Use a single file for the disk cache

This has the advantage that on crash it is automatically cleaned

kitty/constants.py

@@ -142,13 +142,6 @@ def cache_dir() -> str:
     return candidate
 
 
-def dir_for_disk_cache() -> str:
-    from tempfile import mkdtemp
-    ans = os.path.join(cache_dir(), 'disk-cache')
-    os.makedirs(ans, exist_ok=True)
-    return mkdtemp(dir=ans)
-
-
 def wakeup() -> None:
     from .fast_data_types import get_boss
     b = get_boss()

kitty/disk-cache.c

@@ -22,32 +22,27 @@ typedef struct {
     size_t hash_keylen, data_sz;
     bool written_to_disk;
     uint8_t encryption_key[64];
-    char filename[8];
+    off_t pos_in_cache_file;
     UT_hash_handle hh;
 } CacheEntry;
 
 
 typedef struct {
     PyObject_HEAD
-    char *path;
-    int path_fd;
+    char *cache_dir;
+    int cache_file_fd;
     pthread_mutex_t lock;
     pthread_t write_thread;
     bool thread_started, lock_inited, loop_data_inited, shutting_down, fully_initialized;
     LoopData loop_data;
-    PyObject *rmtree;
     CacheEntry *entries, currently_writing;
 } DiskCache;
 
 
 void
-free_cache_entry(const DiskCache *self, CacheEntry *e) {
+free_cache_entry(CacheEntry *e) {
     if (e->hash_key) { free(e->hash_key); e->hash_key = NULL; }
     if (e->data) { free(e->data); e->data = NULL; }
-    if (self->path_fd > -1 && e->filename[0]) {
-        unlinkat(self->path_fd, e->filename, 0);
-        e->filename[0] = 0;
-    }
     free(e);
 }
 
@@ -58,16 +53,27 @@ new(PyTypeObject *type, PyObject UNUSED *args, PyObject UNUSED *kwds) {
     DiskCache *self;
     self = (DiskCache*)type->tp_alloc(type, 0);
     if (self) {
-        self->path_fd = -1;
-        PyObject *shutil = PyImport_ImportModule("shutil");
-        if (!shutil) { Py_CLEAR(self); return NULL; }
-        self->rmtree = PyObject_GetAttrString(shutil, "rmtree");
-        Py_CLEAR(shutil);
-        if (!self->rmtree) { Py_CLEAR(self); return NULL; }
+        self->cache_file_fd = -1;
     }
     return (PyObject*) self;
 }
 
+static int
+open_cache_file(const char *cache_path) {
+    size_t sz = strlen(cache_path) + 16;
+    char *buf = calloc(1, sz);
+    if (!buf) { errno = ENOMEM; return -1; }
+    snprintf(buf, sz - 1, "%s/XXXXXXXXXXXX", cache_path);
+    int fd = -1;
+    while (fd < 0) {
+        fd = mkostemp(buf, O_CLOEXEC);
+        if (fd > -1 || errno != EINTR) break;
+    }
+    if (fd > -1) unlink(buf);
+    free(buf);
+    return fd;
+}
+
 static void*
 write_loop(void *data) {
     DiskCache *self = (DiskCache*)data;
@@ -101,27 +107,24 @@ ensure_state(DiskCache *self) {
         self->thread_started = true;
     }
 
-    if (!self->path) {
+    if (!self->cache_dir) {
         PyObject *kc = NULL, *cache_dir = NULL;
         kc = PyImport_ImportModule("kitty.constants");
         if (kc) {
             cache_dir = PyObject_CallMethod(kc, "dir_for_disk_cache", NULL);
             if (cache_dir) {
-                self->path = strdup(PyUnicode_AsUTF8(cache_dir));
-                if (!self->path) PyErr_NoMemory();
+                self->cache_dir = strdup(PyUnicode_AsUTF8(cache_dir));
+                if (!self->cache_dir) PyErr_NoMemory();
             }
         }
         Py_CLEAR(kc); Py_CLEAR(cache_dir);
         if (PyErr_Occurred()) return false;
     }
 
-    if (self->path_fd < 0) {
-        while (self->path_fd < 0) {
-            self->path_fd = open(self->path, O_DIRECTORY | O_RDWR | O_CLOEXEC);
-            if (self->path_fd > -1 || errno != EINTR) break;
-        }
-        if (self->path_fd < 0) {
-            PyErr_SetFromErrnoWithFilename(PyExc_OSError, self->path);
+    if (self->cache_file_fd < 0) {
+        self->cache_file_fd = open_cache_file(self->cache_dir);
+        if (self->cache_file_fd < 0) {
+            PyErr_SetFromErrnoWithFilename(PyExc_OSError, self->cache_dir);
             return false;
         }
     }
@@ -155,21 +158,16 @@ dealloc(DiskCache* self) {
         CacheEntry *tmp, *s;
         HASH_ITER(hh, self->entries, s, tmp) {
             HASH_DEL(self->entries, s);
-            free_cache_entry(self, s); s = NULL;
+            free_cache_entry(s); s = NULL;
         }
         self->entries = NULL;
     }
-    if (self->path_fd > -1) {
-        safe_close(self->path_fd, __FILE__, __LINE__);
-        self->path_fd = -1;
-    }
-    if (self->path) {
-        PyObject_CallFunction(self->rmtree, "sO", self->path, Py_True);
-        free(self->path); self->path = NULL;
+    if (self->cache_file_fd > -1) {
+        safe_close(self->cache_file_fd, __FILE__, __LINE__);
+        self->cache_file_fd = -1;
     }
     if (self->currently_writing.hash_key) free(self->currently_writing.hash_key);
     if (self->currently_writing.data) free(self->currently_writing.data);
-    Py_CLEAR(self->rmtree);
     Py_TYPE(self)->tp_free((PyObject*)self);
 }
 
@@ -219,36 +217,27 @@ xor_data(const uint8_t* restrict key, const size_t key_sz, uint8_t* restrict dat
 
 static void
 read_from_cache_entry(const DiskCache *self, const CacheEntry *s, uint8_t *dest) {
-    int fd = -1;
-    while (fd < 0) {
-        fd = openat(self->path_fd, s->filename, O_CLOEXEC | O_RDONLY);
-        if (fd > 0 || errno != EINTR) break;
-    }
-    if (fd < 0) {
-        PyErr_SetFromErrnoWithFilename(PyExc_OSError, s->filename);
-        return;
-    }
     uint8_t *p = dest;
     size_t sz = s->data_sz;
+    off_t pos = s->pos_in_cache_file;
     while (sz) {
-        ssize_t n = read(fd, p, sz);
+        ssize_t n = pread(self->cache_file_fd, p, sz, pos);
         if (n > 0) {
             sz -= n;
             p += n;
+            pos += n;
             continue;
         }
         if (n < 0) {
             if (errno == EINTR || errno == EAGAIN) continue;
-            PyErr_SetFromErrnoWithFilename(PyExc_OSError, s->filename);
-            goto end;
+            PyErr_SetFromErrnoWithFilename(PyExc_OSError, self->cache_dir);
+            break;
         }
         if (n == 0) {
             PyErr_SetString(PyExc_OSError, "Disk cache file truncated");
-            goto end;
+            break;
         }
     }
-end:
-    safe_close(fd, __FILE__, __LINE__);
 }
 
 bool