mjit_worker.c: carve out worker-related code

The motivation of this change is to make sure rb_funcall or GC-related
functions are not called on worker-related code. Currently such
functions are used in some places and I believe it's partly because it's
hard to identify which part is called on MJIT worker thread.

Now, mjit.c is safe to use them but we know we need to safely deal with
mjit_compile.c, mjit_worker.c and mjit_internal.h.

mjit_compile.c: update the comment about it

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64285 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 896 insertions, 0 deletions

diff --git a/mjit_worker.c b/mjit_worker.c
new file mode 100644
index 0000000000..57c30165b4
--- /dev/null
+++ b/mjit_worker.c
@@ -0,0 +1,896 @@
+/**********************************************************************
+
+  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 xmalloc, ZALLOC, 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 "internal.h"
+#include "vm_core.h"
+#include "mjit.h"
+#include "gc.h"
+#include "constant.h"
+#include "id_table.h"
+#include "ruby_assert.h"
+#include "ruby/thread.h"
+#include "ruby/util.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 "mjit_internal.h"
+
+/* process.c */
+rb_pid_t ruby_waitpid_locked(rb_vm_t *, rb_pid_t, int *status, int options,
+                          rb_nativethread_cond_t *cond);
+
+/* Atomically set function pointer if possible. */
+#define MJIT_ATOMIC_SET(var, val) (void)ATOMIC_PTR_EXCHANGE(var, val)
+
+extern struct mjit_options mjit_opts;
+extern int mjit_enabled;
+
+extern struct rb_mjit_unit_list mjit_unit_queue;
+extern struct rb_mjit_unit_list mjit_active_units;
+extern struct rb_mjit_unit_list mjit_compact_units;
+extern int mjit_current_unit_num;
+extern rb_nativethread_cond_t mjit_pch_wakeup;
+extern rb_nativethread_cond_t mjit_client_wakeup;
+extern rb_nativethread_cond_t mjit_worker_wakeup;
+extern rb_nativethread_cond_t mjit_gc_wakeup;
+
+extern int mjit_in_gc;
+extern int mjit_in_jit;
+
+/* --- Defined in the client thread before starting MJIT threads: ---  */
+/* Used C compiler path.  */
+const char *mjit_cc_path;
+/* Name of the precompiled header file.  */
+char *mjit_pch_file;
+
+#ifndef _MSC_VER
+/* Name of the header file.  */
+char *mjit_header_file;
+#endif
+
+#ifdef _WIN32
+/* Linker option to enable libruby. */
+char *mjit_libruby_pathflag;
+#endif
+
+/* 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
+
+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__
+    "-nostartfiles",
+# if !defined(_WIN32) && !defined(__CYGWIN__)
+    "-nodefaultlibs", "-nostdlib",
+# endif
+#endif
+    NULL
+};
+
+static const char *const CC_LIBS[] = {
+#if defined(_WIN32) || defined(__CYGWIN__)
+    MJIT_LIBS
+# if defined __GNUC__ && !defined __clang__
+#  if defined(_WIN32)
+    "-lmsvcrt",
+#  endif
+    "-lgcc",
+# endif
+#endif
+    NULL
+};
+
+#define CC_CODEFLAG_ARGS (mjit_opts.debug ? CC_DEBUG_ARGS : CC_OPTIMIZE_ARGS)
+
+/* Status of the precompiled header creation.  The status is
+   shared by the workers and the pch thread.  */
+enum pch_status_t pch_status;
+
+/* 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_node *
+get_from_list(struct rb_mjit_unit_list *list)
+{
+    struct rb_mjit_unit_node *node, *best = NULL;
+
+    if (list->head == NULL)
+        return NULL;
+
+    /* Find iseq with max total_calls */
+    for (node = list->head; node != NULL; node = node ? node->next : NULL) {
+        if (node->unit->iseq == NULL) { /* ISeq is GCed. */
+            free_unit(node->unit);
+            remove_from_list(node, list);
+            continue;
+        }
+
+        if (best == NULL || best->unit->iseq->body->total_calls < node->unit->iseq->body->total_calls) {
+            best = node;
+        }
+    }
+
+    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 executable PATH with arguments ARGV.  Return
+   PID of the process.
