libgo/runtime/go-cgo.c

   1 /* go-cgo.c -- SWIG support routines for libgo.
   2
   3    Copyright 2011 The Go Authors. All rights reserved.
   4    Use of this source code is governed by a BSD-style
   5    license that can be found in the LICENSE file.  */
   6
   7 #include "runtime.h"
   8 #include "go-alloc.h"
   9 #include "interface.h"
  10 #include "go-panic.h"
  11
  12 /* Prepare to call from code written in Go to code written in C or
  13    C++.  This takes the current goroutine out of the Go scheduler, as
  14    though it were making a system call.  Otherwise the program can
  15    lock up if the C code goes to sleep on a mutex or for some other
  16    reason.  This idea is to call this function, then immediately call
  17    the C/C++ function.  After the C/C++ function returns, call
  18    syscall_cgocalldone.  The usual Go code would look like
  19
  20        syscall.Cgocall()
  21        defer syscall.Cgocalldone()
  22        cfunction()
  23
  24    */
  25
  26 /* We let Go code call these via the syscall package.  */
  27 void syscall_cgocall(void) __asm__ (GOSYM_PREFIX "syscall.Cgocall");
  28 void syscall_cgocalldone(void) __asm__ (GOSYM_PREFIX "syscall.CgocallDone");
  29 void syscall_cgocallback(void) __asm__ (GOSYM_PREFIX "syscall.CgocallBack");
  30 void syscall_cgocallbackdone(void) __asm__ (GOSYM_PREFIX "syscall.CgocallBackDone");
  31
  32 void
  33 syscall_cgocall ()
  34 {
  35   M* m;
  36   G* g;
  37
  38   if (runtime_needextram && runtime_cas (&runtime_needextram, 1, 0))
  39     runtime_newextram ();
  40
  41   m = runtime_m ();
  42   ++m->ncgocall;
  43   g = runtime_g ();
  44   ++g->ncgo;
  45   runtime_entersyscall ();
  46 }
  47
  48 /* Prepare to return to Go code from C/C++ code.  */
  49
  50 void
  51 syscall_cgocalldone ()
  52 {
  53   G* g;
  54
  55   g = runtime_g ();
  56   __go_assert (g != NULL);
  57   --g->ncgo;
  58   if (g->ncgo == 0)
  59     {
  60       /* We are going back to Go, and we are not in a recursive call.
  61          Let the garbage collector clean up any unreferenced
  62          memory.  */
  63       g->cgomal = NULL;
  64     }
  65
  66   /* If we are invoked because the C function called _cgo_panic, then
  67      _cgo_panic will already have exited syscall mode.  */
  68   if (g->status == Gsyscall)
  69     runtime_exitsyscall ();
  70 }
  71
  72 /* Call back from C/C++ code to Go code.  */
  73
  74 void
  75 syscall_cgocallback ()
  76 {
  77   M *mp;
  78
  79   mp = runtime_m ();
  80   if (mp == NULL)
  81     {
  82       runtime_needm ();
  83       mp = runtime_m ();
  84       mp->dropextram = true;
  85     }
  86
  87   runtime_exitsyscall ();
  88
  89   mp = runtime_m ();
  90   if (mp->needextram)
  91     {
  92       mp->needextram = 0;
  93       runtime_newextram ();
  94     }
  95 }
  96
  97 /* Prepare to return to C/C++ code from a callback to Go code.  */
  98
  99 void
 100 syscall_cgocallbackdone ()
 101 {
 102   M *mp;
 103
 104   runtime_entersyscall ();
 105   mp = runtime_m ();
 106   if (mp->dropextram && runtime_g ()->ncgo == 0)
 107     {
 108       mp->dropextram = false;
 109       runtime_dropm ();
 110     }
 111 }
 112
 113 /* Allocate memory and save it in a list visible to the Go garbage
 114    collector.  */
 115
 116 void *
 117 alloc_saved (size_t n)
 118 {
 119   void *ret;
 120   G *g;
 121   CgoMal *c;
 122
 123   ret = __go_alloc (n);
 124
 125   g = runtime_g ();
 126   c = (CgoMal *) __go_alloc (sizeof (CgoMal));
 127   c->next = g->cgomal;
 128   c->alloc = ret;
 129   g->cgomal = c;
 130
 131   return ret;
 132 }
 133
 134 /* These are routines used by SWIG.  The gc runtime library provides
 135    the same routines under the same name, though in that case the code
 136    is required to import runtime/cgo.  */
 137
 138 void *
 139 _cgo_allocate (size_t n)
 140 {
 141   void *ret;
 142
 143   runtime_exitsyscall ();
 144   ret = alloc_saved (n);
 145   runtime_entersyscall ();
 146   return ret;
 147 }
 148
 149 extern const struct __go_type_descriptor string_type_descriptor
 150   __asm__ (GOSYM_PREFIX "__go_tdn_string");
 151
 152 void
 153 _cgo_panic (const char *p)
 154 {
 155   intgo len;
 156   unsigned char *data;
 157   String *ps;
 158   struct __go_empty_interface e;
 159
 160   runtime_exitsyscall ();
 161   len = __builtin_strlen (p);
 162   data = alloc_saved (len);
 163   __builtin_memcpy (data, p, len);
 164   ps = alloc_saved (sizeof *ps);
 165   ps->str = data;
 166   ps->len = len;
 167   e.__type_descriptor = &string_type_descriptor;
 168   e.__object = ps;
 169
 170   /* We don't call runtime_entersyscall here, because normally what
 171      will happen is that we will walk up the stack to a Go deferred
 172      function that calls recover.  However, this will do the wrong
 173      thing if this panic is recovered and the stack unwinding is
 174      caught by a C++ exception handler.  It might be possible to
 175      handle this by calling runtime_entersyscall in the personality
 176      function in go-unwind.c.  FIXME.  */
 177
 178   __go_panic (e);
 179 }