feat(lsm): introduce entry handles for concurrent access

lsm/include/lsm/store.h

@@ -21,27 +21,10 @@ typedef enum lsm_attr_type : uint64_t {
 } lsm_attr_type;
 
 /**
- * An entry inside an LSM store.
+ * A handle referencing an entry inside a store. Read/write operations from/to
- *
+ * the entry go through this handle.
- * Each entry consists of the key it's stored behind, zero  or more attributes
- * (metadata) and a data field. The data field can be stored on disk or
- * in-memory, depending on the size.
  */
-typedef struct lsm_entry lsm_entry;
+typedef struct lsm_entry_handle lsm_entry_handle;
-
-/**
- * Allocate and initialize a new lsm_entry object.
- *
- * @param ptr where to store newly allocated pointer
- */
-lsm_error lsm_entry_init(lsm_entry **ptr);
-
-/**
- * Deallocate an existing lsm_entry object.
- *
- * @param entry object to deallocate
- */
-void lsm_entry_free(lsm_entry *entry);
 
 /**
  * Checks whether the entry has an attribute with the specified type.
@@ -49,7 +32,7 @@ void lsm_entry_free(lsm_entry *entry);
  * @param entry entry to check
  * @param type type of attribute to check for
  */
-bool lsm_entry_attr_present(lsm_entry *entry, lsm_attr_type type);
+bool lsm_entry_attr_present(lsm_entry_handle *handle, lsm_attr_type type);
 
 /**
  * Retrieve the contents of an attribute from an entry, if present
@@ -58,7 +41,7 @@ bool lsm_entry_attr_present(lsm_entry *entry, lsm_attr_type type);
  * @param entry entry to search for
  * @param type type of attribute to return
  */
-lsm_error lsm_entry_attr_get(lsm_str **out, lsm_entry *entry,
+lsm_error lsm_entry_attr_get(lsm_str **out, lsm_entry_handle *handle,
                              lsm_attr_type type);
 
 /**
@@ -68,7 +51,7 @@ lsm_error lsm_entry_attr_get(lsm_str **out, lsm_entry *entry,
  * @param type type of attribute to add
  * @param data data of attribute; ownership of pointer is taken over
  */
-lsm_error lsm_entry_attr_insert(lsm_entry *entry, lsm_attr_type type,
+lsm_error lsm_entry_attr_insert(lsm_entry_handle *handle, lsm_attr_type type,
                                 lsm_str *data);
 
 /**
@@ -79,7 +62,7 @@ lsm_error lsm_entry_attr_insert(lsm_entry *entry, lsm_attr_type type,
  * @param entry entry to remove attribute from
  * @param type type of attribute to remove
  */
-lsm_error lsm_entry_attr_remove(lsm_str **out, lsm_entry *entry,
+lsm_error lsm_entry_attr_remove(lsm_str **out, lsm_entry_handle *handle,
                                 lsm_attr_type type);
 
 /**
@@ -104,7 +87,7 @@ lsm_error lsm_store_init(lsm_store **ptr);
  * @param db_path path to the database file
  * @param data_path path to the data directory
  */
-lsm_error lsm_store_open(lsm_store **ptr, lsm_str *db_path, lsm_str *data_path);
+lsm_error lsm_store_load(lsm_store **ptr, lsm_str *db_path, lsm_str *data_path);
 
 /**
  * Dealocate an existing lsm_store object.
@@ -114,43 +97,45 @@ lsm_error lsm_store_open(lsm_store **ptr, lsm_str *db_path, lsm_str *data_path);
 void lsm_store_free(lsm_store *store);
 
 /**
- * Retrieve an entry from the store, preparing & locking it for the purpose of
+ * Open a read handle to the given entry. This entry must be properly closed
- * reading.
+ * using `lsm_store_handle_close`.
  *
- * @param out pointer to store entry pointer
+ * @param out pointer to store handle pointer
  * @param store store to retrieve entry from
  * @param key key to search
  */
-lsm_error lsm_store_get_read(lsm_entry **out, lsm_store *store, lsm_str *key);
+lsm_error lsm_store_open_read(lsm_entry_handle **out, lsm_store *store,
+                              lsm_str *key);
 
 /**
- * Retrieve an entry from the store for the purposes of writing. This
+ * Open a write handle to the given entry.  This entry must be properly closed
- * write-locks the entry.
+ * using `lsm_store_handle_close`.
  *
- * @param out pointer to store entry pointer
+ * @param out pointer to store handle pointer
  * @param store store to retrieve entry from
  * @param key key to search
  */
-lsm_error lsm_store_get_write(lsm_entry **out, lsm_store *store, lsm_str *key);
+lsm_error lsm_store_open_write(lsm_entry_handle **out, lsm_store *store,
+                               lsm_str *key);
 