+   TODO: Use the same function in process.c */
+static pid_t
+start_process(const char *path, char *const *argv)
+{
+    pid_t pid;
+
+    if (mjit_opts.verbose >= 2) {
+        int i;
+        const char *arg;
+
+        fprintf(stderr, "Starting process: %s", path);
+        for (i = 0; (arg = argv[i]) != NULL; i++)
+            fprintf(stderr, " %s", arg);
+        fprintf(stderr, "\n");
+    }
+#ifdef _WIN32
+    pid = spawnvp(_P_NOWAIT, path, argv);
+#else
+    {
+        /*
+         * Not calling non-async-signal-safe functions between vfork
+         * and execv for safety
+         */
+        char fbuf[MAXPATHLEN];
+        const char *abspath = dln_find_exe_r(path, 0, fbuf, sizeof(fbuf));
+        int dev_null;
+
+        if (!abspath) {
+            verbose(1, "MJIT: failed to find `%s' in PATH\n", path);
+            return -1;
+        }
+        dev_null = rb_cloexec_open(ruby_null_device, O_WRONLY, 0);
+
+        if ((pid = vfork()) == 0) {
+            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\n", abspath);
+            _exit(1);
+        }
+        (void)close(dev_null);
+    }
+#endif
+    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;
+}
+
+#ifdef _MSC_VER
+/* Compile C file to so. It returns 1 if it succeeds. (mswin) */
+static int
+compile_c_to_so(const char *c_file, const char *so_file)
+{
+    int exit_code;
+    const char *files[] = { NULL, NULL, NULL, NULL, "-link", mjit_libruby_pathflag, NULL };
+    char **args;
+    char *p;
+
+    /* files[0] = "-Fe*.dll" */
+    files[0] = p = (char *)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] = "-Yu*.pch" */
+    files[1] = p = (char *)alloca(sizeof(char) * (rb_strlen_lit("-Yu") + strlen(mjit_pch_file) + 1));
+    p = append_lit(p, "-Yu");
+    p = append_str2(p, mjit_pch_file, strlen(mjit_pch_file));
+    *p = '\0';
+
+    /* files[2] = "C:/.../rb_mjit_header-*.obj" */
+    files[2] = p = (char *)alloca(sizeof(char) * (strlen(mjit_pch_file) + 1));
+    p = append_str2(p, mjit_pch_file, strlen(mjit_pch_file) - strlen(".pch"));
+    p = append_lit(p, ".obj");
+    *p = '\0';
+
+    /* files[3] = "-Tc*.c" */
+    files[3] = p = (char *)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';
+
+    args = form_args(5, CC_LDSHARED_ARGS, CC_CODEFLAG_ARGS,
+                     files, CC_LIBS, CC_DLDFLAGS_ARGS);
+    if (args == NULL)
+        return FALSE;
+
+    {
+        int stdout_fileno = _fileno(stdout);
+        int orig_fd = dup(stdout_fileno);
+        int dev_null = rb_cloexec_open(ruby_null_device, O_WRONLY, 0);
+
+        /* Discard cl.exe's outputs like:
+             _ruby_mjit_p12u3.c
+               Creating library C:.../_ruby_mjit_p12u3.lib and object C:.../_ruby_mjit_p12u3.exp
+           TODO: Don't discard them on --jit-verbose=2+ */
+        dup2(dev_null, stdout_fileno);
+        exit_code = exec_process(mjit_cc_path, args);
+        dup2(orig_fd, stdout_fileno);
+
+        close(orig_fd);
+        close(dev_null);
+    }
+    free(args);
+
+    if (exit_code != 0)
+        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
+        "-o", NULL, NULL,
+        NULL,
+    };
+    char **args;
+    int len = sizeof(rest_args) / sizeof(const char *);
+
+    rest_args[len - 2] = mjit_header_file;
+    rest_args[len - 3] = mjit_pch_file;
+    verbose(2, "Creating precompiled header");
+    args = form_args(3, CC_COMMON_ARGS, CC_CODEFLAG_ARGS, rest_args);
+    if (args == NULL) {
+        if (mjit_opts.warnings || mjit_opts.verbose)
+            fprintf(stderr, "MJIT warning: making precompiled header failed on forming args\n");
+        CRITICAL_SECTION_START(3, "in make_pch");
