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New control for reentrancy of emergency collections

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Instead of assuming that shrinking a block may be an emergency
collection, use an explicit field ('gcstopem') to stop emergency
collections while GC is working.
This commit is contained in:
Roberto Ierusalimschy
2021-02-26 11:41:02 -03:00
parent e0260eb2d4
commit 1537d6680b
5 changed files with 46 additions and 25 deletions
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25
lmem.c
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@@ -24,12 +24,12 @@
#if defined(EMERGENCYGCTESTS)
/*
** First allocation will fail whenever not building initial state
** and not shrinking a block. (This fail will trigger 'tryagain' and
** a full GC cycle at every allocation.)
** First allocation will fail whenever not building initial state.
** (This fail will trigger 'tryagain' and a full GC cycle at every
** allocation.)
*/
static void *firsttry (global_State *g, void *block, size_t os, size_t ns) {
if (completestate(g) && ns > os)
if (completestate(g) && ns > 0) /* frees never fail */
return NULL; /* fail */
else /* normal allocation */
return (*g->frealloc)(g->ud, block, os, ns);
@@ -138,15 +138,17 @@ void luaM_free_ (lua_State *L, void *block, size_t osize) {
/*
** In case of allocation fail, this function will call the GC to try
** to free some memory and then try the allocation again.
** (It should not be called when shrinking a block, because then the
** interpreter may be in the middle of a collection step.)
** In case of allocation fail, this function will do an emergency
** collection to free some memory and then try the allocation again.
** The GC should not be called while state is not fully built, as the
** collector is not yet fully initialized. Also, it should not be called
** when 'gcstopem' is true, because then the interpreter is in the
** middle of a collection step.
*/
static void *tryagain (lua_State *L, void *block,
size_t osize, size_t nsize) {
global_State *g = G(L);
if (completestate(g)) { /* is state fully build? */
if (completestate(g) && !g->gcstopem) {
luaC_fullgc(L, 1); /* try to free some memory... */
return (*g->frealloc)(g->ud, block, osize, nsize); /* try again */
}
@@ -156,8 +158,6 @@ static void *tryagain (lua_State *L, void *block,
/*
** Generic allocation routine.
** If allocation fails while shrinking a block, do not try again; the
** GC shrinks some blocks and it is not reentrant.
*/
void *luaM_realloc_ (lua_State *L, void *block, size_t osize, size_t nsize) {
void *newblock;
@@ -165,8 +165,7 @@ void *luaM_realloc_ (lua_State *L, void *block, size_t osize, size_t nsize) {
lua_assert((osize == 0) == (block == NULL));
newblock = firsttry(g, block, osize, nsize);
if (l_unlikely(newblock == NULL && nsize > 0)) {
if (nsize > osize) /* not shrinking a block? */
newblock = tryagain(L, block, osize, nsize);
newblock = tryagain(L, block, osize, nsize);
if (newblock == NULL) /* still no memory? */
return NULL; /* do not update 'GCdebt' */
}