 /**
- * Unlock a locked entry.
+ * Close an open entry handle.
  *
- * @param store store to unlock entry in
+ * @param store store the handle's entry is stored in
- * @param entry entry to unlock
+ * @param handle handle to close
  */
-lsm_error lsm_store_unlock(lsm_store *store, lsm_entry *entry);
+void lsm_entry_close(lsm_entry_handle *handle);
 
 /**
- * Allocate a new entry in the store with the specified key. The entry returned
+ * Insert a new entry into the store, returning a write handle to the newly
- * will be write-locked, and should be unlocked after streaming the necessary
+ * created entry.
- * data.
  *
  * @param out pointer to store new entry pointer in
  * @param store store to modify
  * @param key key to add; ownership of key pointer is taken over
  */
-lsm_error lsm_store_insert(lsm_entry **out, lsm_store *store, lsm_str *key);
+lsm_error lsm_store_insert(lsm_entry_handle **out, lsm_store *store,
+                           lsm_str *key);
 
 /**
  * Append new data to the given entry, which is expected to be in the store.
@@ -162,7 +147,7 @@ lsm_error lsm_store_insert(lsm_entry **out, lsm_store *store, lsm_str *key);
  * @param entry entry to append data to
  * @param data data to append
  */
-lsm_error lsm_store_data_write(lsm_store *store, lsm_entry *entry,
+lsm_error lsm_entry_data_append(lsm_store *store, lsm_entry_handle *handle,
                                 lsm_str *data);
 
 #endif

lsm/src/_include/lsm/store_internal.h

@@ -13,7 +13,14 @@ typedef struct lsm_attr {
   lsm_str *str;
 } lsm_attr;
 
-struct lsm_entry {
+/**
+ * An entry inside an LSM store.
+ *
+ * Each entry consists of the key it's stored behind, zero  or more attributes
+ * (metadata) and a data field. The data field can be stored on disk or
+ * in-memory, depending on the size.
+ */
+typedef struct lsm_entry {
   lsm_str *key;
   struct {
     uint64_t count;
@@ -28,7 +35,21 @@ struct lsm_entry {
     } value;
     bool on_disk;
   } data;
-};
+} lsm_entry;
+
+/**
+ * Allocate and initialize a new lsm_entry object.
+ *
+ * @param ptr where to store newly allocated pointer
+ */
+lsm_error lsm_entry_init(lsm_entry **ptr);
+
+/**
+ * Deallocate an existing lsm_entry object.
+ *
+ * @param entry object to deallocate
+ */
+void lsm_entry_free(lsm_entry *entry);
 
 typedef struct lsm_entry_wrapper {
   pthread_rwlock_t lock;
@@ -36,6 +57,14 @@ typedef struct lsm_entry_wrapper {
 } lsm_entry_wrapper;
 
 lsm_error lsm_entry_wrapper_init(lsm_entry_wrapper **ptr);
+void lsm_entry_wrapper_free(lsm_entry_wrapper *wrapper);
+
+struct lsm_entry_handle {
+  lsm_entry_wrapper *wrapper;
+  FILE *f;
+};
+
+lsm_error lsm_entry_handle_init(lsm_entry_handle **out);
 
 struct lsm_store {
   lsm_trie *trie;

lsm/src/store/lsm_store.c

@@ -27,7 +27,7 @@ lsm_error lsm_store_init(lsm_store **ptr) {
   return lsm_error_ok;
 }
 
-lsm_error lsm_store_open(lsm_store **ptr, lsm_str *db_path,
+lsm_error lsm_store_load(lsm_store **ptr, lsm_str *db_path,
                          lsm_str *data_path) {
   lsm_store *store;
   LSM_RES(lsm_store_init(&store));
@@ -42,12 +42,13 @@ lsm_error lsm_store_open(lsm_store **ptr, lsm_str *db_path,
   return lsm_error_ok;
 }
 
-lsm_error lsm_store_get_read(lsm_entry **out, lsm_store *store, lsm_str *key) {
+lsm_error lsm_store_open_read(lsm_entry_handle **out, lsm_store *store,
+                              lsm_str *key) {
   lsm_entry_wrapper *wrapper;
 
   LSM_RES(lsm_trie_search((void **)&wrapper, store->trie, key));
 
