.obj"
    // We don't need .obj file, but it's somehow created to cwd without -Fo and we want to control the output directory.
    files[1] = p = alloca(sizeof(char) * (rb_strlen_lit("-Fo") + strlen(so_file) - rb_strlen_lit(DLEXT) + rb_strlen_lit(".obj") + 1));
    obj_file = p = append_lit(p, "-Fo");
    p = append_str2(p, so_file, strlen(so_file) - rb_strlen_lit(DLEXT));
    p = append_lit(p, ".obj");
    *p = '\0';

    // files[2] = "-Yu*.pch"
    files[2] = p = alloca(sizeof(char) * (rb_strlen_lit("-Yu") + strlen(pch_file) + 1));
    p = append_lit(p, "-Yu");
    p = append_str2(p, pch_file, strlen(pch_file));
    *p = '\0';

    // files[3] = "C:/.../rb_mjit_header-*.obj"
    files[3] = p = alloca(sizeof(char) * (strlen(pch_file) + 1));
    p = append_str2(p, pch_file, strlen(pch_file) - strlen(".pch"));
    p = append_lit(p, ".obj");
    *p = '\0';

    // files[4] = "-Tc*.c"
    files[4] = p = alloca(sizeof(char) * (rb_strlen_lit("-Tc") + strlen(c_file) + 1));
    p = append_lit(p, "-Tc");
    p = append_str2(p, c_file, strlen(c_file));
    *p = '\0';

    // files[5] = "-Fd*.pdb"
    files[5] = p = alloca(sizeof(char) * (rb_strlen_lit("-Fd") + strlen(pch_file) + 1));
    p = append_lit(p, "-Fd");
    p = append_str2(p, pch_file, strlen(pch_file) - rb_strlen_lit(".pch"));
    p = append_lit(p, ".pdb");
    *p = '\0';

    args = form_args(5, CC_LDSHARED_ARGS, CC_CODEFLAG_ARGS,
                     files, CC_LIBS, CC_DLDFLAGS_ARGS);
    if (args == NULL)
        return false;

    exit_code = exec_process(cc_path, args);
    free(args);

    if (exit_code == 0) {
        // remove never-used files (.obj, .lib, .exp, .pdb). XXX: Is there any way not to generate this?
        if (!mjit_opts.save_temps) {
            char *before_dot;
            remove_file(obj_file);

            before_dot = obj_file + strlen(obj_file) - rb_strlen_lit(".obj");
            append_lit(before_dot, ".lib"); remove_file(obj_file);
            append_lit(before_dot, ".exp"); remove_file(obj_file);
            append_lit(before_dot, ".pdb"); remove_file(obj_file);
        }
    }
    else {
        verbose(2, "compile_c_to_so: compile error: %d", exit_code);
    }
    return exit_code == 0;
}
#else // _MSC_VER

// The function producing the pre-compiled header.
static void
make_pch(void)
{
    int exit_code;
    const char *rest_args[] = {
# ifdef __clang__
        "-emit-pch",
# endif
        // -nodefaultlibs is a linker flag, but it may affect cc1 behavior on Gentoo, which should NOT be changed on pch:
        // https://gitweb.gentoo.org/proj/gcc-patches.git/tree/7.3.0/gentoo/13_all_default-ssp-fix.patch
        GCC_NOSTDLIB_FLAGS
        "-o", NULL, NULL,
        NULL,
    };
    char **args;
    int len = sizeof(rest_args) / sizeof(const char *);

    rest_args[len - 2] = header_file;
    rest_args[len - 3] = pch_file;
    verbose(2, "Creating precompiled header");
    args = form_args(3, cc_common_args, CC_CODEFLAG_ARGS, rest_args);
    if (args == NULL) {
        mjit_warning("making precompiled header failed on forming args");
        CRITICAL_SECTION_START(3, "in make_pch");
        pch_status = PCH_FAILED;
        CRITICAL_SECTION_FINISH(3, "in make_pch");
        return;
    }

    exit_code = exec_process(cc_path, args);
    free(args);