+        pch_status = PCH_FAILED;
+        CRITICAL_SECTION_FINISH(3, "in make_pch");
+        return;
+    }
+
+    exit_code = exec_process(mjit_cc_path, args);
+    free(args);
+
+    CRITICAL_SECTION_START(3, "in make_pch");
+    if (exit_code == 0) {
+        pch_status = PCH_SUCCESS;
+    } else {
+        if (mjit_opts.warnings || mjit_opts.verbose)
+            fprintf(stderr, "MJIT warning: Making precompiled header failed on compilation. Stopping MJIT worker...\n");
+        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 1 if it succeeds. (non-mswin) */
+static int
+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] = mjit_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(mjit_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 1 if it succeeds. (non-mswin) */
+static int
+link_o_to_so(const char **o_files, const char *so_file)
+{
+    int exit_code;
+    const char *options[] = {
+        "-o", NULL,
+# ifdef _WIN32
+        mjit_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(mjit_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;
+    struct rb_mjit_unit_node *node;
+    double start_time, end_time;
+    static const char so_ext[] = DLEXT;
+    char so_file[MAXPATHLEN];
+    const char **o_files;
+    int i = 0, success;
+
+    /* Abnormal use case of rb_mjit_unit that doesn't have ISeq */
+    unit = (struct rb_mjit_unit *)calloc(1, sizeof(struct rb_mjit_unit)); /* To prevent GC, don't use ZALLOC */
+    if (unit == NULL) return;
+    unit->id = mjit_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 = (const char **)alloca(sizeof(char *) * (mjit_active_units.length + 1));
+    o_files[mjit_active_units.length] = NULL;
+    CRITICAL_SECTION_START(3, "in compact_all_jit_code to keep .o files");
+    for (node = mjit_active_units.head; node != NULL; node = node->next) {
+        o_files[i] = node->unit->o_file;
+        i++;
+    }
+
+    start_time = real_ms_time();
+    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) {
+            if (mjit_opts.warnings || mjit_opts.verbose)
+                fprintf(stderr, "MJIT warning: failure in loading code from compacted '%s': %s\n", so_file, dlerror());
+            free(unit);
+            return;
+        }
+        unit->handle = handle;
+
+        /* lazily dlclose handle (and .so file for win32) on `mjit_finish()`. */
+        node = (struct rb_mjit_unit_node *)calloc(1, sizeof(struct rb_mjit_unit_node)); /* To prevent GC, don't use ZALLOC */
+        node->unit = unit;
+        add_to_list(node, &mjit_compact_units);
+
+        if (!mjit_opts.save_temps) {
+#  ifdef _WIN32
+            unit->so_file = strdup(so_file); /* lazily delete on `clean_object_files()` */
+#  else
+            remove_file(so_file);
+#  endif
+        }
+
+        CRITICAL_SECTION_START(3, "in compact_all_jit_code to read list");
+        for (node = mjit_active_units.head; node != NULL; node = node->next) {
+            void *func;
+            char funcname[35]; /* TODO: reconsider `35` */
+            sprintf(funcname, "_mjit%d", node->unit->id);
+
+            if ((func = dlsym(handle, funcname)) == NULL) {
+                if (mjit_opts.warnings || mjit_opts.verbose)
+                    fprintf(stderr, "MJIT warning: skipping to reload '%s' from '%s': %s\n", funcname, so_file, dlerror());
+                continue;
+            }
+
+            if (node->unit->iseq) { /* Check whether GCed or not */
+                /* Usage of jit_code might be not in a critical section.  */
+                MJIT_ATOMIC_SET(node->unit->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, mjit_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) {
