TODO: Fix crashing inside luajit on :perform() when curl is built with threads

[msva]

^

[rocaltair]

It will crash while calling lcurl_easy_create in lua coroutine, even in PUC lua.
@msva
@moteus

see
https://github.com/Lua-cURL/Lua-cURLv3/blob/master/src/lceasy.c#L44
do not save lua_State(may be a thread state in coroutine) as a arg in callback.
You need mainthread while invoke callback.

in lua5.2 or later

lua_State * get_main_thread(lua_State *L)
{
lua_rawgeti(L, LUA_REGISTRYINDEX, LUA_RIDX_MAINTHREAD);
lua_State *mL = lua_tothread(L,-1);
lua_pop(L,1);
return mL;
}

Here's the fix

Index: lcurl/lceasy.c
===================================================================
--- lcurl/lceasy.c      (revision 4935)
+++ lcurl/lceasy.c      (revision 4936)
@@ -15,7 +15,9 @@
 #include "lchttppost.h"
 #include "lcshare.h"
 #include <memory.h>
+#include <assert.h>

+#define MAIN_THREAD_NAME "__main_thread__"
 static const char *LCURL_ERROR_TAG = "LCURL_ERROR_TAG";

 #define LCURL_EASY_NAME LCURL_PREFIX" Easy"
@@ -27,11 +29,33 @@
 #  define LCURL_E_UNKNOWN_OPTION CURLE_UNKNOWN_TELNET_OPTION
 #endif

+static void init_main_thread(lua_State *L) {
+  int r;
+  int top = lua_gettop(L);
+  lua_getglobal(L, MAIN_THREAD_NAME);
+  if (lua_isnil(L, -1)) {
+         r = lua_pushthread(L);
+         assert(r == 1);
+         lua_setglobal(L, MAIN_THREAD_NAME);
+  }
+  lua_settop(L, top);
+}
+
+static lua_State * get_main_thread(lua_State *L) {
+  lua_State *l = NULL;
+  lua_getglobal(L, MAIN_THREAD_NAME);
+  l = lua_tothread(L, -1);
+  lua_pop(L, 1);
+  return l;
+}
+
+
 //{

 int lcurl_easy_create(lua_State *L, int error_mode){
   lcurl_easy_t *p;
   int i;
+  lua_State *mainL = get_main_thread(L);

   lua_settop(L, 1); /* options */

@@ -41,7 +65,7 @@

   p->err_mode    = error_mode;
   if(!p->curl) return lcurl_fail_ex(L, p->err_mode, LCURL_ERROR_EASY, CURLE_FAILED_INIT);
-  p->L           = L;
+  p->L           = mainL;
   p->storage     = lcurl_storage_init(L);
   p->wr.cb_ref   = p->wr.ud_ref = LUA_NOREF;
   p->rd.cb_ref   = p->rd.ud_ref = LUA_NOREF;
@@ -1035,6 +1059,7 @@
   /* Hack. We ensure that lcurl_easy_t and lcurl_hpost_stream_t
      compatiable for readfunction
   */
+  init_main_thread(L);
   LCURL_STATIC_ASSERT(offsetof(lcurl_easy_t, L)       == offsetof(lcurl_hpost_stream_t, L));
   LCURL_STATIC_ASSERT(offsetof(lcurl_easy_t, rd)      == offsetof(lcurl_hpost_stream_t, rd));
   LCURL_STATIC_ASSERT(offsetof(lcurl_easy_t, rbuffer) == offsetof(lcurl_hpost_stream_t, rbuffer));
@@ -1044,4 +1069,4 @@
   lua_pop(L, 1);

   lcurl_util_set_const(L, lcurl_easy_opt);
}

[moteus]

I think good solution should invoke callback not in main thread but in thread where perform was called. I really do not remember code right now, but i will look at this in few days.

[rocaltair]

@moteus
glad to hear that.

In my opinion.
Some framework of reactor model, such as luv (libuv for lua), or libevent.
Callbacks are invoked in main thread, in this case, it's not easy to get the coroutine should be resumed in main thread. because callbacks are invoked in C, instead of lua.
and if so, newbies would be traped here.
maybe it's very terrible to find crashing because of script.

We did like I said for 8 years or more in our projects(such as https://itunes.apple.com/cn/app/da-hua-xi-you-2015zui-shou/id1015364140?mt=8).

function getURL(multi, url)
        local co = coroutine.running()
        local easy = lcurl.easy()
        -- ...
        easy:setopt_writefunction(function(data)
                xpcall(function()
                        coroutine.resume(co, data)
                end, __G_TRACE_BACK__)
        end)
        multi:add(easy)
        return coroutine.yield(co)
end

function getUrlInCoroutine(multi, url)
        local function cofunc()
                local data = getURL(multi, url)
                -- ...
        end 
        local co = coroutine.create(cofunc)
        coroutine.resume(co)
end

function main()
        local multi = lcurl.multi()
        getUrlInCoroutine(multi, url1)
        getUrlInCoroutine(multi, url2)
        getUrlInCoroutine(multi, url3)
        -- main loop
        multi:perform() -- how to get the coroutine ?
end

[moteus]

My libuv binding calls callback from thread where uv.run() was called. Just need way store somewhere lua_State when call perform on C side.
It can be done via table like {[multi]=coroutine.running()} but implemented in C and stored in registry

[moteus]

Checkout this PR #63

[rocaltair]

perfect!