    CRITICAL_SECTION_START(3, "in make_pch");
    if (exit_code == 0) {
        pch_status = PCH_SUCCESS;
    }
    else {
        mjit_warning("Making precompiled header failed on compilation. Stopping MJIT worker...");
        pch_status = PCH_FAILED;
    }
    /* wakeup `mjit_finish` */
    rb_native_cond_broadcast(&mjit_pch_wakeup);
    CRITICAL_SECTION_FINISH(3, "in make_pch");
}

// Compile .c file to .o file. It returns true if it succeeds. (non-mswin)
static bool
compile_c_to_o(const char *c_file, const char *o_file)
{
    int exit_code;
    const char *files[] = {
        "-o", NULL, NULL,
# ifdef __clang__
        "-include-pch", NULL,
# endif
        "-c", NULL
    };
    char **args;

    files[1] = o_file;
    files[2] = c_file;
# ifdef __clang__
    files[4] = pch_file;
# endif
    args = form_args(5, cc_common_args, CC_CODEFLAG_ARGS, files, CC_LIBS, CC_DLDFLAGS_ARGS);
    if (args == NULL)
        return false;

    exit_code = exec_process(cc_path, args);
    free(args);

    if (exit_code != 0)
        verbose(2, "compile_c_to_o: compile error: %d", exit_code);
    return exit_code == 0;
}

// Link .o files to .so file. It returns true if it succeeds. (non-mswin)
static bool
link_o_to_so(const char **o_files, const char *so_file)
{
    int exit_code;
    const char *options[] = {
        "-o", NULL,
# ifdef _WIN32
        libruby_pathflag,
# endif
        NULL
    };
    char **args;

    options[1] = so_file;
    args = form_args(6, CC_LDSHARED_ARGS, CC_CODEFLAG_ARGS,
                     options, o_files, CC_LIBS, CC_DLDFLAGS_ARGS);
    if (args == NULL)
        return false;

    exit_code = exec_process(cc_path, args);
    free(args);

    if (exit_code != 0)
        verbose(2, "link_o_to_so: link error: %d", exit_code);
    return exit_code == 0;
}

// Link all cached .o files and build a .so file. Reload all JIT func from it. This
// allows to avoid JIT code fragmentation and improve performance to call JIT-ed code.
static void
compact_all_jit_code(void)
{
# ifndef _WIN32 // This requires header transformation but we don't transform header on Windows for now
    struct rb_mjit_unit *unit, *cur = 0;
    double start_time, end_time;
    static const char so_ext[] = DLEXT;
    char so_file[MAXPATHLEN];
    const char **o_files;
    int i = 0;

    // Abnormal use case of rb_mjit_unit that doesn't have ISeq
    unit = calloc(1, sizeof(struct rb_mjit_unit)); // To prevent GC, don't use ZALLOC
    if (unit == NULL) return;
    unit->id = current_unit_num++;
    sprint_uniq_filename(so_file, (int)sizeof(so_file), unit->id, MJIT_TMP_PREFIX, so_ext);

    // NULL-ending for form_args
    o_files = alloca(sizeof(char *) * (active_units.length + 1));
    o_files[active_units.length] = NULL;
    CRITICAL_SECTION_START(3, "in compact_all_jit_code to keep .o files");
    list_for_each(&active_units.head, cur, unode) {
        o_files[i] = cur->o_file;
        i++;
    }

    start_time = real_ms_time();
    bool success = link_o_to_so(o_files, so_file);
    end_time = real_ms_time();

    // TODO: Shrink this big critical section. For now, this is needed to prevent failure by missing .o files.
    // This assumes that o -> so link doesn't take long time because the bottleneck, which is compiler optimization,
    // is already done. But actually it takes about 500ms for 5,000 methods on my Linux machine, so it's better to
    // finish this critical section before link_o_to_so by disabling unload_units.
    CRITICAL_SECTION_FINISH(3, "in compact_all_jit_code to keep .o files");

    if (success) {
        void *handle = dlopen(so_file, RTLD_NOW);
        if (handle == NULL) {
            mjit_warning("failure in loading code from compacted '%s': %s", so_file, dlerror());
            free(unit);
            return;
        }
        unit->handle = handle;

