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Fix race conditions that are possible in Db.

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This is accomplished by locking the entire database, and keeping it locked
until the last reference is unlocked. We get rid of per-reference locks,
because those are what cause race conditions.
This commit is contained in:
Jordan Bancino 2023-04-24 16:19:17 +00:00
parent 313249ca88
commit 279f261aed
1 changed files with 28 additions and 37 deletions
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65
src/Db.c
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@ -75,7 +75,6 @@ struct Db
struct DbRef
{
HashMap *json;
pthread_mutex_t lock;
unsigned long ts;
size_t size;
@ -290,16 +289,7 @@ DbCacheEvict(Db * db)
{
char *hash;
if (pthread_mutex_trylock(&ref->lock) != 0)
{
/* This ref is locked by another thread, don't evict it. */
ref = ref->next;
continue;
}
JsonFree(ref->json);
pthread_mutex_unlock(&ref->lock);
pthread_mutex_destroy(&ref->lock);
hash = DbHashKey(ref->name);
HashMapDelete(db->cache, hash);
@ -338,6 +328,7 @@ Db *
DbOpen(char *dir, size_t cache)
{
Db *db;
pthread_mutexattr_t attr;
if (!dir)
{
@ -353,7 +344,10 @@ DbOpen(char *dir, size_t cache)
db->dir = dir;
db->maxCache = cache;
pthread_mutex_init(&db->lock, NULL);
pthread_mutexattr_init(&attr);
pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
pthread_mutex_init(&db->lock, &attr);
pthread_mutexattr_destroy(&attr);
db->mostRecent = NULL;
db->leastRecent = NULL;
@ -383,6 +377,8 @@ DbMaxCacheSet(Db * db, size_t cache)
return;
}
pthread_mutex_lock(&db->lock);
db->maxCache = cache;
if (db->maxCache && !db->cache)
{
@ -391,6 +387,8 @@ DbMaxCacheSet(Db * db, size_t cache)
}
DbCacheEvict(db);
pthread_mutex_unlock(&db->lock);
}
void
@ -401,10 +399,13 @@ DbClose(Db * db)
return;
}
pthread_mutex_lock(&db->lock);
DbMaxCacheSet(db, 0);
DbCacheEvict(db);
HashMapFree(db->cache);
pthread_mutex_unlock(&db->lock);
pthread_mutex_destroy(&db->lock);
Free(db);
@ -441,8 +442,6 @@ DbLockFromArr(Db * db, Array * args)
{
if (ref)
{
pthread_mutex_lock(&ref->lock);
HashMapDelete(db->cache, hash);
JsonFree(ref->json);
StringArrayFree(ref->name);
@ -472,8 +471,6 @@ DbLockFromArr(Db * db, Array * args)
db->leastRecent = db->mostRecent;
}
pthread_mutex_unlock(&ref->lock);
pthread_mutex_destroy(&ref->lock);
Free(ref);
}
ref = NULL;
@ -499,8 +496,6 @@ DbLockFromArr(Db * db, Array * args)
{
unsigned long diskTs = UtilLastModified(file);
pthread_mutex_lock(&ref->lock);
ref->fd = fd;
ref->stream = stream;
@ -511,7 +506,6 @@ DbLockFromArr(Db * db, Array * args)
if (!json)
{
pthread_mutex_unlock(&ref->lock);
StreamClose(ref->stream);
ref = NULL;
goto finish;
@ -585,9 +579,6 @@ DbLockFromArr(Db * db, Array * args)
ref->fd = fd;
ref->stream = stream;
pthread_mutex_init(&ref->lock, NULL);
pthread_mutex_lock(&ref->lock);
name = ArrayCreate();
for (i = 0; i < ArraySize(args); i++)
{
@ -622,7 +613,10 @@ DbLockFromArr(Db * db, Array * args)
}
finish:
pthread_mutex_unlock(&db->lock);
if (!ref)
{
pthread_mutex_unlock(&db->lock);
}
Free(file);
Free(hash);
@ -654,12 +648,15 @@ DbCreate(Db * db, size_t nArgs,...)
return NULL;
}
pthread_mutex_lock(&db->lock);
file = DbFileName(db, args);
if (UtilLastModified(file))
{
Free(file);
ArrayFree(args);
pthread_mutex_unlock(&db->lock);
return NULL;
}
@ -669,6 +666,7 @@ DbCreate(Db * db, size_t nArgs,...)
Free(file);
ArrayFree(args);
Free(dir);
pthread_mutex_unlock(&db->lock);
return NULL;
}
@ -679,12 +677,16 @@ DbCreate(Db * db, size_t nArgs,...)
if (!fp)
{
ArrayFree(args);
pthread_mutex_unlock(&db->lock);
return NULL;
}
StreamPuts(fp, "{}");
StreamClose(fp);
/* DbLockFromArr() will lock again for us */
pthread_mutex_unlock(&db->lock);
ret = DbLockFromArr(db, args);
ArrayFree(args);
@ -719,8 +721,6 @@ DbDelete(Db * db, size_t nArgs,...)
ref = HashMapGet(db->cache, hash);
if (ref)
{
pthread_mutex_lock(&ref->lock);
HashMapDelete(db->cache, hash);
JsonFree(ref->json);
StringArrayFree(ref->name);
@ -750,8 +750,6 @@ DbDelete(Db * db, size_t nArgs,...)
db->leastRecent = db->mostRecent;
}
pthread_mutex_unlock(&ref->lock);
pthread_mutex_destroy(&ref->lock);
Free(ref);
}
@ -802,8 +800,6 @@ DbUnlock(Db * db, DbRef * ref)
return 0;
}
pthread_mutex_lock(&db->lock);
lseek(ref->fd, 0L, SEEK_SET);
if (ftruncate(ref->fd, 0) < 0)
{
@ -841,15 +837,11 @@ DbUnlock(Db * db, DbRef * ref)
destroy = 1;
}
pthread_mutex_unlock(&ref->lock);
if (destroy)
{
JsonFree(ref->json);
StringArrayFree(ref->name);
pthread_mutex_destroy(&ref->lock);
Free(ref);
}
@ -874,11 +866,6 @@ DbExists(Db * db, size_t nArgs,...)
return 0;
}
/*
* Though it's not explicitly required, we lock the
* database before checking that an object exists to
* prevent any potential race conditions.
*/
pthread_mutex_lock(&db->lock);
file = DbFileName(db, args);
@ -917,12 +904,15 @@ DbList(Db * db, size_t nArgs,...)
path = ArrayFromVarArgs(nArgs, ap);
dir = DbDirName(db, path, 0);
pthread_mutex_lock(&db->lock);
files = opendir(dir);
if (!files)
{
ArrayFree(path);
ArrayFree(result);
Free(dir);
pthread_mutex_unlock(&db->lock);
return NULL;
}
while ((file = readdir(files)))
@ -944,6 +934,7 @@ DbList(Db * db, size_t nArgs,...)
ArrayFree(path);
Free(dir);
pthread_mutex_unlock(&db->lock);
return result;
}