Is it possible to yield/resume the main thread?
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- Subject: Is it possible to yield/resume the main thread?
- From: Stefan <ste@...>
- Date: Fri, 3 Jul 2020 14:49:14 +0200
Hello,
is it possible to yield and resume the main thread, even if the
yielding function runs in another coroutine?
(related: http://lua-users.org/lists/lua-l/2019-05/msg00081.html )
My Lua script runs in an event-driven environment and I need to
halt it to until an external resource is ready. This works really
nice as long as the state is started with lua_resume and the
C callbacks yield back to the "ground" layer of C.
But when the script calls these functions in a coroutine, they just
yield the script's coroutine and don't stop the execution of Lua.
I tried to yield the main thread directly, but resuming it continues
execution at the wrong point:
print 'A'
cb() --> lua_yield(main thread) / Should pause the script
print 'B'
coroutine.resume(coroutine.create(function()
print ' X'
cb() --> lua_yield(main thread) / Should pause the script
print ' Y'
end))
print 'C'
Prints (Y is missing):
[Resume state]
A
[Yielded]
[Resume state]
B
X
[Yielded]
[Resume state]
C
[Finished]
Now my questions are:
A) Can a CFunction call lua_yield with anything other than the
lua_State passed as argument?
B) If not, can the entire script be yielded/resumed directly in
standard Lua?
I'm sorry for the naive questions, but I couldn't find a direct
statement in the manual.
Here is the C test program:
// gcc -Wall -Ilua-5.4.0/src main.c lua-5.4.0/src/liblua.a -ldl -lm
#include <stdio.h>
#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>
lua_State* L;
int luacb(lua_State* T)
{
return lua_yield(L, 0);
}
int main()
{
L = luaL_newstate();
luaL_openlibs(L);
lua_register(L, "cb", luacb);
const char script[] =
"print 'A'\n"
"cb()\n"
"print 'B'\n"
"coroutine.resume(coroutine.create(function()\n"
" print ' X'\n"
" cb()\n"
" print ' Y'\n"
"end))\n"
"print 'C'\n";
if (luaL_loadbufferx (L, script, sizeof script - 1, "script", "t")
!= LUA_OK) {
printf("[Error] %s\n", lua_tostring(L, -1));
goto close_state;
}
for (;;) {
printf("[Resume state]\n");
int nresults = 0;
int lr = lua_resume(L, NULL, 0, &nresults);
switch (lr) {
case LUA_OK:
lua_pop(L, nresults);
printf("[Finished]\n");
goto close_state;
case LUA_YIELD:
lua_pop(L, nresults);
printf("[Yielded]\n");
continue;
default: {
printf("[Error] %s\n", lua_tostring(L, -1));
goto close_state;
}
}
}
close_state:
lua_close(L);
}