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hashtable: Redesign the hashtable API.

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This was intended to make the API public, so SDL_hashtable.h got an extreme
documentation makeover, but for now this remains a private header.

This makes several significant interface changes to SDL_HashTable, and
improves code that makes use of it in various ways.

- The ability to make "stackable" tables is removed. Apparently this still
  worked with the current implementation, but I could see a future
  implementation struggle mightily to support this. It'll be better for
  something external to build on top of the table if it needs it, inserting a
  linked list of stacked items as the hash values and managing them separately.
  There was only one place in SDL using this, unnecessarily, and that has also
  been cleaned up to not need it.
- You no longer specify "buckets" when creating a table, but rather an
  estimated number of items the table is meant to hold. The bucket count was
  crucial to our classic hashtable implementation, but meant less once we
  moved to an Open Addressing implementation anyhow, since the bucket count
  isn't static (and they aren't really "buckets" anymore either). Now you
  can just report how many items you think the hash will hold and SDL will
  allocate a reasonable default for you...or 0 to not guess, and SDL will
  start small and grow as necessary, which is often the correct thing to do.
- There's no more SDL_IterateHashTableKey because there's no more "stackable"
  hash tables.
- SDL_IterateHashTable() now uses a callback, which matches other parts of SDL,
  and also lets us hold the read-lock for the entire iteration and get rid of
  the goofy iterator state variable.
- SDL_InsertIntoHashTable() now lets you specify whether to replace existing
  keys or fail if the key already exists.
- Callbacks now use SDL conventions (userdata as the first param).
- Other naming convention fixes.

I discovered we use a lot of hash tables in SDL3 internally. :) So the bulk
of this work is fixing up that code to use the new interfaces, and simplifying
things (like checking for an item to remove it if it already exists before
inserting a replacement...just do the insert atomically, it'll do all that
for you!).
This commit is contained in:
Ryan C. Gordon
2025-02-13 16:13:43 -05:00
parent 4a9b579195
commit 84a236c92e
13 changed files with 1344 additions and 866 deletions
Download Patch File Download Diff File Expand all files Collapse all files