        // lazily dlclose handle (and .so file for win32) on `mjit_finish()`.
        add_to_list(unit, &compact_units);

        if (!mjit_opts.save_temps)
            remove_so_file(so_file, unit);

        CRITICAL_SECTION_START(3, "in compact_all_jit_code to read list");
        list_for_each(&active_units.head, cur, unode) {
            void *func;
            char funcname[35]; // TODO: reconsider `35`
            sprintf(funcname, "_mjit%d", cur->id);

            if ((func = dlsym(handle, funcname)) == NULL) {
                mjit_warning("skipping to reload '%s' from '%s': %s", funcname, so_file, dlerror());
                continue;
            }

            if (cur->iseq) { // Check whether GCed or not
                // Usage of jit_code might be not in a critical section.
                MJIT_ATOMIC_SET(cur->iseq->body->jit_func, (mjit_func_t)func);
            }
        }
        CRITICAL_SECTION_FINISH(3, "in compact_all_jit_code to read list");
        verbose(1, "JIT compaction (%.1fms): Compacted %d methods -> %s", end_time - start_time, active_units.length, so_file);
    }
    else {
        free(unit);
        verbose(1, "JIT compaction failure (%.1fms): Failed to compact methods", end_time - start_time);
    }
# endif // _WIN32
}

#endif // _MSC_VER

static void *
load_func_from_so(const char *so_file, const char *funcname, struct rb_mjit_unit *unit)
{
    void *handle, *func;

    handle = dlopen(so_file, RTLD_NOW);
    if (handle == NULL) {
        mjit_warning("failure in loading code from '%s': %s", so_file, dlerror());
        return (void *)NOT_ADDED_JIT_ISEQ_FUNC;
    }

    func = dlsym(handle, funcname);
    unit->handle = handle;
    return func;
}

static void
print_jit_result(const char *result, const struct rb_mjit_unit *unit, const double duration, const char *c_file)
{
    if (unit->iseq == NULL) {
        verbose(1, "JIT %s (%.1fms): (GCed) -> %s", result, duration, c_file);
    }
    else {
        verbose(1, "JIT %s (%.1fms): %s@%s:%d -> %s", result,
                duration, RSTRING_PTR(unit->iseq->body->location.label),
                RSTRING_PTR(rb_iseq_path(unit->iseq)), FIX2INT(unit->iseq->body->location.first_lineno), c_file);
    }
}

#ifndef __clang__
static const char *
header_name_end(const char *s)
{
    const char *e = s + strlen(s);
# ifdef __GNUC__ // don't chomp .pch for mswin
    static const char suffix[] = ".gch";

    // chomp .gch suffix
    if (e > s+sizeof(suffix)-1 && strcmp(e-sizeof(suffix)+1, suffix) == 0) {
        e -= sizeof(suffix)-1;
    }
# endif
    return e;
}
#endif

// Print platform-specific prerequisites in generated code.
static void
compile_prelude(FILE *f)
{
#ifndef __clang__ // -include-pch is used for Clang
    const char *s = pch_file;
    const char *e = header_name_end(s);

    fprintf(f, "#include \"");
    // print pch_file except .gch for gcc, but keep .pch for mswin
    for (; s < e; s++) {
        switch(*s) {
          case '\\': case '"':
            fputc('\\', f);
        }
        fputc(*s, f);
    }
    fprintf(f, "\"\n");
#endif

#ifdef _WIN32
    fprintf(f, "void _pei386_runtime_relocator(void){}\n");
    fprintf(f, "int __stdcall DllMainCRTStartup(void* hinstDLL, unsigned int fdwReason, void* lpvReserved) { return 1; }\n");
#endif
}

