jsonfmt: Fix threading support + memory leak bug

c/common.c

@@ -1,43 +1,57 @@
-/* Custom string builder, comparable to functionality provided by SV*
- * functions, but with less magic and better inlineable. */
+/* Custom string builder, should be slightly faster than using Sv* macros directly. */
 
 typedef struct {
-    size_t len;
-    size_t size;
-    char *buf;
+    SV *sv;
+    char *cur;
+    char *end;
 } fustr;
 
-/* No need to call this, an empty fustr is already usable.
- * This allows setting a custom initial size. */
-static void fustr_init(fustr *s, size_t prealloc) {
-    s->len = 0;
-    s->size = prealloc;
-    s->buf = safemalloc(prealloc);
+static void fustr_init_(pTHX_ fustr *s, size_t prealloc) {
+    s->sv = sv_2mortal(newSV(prealloc));
+    SvPOK_only(s->sv);
+    s->cur = SvPVX(s->sv);
+    s->end = SvEND(s->sv);
 }
 
-static void fustr_grow(fustr *s, size_t add) {
-    if (s->size == 0) s->size = 512;
-    while (s->size < s->len + add)
-        s->size *= 2;
-    s->buf = saferealloc(s->buf, s->size);
+static void fustr_grow(pTHX_ fustr *s, size_t add) {
+    size_t off = s->cur - SvPVX(s->sv);
+    size_t newlen = 64;
+    add += off;
+    /* Increment to next power of two; SvGROW's default strategy is slow */
+    while (newlen < add) newlen <<= 1;
+    char *buf = SvGROW(s->sv, newlen);
+    s->cur = buf + off;
+    s->end = buf + SvLEN(s->sv);
 }
 
-#define fustr_reserve(s, n) do {\
-        if (UNLIKELY((s)->size < (s)->len + (n))) fustr_grow(s, n);\
-    } while(0)
+static inline void fustr_reserve_(pTHX_ fustr *s, size_t add) {
+    if (UNLIKELY(s->end < s->cur + add)) fustr_grow(aTHX_ s, add);
+}
 
-#define fustr_write(s, str, n) do {\
-        fustr_reserve(s, n);\
-        memcpy((s)->buf+(s)->len, str, (n));\
-        (s)->len += (n);\
-    } while(0) 
+static inline void fustr_write_(pTHX_ fustr *s, const char *str, size_t n) {
+    fustr_reserve_(aTHX_ s, n);
+    memcpy(s->cur, str, n);
+    s->cur += n;
+}
 
-/* Move the string buffer into a new SV; fustr should be considered invalid after this call.
- * Does not set the UTF8 flag. */
-static SV *fustr_sv(fustr *s) {
-    SV *r = newSV(0);
-    fustr_write(s, "", 1); // trailing nul
-    sv_usepvn_flags(r, s->buf, s->len-1, SV_HAS_TRAILING_NUL);
+/* Adds n uninitialized bytes to the string and returns a buffer to write the data to */
+static inline char *fustr_write_buf_(pTHX_ fustr *s, size_t n) {
+    fustr_reserve_(aTHX_ s, n);
+    char *buf = s->cur;
+    s->cur += n;
+    return buf;
+}
+
+static SV *fustr_done_(pTHX_ fustr *s) {
+    fustr_reserve_(aTHX_ s, 1);
+    *s->cur = 0;
+    SvCUR_set(s->sv, s->cur - SvPVX(s->sv));
     // TODO: SvPV_shrink_to_cur?
-    return r;
+    return s->sv;
 }
+
+#define fustr_init(a,b) fustr_init_(aTHX_ a,b)
+#define fustr_reserve(a,b) fustr_reserve_(aTHX_ a,b)
+#define fustr_write(a,b,c) fustr_write_(aTHX_ a,b,c)
+#define fustr_write_buf(a,b) fustr_write_buf_(aTHX_ a,b)
+#define fustr_done(a) fustr_done_(aTHX_ a)