From 1537d6680bb66dc2484e11815bc2cd0e31ca39cc Mon Sep 17 00:00:00 2001 From: Roberto Ierusalimschy Date: Fri, 26 Feb 2021 11:41:02 -0300 Subject: [PATCH] New control for reentrancy of emergency collections 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. --- lgc.c | 36 ++++++++++++++++++++++++------------ lmem.c | 25 ++++++++++++------------- lstate.c | 1 + lstate.h | 1 + testes/gc.lua | 8 ++++++++ 5 files changed, 46 insertions(+), 25 deletions(-) diff --git a/lgc.c b/lgc.c index 94e0486e..b360eed0 100644 --- a/lgc.c +++ b/lgc.c @@ -1575,52 +1575,64 @@ static int sweepstep (lua_State *L, global_State *g, static lu_mem singlestep (lua_State *L) { global_State *g = G(L); + lu_mem work; + lua_assert(!g->gcstopem); /* collector is not reentrant */ + g->gcstopem = 1; /* no emergency collections while collecting */ switch (g->gcstate) { case GCSpause: { restartcollection(g); g->gcstate = GCSpropagate; - return 1; + work = 1; + break; } case GCSpropagate: { if (g->gray == NULL) { /* no more gray objects? */ g->gcstate = GCSenteratomic; /* finish propagate phase */ - return 0; + work = 0; } else - return propagatemark(g); /* traverse one gray object */ + work = propagatemark(g); /* traverse one gray object */ + break; } case GCSenteratomic: { - lu_mem work = atomic(L); /* work is what was traversed by 'atomic' */ + work = atomic(L); /* work is what was traversed by 'atomic' */ entersweep(L); g->GCestimate = gettotalbytes(g); /* first estimate */; - return work; + break; } case GCSswpallgc: { /* sweep "regular" objects */ - return sweepstep(L, g, GCSswpfinobj, &g->finobj); + work = sweepstep(L, g, GCSswpfinobj, &g->finobj); + break; } case GCSswpfinobj: { /* sweep objects with finalizers */ - return sweepstep(L, g, GCSswptobefnz, &g->tobefnz); + work = sweepstep(L, g, GCSswptobefnz, &g->tobefnz); + break; } case GCSswptobefnz: { /* sweep objects to be finalized */ - return sweepstep(L, g, GCSswpend, NULL); + work = sweepstep(L, g, GCSswpend, NULL); + break; } case GCSswpend: { /* finish sweeps */ checkSizes(L, g); g->gcstate = GCScallfin; - return 0; + work = 0; + break; } case GCScallfin: { /* call remaining finalizers */ if (g->tobefnz && !g->gcemergency) { - int n = runafewfinalizers(L, GCFINMAX); - return n * GCFINALIZECOST; + g->gcstopem = 0; /* ok collections during finalizers */ + work = runafewfinalizers(L, GCFINMAX) * GCFINALIZECOST; } else { /* emergency mode or no more finalizers */ g->gcstate = GCSpause; /* finish collection */ - return 0; + work = 0; } + break; } default: lua_assert(0); return 0; } + g->gcstopem = 0; + return work; } diff --git a/lmem.c b/lmem.c index e90f991a..9029d588 100644 --- a/lmem.c +++ b/lmem.c @@ -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' */ } diff --git a/lstate.c b/lstate.c index 04909db3..c5e3b437 100644 --- a/lstate.c +++ b/lstate.c @@ -379,6 +379,7 @@ LUA_API lua_State *lua_newstate (lua_Alloc f, void *ud) { g->panic = NULL; g->gcstate = GCSpause; g->gckind = KGC_INC; + g->gcstopem = 0; g->gcemergency = 0; g->finobj = g->tobefnz = g->fixedgc = NULL; g->firstold1 = g->survival = g->old1 = g->reallyold = NULL; diff --git a/lstate.h b/lstate.h index 0322e2c6..c1283bb6 100644 --- a/lstate.h +++ b/lstate.h @@ -260,6 +260,7 @@ typedef struct global_State { lu_byte currentwhite; lu_byte gcstate; /* state of garbage collector */ lu_byte gckind; /* kind of GC running */ + lu_byte gcstopem; /* stops emergency collections */ lu_byte genminormul; /* control for minor generational collections */ lu_byte genmajormul; /* control for major generational collections */ lu_byte gcrunning; /* true if GC is running */ diff --git a/testes/gc.lua b/testes/gc.lua index 80850f92..2332c939 100644 --- a/testes/gc.lua +++ b/testes/gc.lua @@ -676,6 +676,14 @@ end -- just to make sure assert(collectgarbage'isrunning') +do -- check that the collector is reentrant in incremental mode + setmetatable({}, {__gc = function () + collectgarbage() + end}) + collectgarbage() +end + + collectgarbage(oldmode) print('OK')