// Compile ISeq in UNIT and return function pointer of JIT-ed code.
// It may return NOT_COMPILED_JIT_ISEQ_FUNC if something went wrong.
static mjit_func_t
convert_unit_to_func(struct rb_mjit_unit *unit)
{
    char c_file_buff[MAXPATHLEN], *c_file = c_file_buff, *so_file, funcname[35]; // TODO: reconsider `35`
    int fd;
    FILE *f;
    void *func;
    double start_time, end_time;
    int c_file_len = (int)sizeof(c_file_buff);
    static const char c_ext[] = ".c";
    static const char so_ext[] = DLEXT;
    const int access_mode =
#ifdef O_BINARY
        O_BINARY|
#endif
        O_WRONLY|O_EXCL|O_CREAT;
#ifndef _MSC_VER
    static const char o_ext[] = ".o";
    char *o_file;
#endif

    c_file_len = sprint_uniq_filename(c_file_buff, c_file_len, unit->id, MJIT_TMP_PREFIX, c_ext);
    if (c_file_len >= (int)sizeof(c_file_buff)) {
        ++c_file_len;
        c_file = alloca(c_file_len);
        c_file_len = sprint_uniq_filename(c_file, c_file_len, unit->id, MJIT_TMP_PREFIX, c_ext);
    }
    ++c_file_len;

#ifndef _MSC_VER
    o_file = alloca(c_file_len - sizeof(c_ext) + sizeof(o_ext));
    memcpy(o_file, c_file, c_file_len - sizeof(c_ext));
    memcpy(&o_file[c_file_len - sizeof(c_ext)], o_ext, sizeof(o_ext));
#endif
    so_file = alloca(c_file_len - sizeof(c_ext) + sizeof(so_ext));
    memcpy(so_file, c_file, c_file_len - sizeof(c_ext));
    memcpy(&so_file[c_file_len - sizeof(c_ext)], so_ext, sizeof(so_ext));

    sprintf(funcname, "_mjit%d", unit->id);

    fd = rb_cloexec_open(c_file, access_mode, 0600);
    if (fd < 0 || (f = fdopen(fd, "w")) == NULL) {
        int e = errno;
        if (fd >= 0) (void)close(fd);
        verbose(1, "Failed to fopen '%s', giving up JIT for it (%s)", c_file, strerror(e));
        return (mjit_func_t)NOT_COMPILED_JIT_ISEQ_FUNC;
    }

    // print #include of MJIT header, etc.
    compile_prelude(f);

    // wait until mjit_gc_exit_hook is called
    CRITICAL_SECTION_START(3, "before mjit_compile to wait GC finish");
    while (in_gc) {
        verbose(3, "Waiting wakeup from GC");
        rb_native_cond_wait(&mjit_gc_wakeup, &mjit_engine_mutex);
    }

    // We need to check again here because we could've waited on GC above
    if (unit->iseq == NULL) {
        fclose(f);
        if (!mjit_opts.save_temps)
            remove_file(c_file);
        free_unit(unit);
        in_jit = false; // just being explicit for return
    }
    else {
        in_jit = true;
    }
    CRITICAL_SECTION_FINISH(3, "before mjit_compile to wait GC finish");
    if (!in_jit) {
        return (mjit_func_t)NOT_COMPILED_JIT_ISEQ_FUNC;
    }

    {
        VALUE s = rb_iseq_path(unit->iseq);
        const char *label = RSTRING_PTR(unit->iseq->body->location.label);
        const char *path = RSTRING_PTR(s);
        int lineno = FIX2INT(unit->iseq->body->location.first_lineno);
        verbose(2, "start compilation: %s@%s:%d -> %s", label, path, lineno, c_file);
        fprintf(f, "/* %s@%s:%d */\n\n", label, path, lineno);
    }
    bool success = mjit_compile(f, unit->iseq, funcname);

    // release blocking mjit_gc_start_hook
    CRITICAL_SECTION_START(3, "after mjit_compile to wakeup client for GC");
    in_jit = false;
    verbose(3, "Sending wakeup signal to client in a mjit-worker for GC");
    rb_native_cond_signal(&mjit_client_wakeup);
    CRITICAL_SECTION_FINISH(3, "in worker to wakeup client for GC");

    fclose(f);
    if (!success) {
        if (!mjit_opts.save_temps)
            remove_file(c_file);
        print_jit_result("failure", unit, 0, c_file);
        return (mjit_func_t)NOT_COMPILED_JIT_ISEQ_FUNC;
    }

    start_time = real_ms_time();
#ifdef _MSC_VER
    success = compile_c_to_so(c_file, so_file);
#else
    // splitting .c -> .o step and .o -> .so step, to cache .o files in the future
    if ((success = compile_c_to_o(c_file, o_file)) != false) {
        const char *o_files[2] = { NULL, NULL };
        o_files[0] = o_file;
        success = link_o_to_so(o_files, so_file);