130
src/stdlib/SDL_getenv.c
View File

@@ -53,7 +53,7 @@ static char **environ;
struct SDL_Environment
{
SDL_Mutex *lock;
SDL_Mutex *lock; // !!! FIXME: reuse SDL_HashTable's lock.
SDL_HashTable *strings;
};
static SDL_Environment *SDL_environment;
@@ -88,13 +88,13 @@ SDL_Environment *SDL_CreateEnvironment(bool populated)
return NULL;
}
env->strings = SDL_CreateHashTable(NULL, 16, SDL_HashString, SDL_KeyMatchString, SDL_NukeFreeKey, false, false);
env->strings = SDL_CreateHashTable(0, false, SDL_HashString, SDL_KeyMatchString, SDL_DestroyHashKey, NULL);
if (!env->strings) {
SDL_free(env);
return NULL;
}
// Don't fail if we can't create a mutex (e.g. on a single-thread environment)
// Don't fail if we can't create a mutex (e.g. on a single-thread environment) // !!! FIXME: single-threaded environments should still return a non-NULL, do-nothing object here. Check for failure!
env->lock = SDL_CreateMutex();
if (populated) {
@@ -114,7 +114,7 @@ SDL_Environment *SDL_CreateEnvironment(bool populated)
}
*value++ = '\0';
SDL_InsertIntoHashTable(env->strings, variable, value);
SDL_InsertIntoHashTable(env->strings, variable, value, true);
}
FreeEnvironmentStringsW(strings);
}
@@ -138,7 +138,7 @@ SDL_Environment *SDL_CreateEnvironment(bool populated)
}
*value++ = '\0';
SDL_InsertIntoHashTable(env->strings, variable, value);
SDL_InsertIntoHashTable(env->strings, variable, value, true);
}
}
#endif // SDL_PLATFORM_WINDOWS
@@ -170,6 +170,49 @@ const char *SDL_GetEnvironmentVariable(SDL_Environment *env, const char *name)
return result;
}
typedef struct CountEnvStringsData
{
size_t count;
size_t length;
} CountEnvStringsData;
static bool SDLCALL CountEnvStrings(void *userdata, const SDL_HashTable *table, const void *key, const void *value)
{
CountEnvStringsData *data = (CountEnvStringsData *) userdata;
data->length += SDL_strlen((const char *) key) + 1 + SDL_strlen((const char *) value) + 1;
data->count++;
return true; // keep iterating.
}
typedef struct CopyEnvStringsData
{
char **result;
char *string;
size_t count;
} CopyEnvStringsData;
static bool SDLCALL CopyEnvStrings(void *userdata, const SDL_HashTable *table, const void *vkey, const void *vvalue)
{
CopyEnvStringsData *data = (CopyEnvStringsData *) userdata;
const char *key = (const char *) vkey;
const char *value = (const char *) vvalue;
size_t len;
len = SDL_strlen(key);
data->result[data->count] = data->string;
SDL_memcpy(data->string, key, len);
data->string += len;
*(data->string++) = '=';
len = SDL_strlen(value);
SDL_memcpy(data->string, value, len);
data->string += len;
*(data->string++) = '\0';
data->count++;
return true; // keep iterating.
}
char **SDL_GetEnvironmentVariables(SDL_Environment *env)
{
char **result = NULL;
@@ -181,40 +224,20 @@ char **SDL_GetEnvironmentVariables(SDL_Environment *env)
SDL_LockMutex(env->lock);
{
size_t count, length = 0;
void *iter;
const char *key, *value;
// First pass, get the size we need for all the strings
count = 0;
iter = NULL;
while (SDL_IterateHashTable(env->strings, (const void **)&key, (const void **)&value, &iter)) {
length += SDL_strlen(key) + 1 + SDL_strlen(value) + 1;
++count;
}
CountEnvStringsData countdata = { 0, 0 };
SDL_IterateHashTable(env->strings, CountEnvStrings, &countdata);
// Allocate memory for the strings
result = (char **)SDL_malloc((count + 1) * sizeof(*result) + length);
char *string = (char *)(result + count + 1);
// Second pass, copy the strings
count = 0;
iter = NULL;
while (SDL_IterateHashTable(env->strings, (const void **)&key, (const void **)&value, &iter)) {
size_t len;
result[count] = string;
len = SDL_strlen(key);
SDL_memcpy(string, key, len);
string += len;
*string++ = '=';
len = SDL_strlen(value);
SDL_memcpy(string, value, len);
string += len;
*string++ = '\0';
++count;
result = (char **)SDL_malloc((countdata.count + 1) * sizeof(*result) + countdata.length);
if (result) {
// Second pass, copy the strings
char *string = (char *)(result + countdata.count + 1);
CopyEnvStringsData cpydata = { result, string, 0 };
SDL_IterateHashTable(env->strings, CopyEnvStrings, &cpydata);
SDL_assert(countdata.count == cpydata.count);
result[cpydata.count] = NULL;
}
result[count] = NULL;
}
SDL_UnlockMutex(env->lock);
@@ -235,26 +258,23 @@ bool SDL_SetEnvironmentVariable(SDL_Environment *env, const char *name, const ch
SDL_LockMutex(env->lock);
{
const void *existing_value;
bool insert = true;
if (SDL_FindInHashTable(env->strings, name, &existing_value)) {
if (!overwrite) {
result = true;
insert = false;
} else {
SDL_RemoveFromHashTable(env->strings, name);
}
}
if (insert) {
char *string = NULL;
if (SDL_asprintf(&string, "%s=%s", name, value) > 0) {
size_t len = SDL_strlen(name);
string[len] = '\0';
name = string;
value = string + len + 1;
result = SDL_InsertIntoHashTable(env->strings, name, value);
char *string = NULL;
if (SDL_asprintf(&string, "%s=%s", name, value) > 0) {
const size_t len = SDL_strlen(name);
string[len] = '\0';
const char *origname = name;
name = string;
value = string + len + 1;
result = SDL_InsertIntoHashTable(env->strings, name, value, overwrite);
if (!result) {
SDL_free(string);
if (!overwrite) {
const void *existing_value = NULL;
// !!! FIXME: InsertIntoHashTable does this lookup too, maybe we should have a means to report that, to avoid duplicate work?
if (SDL_FindInHashTable(env->strings, origname, &existing_value)) {
result = true; // it already existed, and we refused to overwrite it. Call it success.
}
}
}
}
}