-  // We don't want to block the thread
+  // Try to get a read lock on the entry's lock
   if (pthread_rwlock_tryrdlock(&wrapper->lock) != 0) {
     return lsm_error_lock_busy;
   }
@@ -62,8 +63,17 @@ lsm_error lsm_store_get_read(lsm_entry **out, lsm_store *store, lsm_str *key) {
     return lsm_error_not_found;
   }
 
+  lsm_entry_handle *handle;
+  lsm_error res = lsm_entry_handle_init(&handle);
+
+  if (res != lsm_error_ok) {
+    pthread_rwlock_unlock(&wrapper->lock);
+
+    return res;
+  }
+
   // Open a new file descriptor if needed
-  if (entry->data.on_disk && (entry->data.value.file == NULL)) {
+  if (entry->data.on_disk) {
     char path[store->data_path->len + entry->key->len + 2];
     sprintf(path, "%s/%s", lsm_str_ptr(store->data_path),
             lsm_str_ptr(entry->key));
@@ -71,36 +81,111 @@ lsm_error lsm_store_get_read(lsm_entry **out, lsm_store *store, lsm_str *key) {
     FILE *f = fopen(path, "rb");
 
     if (f == NULL) {
+      free(handle);
+
       return lsm_error_failed_io;
     }
 
-    entry->data.value.file = f;
+    handle->f = f;
   }
 
+  handle->wrapper = wrapper;
+  *out = handle;
+
   return lsm_error_ok;
 }
 
-lsm_error lsm_store_insert(lsm_entry **out, lsm_store *store, lsm_str *key) {
+lsm_error lsm_store_open_write(lsm_entry_handle **out, lsm_store *store,
+                               lsm_str *key) {
+  lsm_entry_wrapper *wrapper;
+
+  LSM_RES(lsm_trie_search((void **)&wrapper, store->trie, key));
+
+  // Try to get a write lock on the entry's lock
+  // TODO make this timeout to not block
+  if (pthread_rwlock_wrlock(&wrapper->lock) != 0) {
+    return lsm_error_lock_busy;
+  }
+
+  lsm_entry *entry = wrapper->entry;
+
+  // While the trie's data field will never be NULL, the actual entry pointer
+  // might be
+  if (entry == NULL) {
+    pthread_rwlock_unlock(&wrapper->lock);
+
+    return lsm_error_not_found;
+  }
+
+  lsm_entry_handle *handle;
+  lsm_error res = lsm_entry_handle_init(&handle);
+
+  if (res != lsm_error_ok) {
+    pthread_rwlock_unlock(&wrapper->lock);
+
+    return res;
+  }
+
+  // Open a new file descriptor if needed
+  if (entry->data.on_disk) {
+    char path[store->data_path->len + entry->key->len + 2];
+    sprintf(path, "%s/%s", lsm_str_ptr(store->data_path),
+            lsm_str_ptr(entry->key));
+
+    FILE *f = fopen(path, "wb");
+
+    if (f == NULL) {
+      free(handle);
+
+      return lsm_error_failed_io;
+    }
+
+    handle->f = f;
+  }
+
+  handle->wrapper = wrapper;
+  *out = handle;
+
+  return lsm_error_ok;
+}
+
+lsm_error lsm_store_insert(lsm_entry_handle **out, lsm_store *store,
+                           lsm_str *key) {
+  // TODO what happens when two inserts to the same key happen at the same time?
   lsm_entry_wrapper *wrapper;
   LSM_RES(lsm_entry_wrapper_init(&wrapper));
+  pthread_rwlock_wrlock(&wrapper->lock);
+
+  lsm_error res = lsm_trie_insert(store->trie, key, wrapper);
+
+  // Check if entry isn't already present in advance
+  if (res != lsm_error_ok) {
+    lsm_entry_wrapper_free(wrapper);
+
+    return res;
+  }
 
   lsm_entry *entry;
   LSM_RES(lsm_entry_init(&entry));
 
   entry->key = key;
   wrapper->entry = entry;
-  pthread_rwlock_wrlock(&wrapper->lock);
 
-  // TODO mem leak if already present
+  lsm_entry_handle *handle;
-  LSM_RES(lsm_trie_insert(store->trie, key, wrapper));
+  LSM_RES(lsm_entry_handle_init(&handle));
 
-  *out = entry;
+  // No need to set the handle's file, as the entry doesn't have any data yet
+  handle->wrapper = wrapper;
+
+  *out = handle;
 
   return lsm_error_ok;
 }
 
-lsm_error lsm_store_data_write(lsm_store *store, lsm_entry *entry,
+lsm_error lsm_entry_data_append(lsm_store *store, lsm_entry_handle *handle,
                                 lsm_str *data) {
+  lsm_entry *entry = handle->wrapper->entry;
+
   uint64_t new_len = entry->data.len + lsm_str_len(data);
   const char *data_s = lsm_str_ptr(data);
 