+        if (mjit_opts.warnings || mjit_opts.verbose)
+            fprintf(stderr, "MJIT warning: failure in loading code from '%s': %s\n", 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)
+{
+    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 = mjit_pch_file;
+    const char *e = header_name_end(s);
+
+    fprintf(f, "#include \"");
+    /* print mjit_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 success;
+    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_finish_hook is called */
+    CRITICAL_SECTION_START(3, "before mjit_compile to wait GC finish");
+    while (mjit_in_gc) {
+        verbose(3, "Waiting wakeup from GC");
+        rb_native_cond_wait(&mjit_gc_wakeup, &mjit_engine_mutex);
+    }
+    mjit_in_jit = TRUE;
+    CRITICAL_SECTION_FINISH(3, "before mjit_compile to wait GC finish");
+
+    {
+        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);
+    }
+    success = mjit_compile(f, unit->iseq->body, funcname);
+
+    /* release blocking mjit_gc_start_hook */
+    CRITICAL_SECTION_START(3, "after mjit_compile to wakeup client for GC");
+    mjit_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)) {
+        const char *o_files[2] = { NULL, NULL };
+        o_files[0] = o_file;
+        success = link_o_to_so(o_files, so_file);
+
+        /* Alwasy set o_file for compaction. The value is also used for lazy deletion. */
+        unit->o_file = strdup(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) {
+#ifdef _WIN32
+        unit->so_file = strdup(so_file); /* lazily delete on `clean_object_files()` */
+#else
+        remove_file(so_file);
+#endif
+    }
+
+    if ((uintptr_t)func > (uintptr_t)LAST_JIT_ISEQ_FUNC) {
+        struct rb_mjit_unit_node *node = create_list_node(unit);
+        CRITICAL_SECTION_START(3, "end of jit");
+        add_to_list(node, &mjit_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;
+}
+
+/* Set to TRUE to stop worker.  */
+int mjit_stop_worker_p;
+/* Set to TRUE if worker is stopped.  */
+int mjit_worker_stopped;
+
+/* 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 mjit_worker_stopped");
+        mjit_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 mjit_worker_stopped");
+        return; /* TODO: do the same thing in the latter half of mjit_finish */
+    }
+
+    /* main worker loop */
+    while (!mjit_stop_worker_p) {
+        struct rb_mjit_unit_node *node;
+
+        /* wait until unit is available */
+        CRITICAL_SECTION_START(3, "in worker dequeue");
+        while ((mjit_unit_queue.head == NULL || mjit_active_units.length > mjit_opts.max_cache_size) && !mjit_stop_worker_p) {
+            rb_native_cond_wait(&mjit_worker_wakeup, &mjit_engine_mutex);
+            verbose(3, "Getting wakeup from client");
+        }
+        node = get_from_list(&mjit_unit_queue);
+        CRITICAL_SECTION_FINISH(3, "in worker dequeue");
+
+        if (node) {
+            mjit_func_t func = convert_unit_to_func(node->unit);
+
+            CRITICAL_SECTION_START(3, "in jit func replace");
+            if (node->unit->iseq) { /* Check whether GCed or not */
+                /* Usage of jit_code might be not in a critical section.  */
+                MJIT_ATOMIC_SET(node->unit->iseq->body->jit_func, func);
+            }
+            remove_from_list(node, &mjit_unit_queue);
+            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 && mjit_unit_queue.length == 0 && mjit_active_units.length > 1)
+                || mjit_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. */
+    mjit_worker_stopped = TRUE;
+}