        // Always set o_file for compaction. The value is also used for lazy deletion.
        unit->o_file = strdup(o_file);
        if (unit->o_file == NULL) {
            mjit_warning("failed to allocate memory to remember '%s' (%s), removing it...", o_file, strerror(errno));
            remove_file(o_file);
        }
    }
#endif
    end_time = real_ms_time();

    if (!mjit_opts.save_temps)
        remove_file(c_file);
    if (!success) {
        verbose(2, "Failed to generate so: %s", so_file);
        return (mjit_func_t)NOT_COMPILED_JIT_ISEQ_FUNC;
    }

    func = load_func_from_so(so_file, funcname, unit);
    if (!mjit_opts.save_temps)
        remove_so_file(so_file, unit);

    if ((uintptr_t)func > (uintptr_t)LAST_JIT_ISEQ_FUNC) {
        CRITICAL_SECTION_START(3, "end of jit");
        add_to_list(unit, &active_units);
        if (unit->iseq)
            print_jit_result("success", unit, end_time - start_time, c_file);
        CRITICAL_SECTION_FINISH(3, "end of jit");
    }
    return (mjit_func_t)func;
}

typedef struct {
    const rb_iseq_t *iseq;
    struct rb_call_cache *cc_entries;
    union iseq_inline_storage_entry *is_entries;
    bool finish_p;
} mjit_copy_job_t;

// Singleton MJIT copy job. This is made global since it needs to be durable even when MJIT worker thread is stopped.
// (ex: register job -> MJIT pause -> MJIT resume -> dispatch job. Actually this should be just cancelled by finish_p check)
static mjit_copy_job_t mjit_copy_job = { .iseq = NULL, .finish_p = true };

static void mjit_copy_job_handler(void *data);

// vm_trace.c
int rb_workqueue_register(unsigned flags, rb_postponed_job_func_t , void *);

// Copy inline cache values of `iseq` to `cc_entries` and `is_entries`.
// These buffers should be pre-allocated properly prior to calling this function.
// Return true if copy succeeds or is not needed.
//
// We're lazily copying cache values from main thread because these cache values
// could be different between ones on enqueue timing and ones on dequeue timing.
bool
mjit_copy_cache_from_main_thread(const rb_iseq_t *iseq, struct rb_call_cache *cc_entries, union iseq_inline_storage_entry *is_entries)
{
    mjit_copy_job_t *job = &mjit_copy_job; // just a short hand

    CRITICAL_SECTION_START(3, "in mjit_copy_cache_from_main_thread");
    job->finish_p = true; // disable dispatching this job in mjit_copy_job_handler while it's being modified
    CRITICAL_SECTION_FINISH(3, "in mjit_copy_cache_from_main_thread");

    job->cc_entries = cc_entries;
    job->is_entries = is_entries;

    CRITICAL_SECTION_START(3, "in mjit_copy_cache_from_main_thread");
    job->iseq = iseq; // Prevernt GC of this ISeq from here
    VM_ASSERT(in_jit);
    in_jit = false; // To avoid deadlock, allow running GC while waiting for copy job
    rb_native_cond_signal(&mjit_client_wakeup); // Unblock main thread waiting in `mjit_gc_start_hook`

    job->finish_p = false; // allow dispatching this job in mjit_copy_job_handler
    CRITICAL_SECTION_FINISH(3, "in mjit_copy_cache_from_main_thread");

    if (UNLIKELY(mjit_opts.wait)) {
        mjit_copy_job_handler((void *)job);
    }
    else if (rb_workqueue_register(0, mjit_copy_job_handler, (void *)job)) {
        CRITICAL_SECTION_START(3, "in MJIT copy job wait");
        // checking `stop_worker_p` too because `RUBY_VM_CHECK_INTS(ec)` may not
        // lush mjit_copy_job_handler when EC_EXEC_TAG() is not TAG_NONE, and then
        // `stop_worker()` could dead lock with this function.
        while (!job->finish_p && !stop_worker_p) {
            rb_native_cond_wait(&mjit_worker_wakeup, &mjit_engine_mutex);
            verbose(3, "Getting wakeup from client");
        }
        CRITICAL_SECTION_FINISH(3, "in MJIT copy job wait");
    }