@@ -124,13 +209,13 @@ lsm_error lsm_store_data_write(lsm_store *store, lsm_entry *entry,
       sprintf(path, "%s/%s", lsm_str_ptr(store->data_path),
               lsm_str_ptr(entry->key));
 
-      FILE *f = fopen(path, "w");
+      FILE *f = fopen(path, "ab");
 
       if (f == NULL) {
         return lsm_error_failed_io;
       }
 
-      entry->data.value.file = f;
+      handle->f = f;
       entry->data.on_disk = true;
 
       // TODO free old buff, write original data to file
@@ -141,7 +226,7 @@ lsm_error lsm_store_data_write(lsm_store *store, lsm_entry *entry,
     // TODO what happens when I/O fails?
     while (written < data->len) {
       written += fwrite(&data_s[written], sizeof(char), data->len - written,
-                        entry->data.value.file);
+                        handle->f);
     }
   }
 

lsm/src/store/lsm_store_entry.c

@@ -32,16 +32,40 @@ lsm_error lsm_entry_wrapper_init(lsm_entry_wrapper **ptr) {
   return lsm_error_ok;
 }
 
-bool lsm_entry_attr_present(lsm_entry *entry, lsm_attr_type type) {
+void lsm_entry_wrapper_free(lsm_entry_wrapper *wrapper) { free(wrapper); }
-  return (entry->attrs.bitmap & type) != 0;
+
+lsm_error lsm_entry_handle_init(lsm_entry_handle **out) {
+  lsm_entry_handle *handle = calloc(1, sizeof(lsm_entry_handle));
+
+  if (handle == NULL) {
+    return lsm_error_failed_alloc;
   }
 
-lsm_error lsm_entry_attr_get(lsm_str **out, lsm_entry *entry,
+  *out = handle;
+
+  return lsm_error_ok;
+}
+
+void lsm_entry_close(lsm_entry_handle *handle) {
+  if (handle->f != NULL) {
+    fclose(handle->f);
+  }
+
+  pthread_rwlock_unlock(&handle->wrapper->lock);
+  free(handle);
+}
+
+bool lsm_entry_attr_present(lsm_entry_handle *handle, lsm_attr_type type) {
+  return (handle->wrapper->entry->attrs.bitmap & type) != 0;
+}
+
+lsm_error lsm_entry_attr_get(lsm_str **out, lsm_entry_handle *handle,
                              lsm_attr_type type) {
-  if (!lsm_entry_attr_present(entry, type)) {
+  if (!lsm_entry_attr_present(handle, type)) {
     return lsm_error_not_found;
   }
 
+  lsm_entry *entry = handle->wrapper->entry;
   uint64_t i = 0;
 
   while (entry->attrs.items[i].type != type) {
@@ -53,12 +77,14 @@ lsm_error lsm_entry_attr_get(lsm_str **out, lsm_entry *entry,
   return lsm_error_ok;
 }
 
-lsm_error lsm_entry_attr_remove(lsm_str **out, lsm_entry *entry,
+lsm_error lsm_entry_attr_remove(lsm_str **out, lsm_entry_handle *handle,
                                 lsm_attr_type type) {
-  if (!lsm_entry_attr_present(entry, type)) {
+  if (!lsm_entry_attr_present(handle, type)) {
     return lsm_error_not_found;
   }
 
+  lsm_entry *entry = handle->wrapper->entry;
+
   if (entry->attrs.count == 1) {
     *out = entry->attrs.items[0].str;
 
@@ -99,12 +125,14 @@ lsm_error lsm_entry_attr_remove(lsm_str **out, lsm_entry *entry,
   return lsm_error_ok;
 }
 
-lsm_error lsm_entry_attr_insert(lsm_entry *entry, lsm_attr_type type,
+lsm_error lsm_entry_attr_insert(lsm_entry_handle *handle, lsm_attr_type type,
                                 lsm_str *data) {
-  if (lsm_entry_attr_present(entry, type)) {
+  if (lsm_entry_attr_present(handle, type)) {
     return lsm_error_already_present;
   }
 
+  lsm_entry *entry = handle->wrapper->entry;
+
   lsm_attr *new_attrs =
       realloc(entry->attrs.items, (entry->attrs.count + 1) * sizeof(lsm_attr));