New mechanism to query GC parameters

lapi.c

@@ -1217,11 +1217,12 @@ LUA_API int lua_gc (lua_State *L, int what, ...) {
       luaC_changemode(L, KGC_INC);
       break;
     }
-    case LUA_GCSETPARAM: {
+    case LUA_GCPARAM: {
       int param = va_arg(argp, int);
       int value = va_arg(argp, int);
       api_check(L, 0 <= param && param < LUA_GCPN, "invalid parameter");
       res = luaO_applyparam(g->gcparams[param], 100);
+      if (value >= 0)
         g->gcparams[param] = luaO_codeparam(value);
       break;
     }

lbaselib.c

@@ -199,10 +199,10 @@ static int pushmode (lua_State *L, int oldmode) {
 static int luaB_collectgarbage (lua_State *L) {
   static const char *const opts[] = {"stop", "restart", "collect",
     "count", "step", "isrunning", "generational", "incremental",
-    "setparam", NULL};
+    "param", NULL};
   static const char optsnum[] = {LUA_GCSTOP, LUA_GCRESTART, LUA_GCCOLLECT,
     LUA_GCCOUNT, LUA_GCSTEP, LUA_GCISRUNNING, LUA_GCGEN, LUA_GCINC,
-    LUA_GCSETPARAM};
+    LUA_GCPARAM};
   int o = optsnum[luaL_checkoption(L, 1, "collect", opts)];
   switch (o) {
     case LUA_GCCOUNT: {
@@ -231,7 +231,7 @@ static int luaB_collectgarbage (lua_State *L) {
     case LUA_GCINC: {
       return pushmode(L, lua_gc(L, o));
     }
-    case LUA_GCSETPARAM: {
+    case LUA_GCPARAM: {
       static const char *const params[] = {
         "minormul", "majorminor", "minormajor",
         "pause", "stepmul", "stepsize", NULL};
@@ -239,7 +239,7 @@ static int luaB_collectgarbage (lua_State *L) {
         LUA_GCPMINORMUL, LUA_GCPMAJORMINOR, LUA_GCPMINORMAJOR,
         LUA_GCPPAUSE, LUA_GCPSTEPMUL, LUA_GCPSTEPSIZE};
       int p = pnum[luaL_checkoption(L, 2, NULL, params)];
-      lua_Integer value = luaL_checkinteger(L, 3);
+      lua_Integer value = luaL_optinteger(L, 3, -1);
       lua_pushinteger(L, lua_gc(L, o, p, (int)value));
       return 1;
     }

lua.h

@@ -338,7 +338,7 @@ LUA_API void (lua_warning)  (lua_State *L, const char *msg, int tocont);
 #define LUA_GCISRUNNING		6
 #define LUA_GCGEN		7
 #define LUA_GCINC		8
-#define LUA_GCSETPARAM		9
+#define LUA_GCPARAM		9
 
 
 /*

manual/manual.of

@@ -3345,9 +3345,9 @@ Changes the collector to generational mode.
 Returns the previous mode (@id{LUA_GCGEN} or @id{LUA_GCINC}).
 }
 
-@item{@defid{LUA_GCSETPARAM} (int param, int value)|
-Changes the values of a parameter of the collector and returns
-the previous value of that parameter.
+@item{@defid{LUA_GCPARAM} (int param, int val)|
+Changes and/or returns the value of a parameter of the collector.
+If @id{val} is negative, the call only returns the current value.
 The argument @id{param} must have one of the following values:
 @description{
 @item{@defid{LUA_GCPMINORMUL}| The minor multiplier. }
@@ -6390,13 +6390,12 @@ Changes the collector mode to incremental and returns the previous mode.
 Changes the collector mode to generational and returns the previous mode.
 }
 
-@item{@St{setparam}|
-Changes the values of a parameter of the collector and returns
-the previous value of that parameter.
-This option must be followed by two extra arguments:
-The name of the parameter being changed (a string)
-and the new value for that parameter (an integer).
-The argument @id{param} must have one of the following values:
+@item{@St{param}|
+Changes and/or retrieves the values of a parameter of the collector.
+This option must be followed by one or two extra arguments:
+The name of the parameter being changed or retrieved (a string)
+and an optional new value for that parameter (an integer).
+The first argument must have one of the following values:
 @description{
 @item{@St{minormul}| The minor multiplier. }
 @item{@St{majorminor}| The major-minor multiplier. }
@@ -6405,6 +6404,10 @@ The argument @id{param} must have one of the following values:
 @item{@St{stepmul}| The step multiplier. }
 @item{@St{stepsize}| The step size. }
 }
+The call always returns the previous value of the parameter.
+If the call does not give a new value,
+the value is left unchanged.
+
 Lua rounds these values before storing them;
 so, the value returned as the previous value may not be
 exactly the last value set.
@@ -9298,7 +9301,7 @@ declare a local variable with the same name in the loop body.
 @item{
 Parameters for the garbage collection are not set
 with the options @St{incremental} and @St{generational};
-instead, there is a new option @St{setparam} to that end.
+instead, there is a new option @St{param} to that end.
 Moreover, there were some changes in the parameters themselves.
 }
 
@@ -9327,7 +9330,7 @@ to signal the end of the dump.
 @item{
 Parameters for the garbage collection are not set
 with the options @Lid{LUA_GCINC} and @Lid{LUA_GCGEN};
-instead, there is a new option @Lid{LUA_GCSETPARAM} to that end.
+instead, there is a new option @Lid{LUA_GCPARAM} to that end.
 Moreover, there were some changes in the parameters themselves.
 }
 

testes/gc.lua

@@ -28,19 +28,21 @@ end
 -- test weird parameters to 'collectgarbage'
 do
   collectgarbage("incremental")
-  local opause = collectgarbage("setparam", "pause", 100)
-  local ostepmul = collectgarbage("setparam", "stepmul", 100)
+  local opause = collectgarbage("param", "pause", 100)
+  local ostepmul = collectgarbage("param", "stepmul", 100)
+  assert(collectgarbage("param", "pause") == 100)
+  assert(collectgarbage("param", "stepmul") == 100)
   local t = {0, 2, 10, 90, 500, 5000, 30000, 0x7ffffffe}
   for i = 1, #t do
-    collectgarbage("setparam", "pause", t[i])
+    collectgarbage("param", "pause", t[i])
     for j = 1, #t do
-      collectgarbage("setparam", "stepmul", t[j])
+      collectgarbage("param", "stepmul", t[j])
       collectgarbage("step", t[j])
     end
   end
   -- restore original parameters
-  collectgarbage("setparam", "pause", opause)
-  collectgarbage("setparam", "stepmul", ostepmul)
+  collectgarbage("param", "pause", opause)
+  collectgarbage("param", "stepmul", ostepmul)
   collectgarbage()
 end
 

testes/gengc.lua

@@ -163,15 +163,17 @@ assert(collectgarbage'isrunning')
 
 
 do  print"testing stop-the-world collection"
-  local step = collectgarbage("setparam", "stepsize", 0);
+  local step = collectgarbage("param", "stepsize", 0);
   collectgarbage("incremental")
+  assert(collectgarbage("param", "stepsize") == 0)
 
   -- each step does a complete cycle
   assert(collectgarbage("step"))
   assert(collectgarbage("step"))
 
   -- back to default value
-  collectgarbage("setparam", "stepsize", step);
+  collectgarbage("param", "stepsize", step);
+  assert(collectgarbage("param", "stepsize") == step)
 end
 
 collectgarbage(oldmode)