    CRITICAL_SECTION_START(3, "in mjit_copy_cache_from_main_thread");
    bool success_p = job->finish_p;
    // Disable dispatching this job in mjit_copy_job_handler while memory allocated by alloca
    // could be expired after finishing this function.
    job->finish_p = true;

    in_jit = true; // Prohibit GC during JIT compilation
    if (job->iseq == NULL) // ISeq GC is notified in mjit_mark_iseq
        success_p = false;
    job->iseq = NULL; // Allow future GC of this ISeq from here
    CRITICAL_SECTION_FINISH(3, "in mjit_copy_cache_from_main_thread");
    return success_p;
}

// The function implementing a worker. It is executed in a separate
// thread by rb_thread_create_mjit_thread. It compiles precompiled header
// and then compiles requested ISeqs.
void
mjit_worker(void)
{
#ifndef _MSC_VER
    if (pch_status == PCH_NOT_READY) {
        make_pch();
    }
#endif
    if (pch_status == PCH_FAILED) {
        mjit_enabled = false;
        CRITICAL_SECTION_START(3, "in worker to update worker_stopped");
        worker_stopped = true;
        verbose(3, "Sending wakeup signal to client in a mjit-worker");
        rb_native_cond_signal(&mjit_client_wakeup);
        CRITICAL_SECTION_FINISH(3, "in worker to update worker_stopped");
        return; // TODO: do the same thing in the latter half of mjit_finish
    }

    // main worker loop
    while (!stop_worker_p) {
        struct rb_mjit_unit *unit;

        // wait until unit is available
        CRITICAL_SECTION_START(3, "in worker dequeue");
        while ((list_empty(&unit_queue.head) || active_units.length >= mjit_opts.max_cache_size) && !stop_worker_p) {
            rb_native_cond_wait(&mjit_worker_wakeup, &mjit_engine_mutex);
            verbose(3, "Getting wakeup from client");
        }
        unit = get_from_list(&unit_queue);
        CRITICAL_SECTION_FINISH(3, "in worker dequeue");

        if (unit) {
            // JIT compile
            mjit_func_t func = convert_unit_to_func(unit);
            (void)RB_DEBUG_COUNTER_INC_IF(mjit_compile_failures, func == (mjit_func_t)NOT_COMPILED_JIT_ISEQ_FUNC);

            // `mjit_copy_cache_from_main_thread` in `mjit_compile` may wait for a long time
            // and worker may be stopped during the compilation.
            if (stop_worker_p)
                break;

            CRITICAL_SECTION_START(3, "in jit func replace");
            while (in_gc) { // Make sure we're not GC-ing when touching ISeq
                verbose(3, "Waiting wakeup from GC");
                rb_native_cond_wait(&mjit_gc_wakeup, &mjit_engine_mutex);
            }
            if (unit->iseq) { // Check whether GCed or not
                // Usage of jit_code might be not in a critical section.
                MJIT_ATOMIC_SET(unit->iseq->body->jit_func, func);
            }
            CRITICAL_SECTION_FINISH(3, "in jit func replace");

#ifndef _MSC_VER
            // Combine .o files to one .so and reload all jit_func to improve memory locality
            if ((!mjit_opts.wait && unit_queue.length == 0 && active_units.length > 1)
                || active_units.length == mjit_opts.max_cache_size) {
                compact_all_jit_code();
            }
#endif
        }
    }

    // To keep mutex unlocked when it is destroyed by mjit_finish, don't wrap CRITICAL_SECTION here.
    worker_stopped = true;
}