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[or-cvs] r17161: {tor} Document some dmalloc stuff and some stupid C tricks. (tor/trunk/src/common)
Author: nickm
Date: 2008-10-27 12:30:52 -0400 (Mon, 27 Oct 2008)
New Revision: 17161
Modified:
tor/trunk/src/common/compat.h
tor/trunk/src/common/util.c
tor/trunk/src/common/util.h
Log:
Document some dmalloc stuff and some stupid C tricks.
Modified: tor/trunk/src/common/compat.h
===================================================================
--- tor/trunk/src/common/compat.h 2008-10-27 15:04:45 UTC (rev 17160)
+++ tor/trunk/src/common/compat.h 2008-10-27 16:30:52 UTC (rev 17161)
@@ -137,10 +137,20 @@
#define ATTR_NONNULL(x)
/** Macro: Evaluates to <b>exp</b> and hints the compiler that the value
- * of <b>exp</b> will probably be true. */
+ * of <b>exp</b> will probably be true.
+ *
+ * In other words, "if (PREDICT_LIKELY(foo))" is the same as "if (foo)",
+ * except that it tells the compiler that the branch will be taken most of the
+ * time. This can generate slightly better code with some CPUs.
+ */
#define PREDICT_LIKELY(exp) __builtin_expect((exp), 1)
/** Macro: Evaluates to <b>exp</b> and hints the compiler that the value
- * of <b>exp</b> will probably be false. */
+ * of <b>exp</b> will probably be false.
+ *
+ * In other words, "if (PREDICT_UNLIKELY(foo))" is the same as "if (foo)",
+ * except that it tells the compiler that the branch will usually not be
+ * taken. This can generate slightly better code with some CPUs.
+ */
#define PREDICT_UNLIKELY(exp) __builtin_expect((exp), 0)
#else
#define ATTR_NORETURN
@@ -153,9 +163,12 @@
#define PREDICT_UNLIKELY(exp) (exp)
#endif
-/* Ways to declare macros. */
+/** Expands to a syntactically valid empty statement. */
#define STMT_NIL (void)0
+
#ifdef __GNUC__
+/** STMT_BEGIN and STMT_END are used to wrap blocks inside macros so that
+ * the macro can be used as if it were a single C statement. */
#define STMT_BEGIN (void) ({
#define STMT_END })
#elif defined(sun) || defined(__sun__)
@@ -180,8 +193,13 @@
#endif
#ifdef _MSC_VER
+/** Casts the uint64_t value in <b>a</b> to the right type for an argument
+ * to printf. */
#define U64_PRINTF_ARG(a) (a)
+/** Casts the uint64_t* value in <b>a</b> to the right type for an argument
+ * to scanf. */
#define U64_SCANF_ARG(a) (a)
+/** Expands to a literal uint64_t-typed constant for the value <b>n</b>. */
#define U64_LITERAL(n) (n ## ui64)
#else
#define U64_PRINTF_ARG(a) ((long long unsigned int)(a))
@@ -190,6 +208,8 @@
#endif
#if defined(_MSC_VER) || defined(__MINGW32__) || defined(__MINGW64__)
+/** The formatting string used to put a uint64_t value in a printf() or
+ * scanf() function. See also U64_PRINTF_ARG and U64_SCANF_ARG. */
#define U64_FORMAT "%I64u"
#else
#define U64_FORMAT "%llu"
@@ -220,6 +240,9 @@
return tor_memmem(haystack, hlen, needle, strlen(needle));
}
+/* This cast-to-uchar, then-cast-to-int business is needed to compile and
+ * run properly on some Solarises. */
+
#define TOR_ISALPHA(c) isalpha((int)(unsigned char)(c))
#define TOR_ISALNUM(c) isalnum((int)(unsigned char)(c))
#define TOR_ISSPACE(c) isspace((int)(unsigned char)(c))
Modified: tor/trunk/src/common/util.c
===================================================================
--- tor/trunk/src/common/util.c 2008-10-27 15:04:45 UTC (rev 17160)
+++ tor/trunk/src/common/util.c 2008-10-27 16:30:52 UTC (rev 17161)
@@ -83,6 +83,7 @@
#ifdef USE_DMALLOC
#undef strndup
#include <dmalloc.h>
+ /* Macro to pass the extra dmalloc args to another function. */
#define DMALLOC_FN_ARGS , file, line
#if defined(HAVE_DMALLOC_STRDUP)
@@ -95,9 +96,7 @@
#endif
#else /* not using dmalloc */
- #define DMALLOC_FUNC_MALLOC 0
- #define DMALLOC_FUNC_REALLOC 0
#define DMALLOC_FN_ARGS
#endif
@@ -114,7 +113,7 @@
void *result;
#ifndef MALLOC_ZERO_WORKS
- /* Some libcs don't do the right thing on size==0. Override them. */
+ /* Some libc mallocs don't work when size==0. Override them. */
if (size==0) {
size=1;
}
@@ -143,6 +142,12 @@
void *
_tor_malloc_zero(size_t size DMALLOC_PARAMS)
{
+ /* You may ask yourself, "wouldn't it be smart to use calloc instead of
+ * malloc+memset? Perhaps libc's calloc knows some nifty optimization trick
+ * we don't!" Indeed it does, but its optimizations are only a big win when
+ * we're allocating something very big (it knows if it just got the memory
+ * from the OS in a pre-zeroed state). We don't want to use tor_malloc_zero
+ * for big stuff, so we don't bother with calloc. */
void *result = _tor_malloc(size DMALLOC_FN_ARGS);
memset(result, 0, size);
return result;
@@ -182,7 +187,7 @@
#ifdef USE_DMALLOC
dup = dmalloc_strdup(file, line, s, 0);
-#else
+#else
dup = strdup(s);
#endif
if (PREDICT_UNLIKELY(dup == NULL)) {
@@ -213,8 +218,8 @@
return dup;
}
-/** Allocate a chunk of <b>len</b> bytes, with the same contents starting at
- * <b>mem</b>. */
+/** Allocate a chunk of <b>len</b> bytes, with the same contents as the
+ * <b>len</b> bytes starting at <b>mem</b>. */
void *
_tor_memdup(const void *mem, size_t len DMALLOC_PARAMS)
{
Modified: tor/trunk/src/common/util.h
===================================================================
--- tor/trunk/src/common/util.h 2008-10-27 15:04:45 UTC (rev 17160)
+++ tor/trunk/src/common/util.h 2008-10-27 16:30:52 UTC (rev 17161)
@@ -39,8 +39,11 @@
* security-critical properties.
*/
#error "Sorry; we don't support building with NDEBUG."
-#elif defined(__GNUC__)
-/* Give an int-valued version of !x that won't confuse PREDICT_UNLIKELY. */
+#endif
+
+#if defined(__GNUC__)
+/* Give an int-valued version of !x that won't confuse PREDICT_UNLIKELY,
+ * which does poorly with pointer types on some versions of glibc. */
#define IS_FALSE_AS_INT(x) ((x) == ((typeof(x)) 0))
#else
#define IS_FALSE_AS_INT(x) !(x)
@@ -57,6 +60,11 @@
abort(); \
} STMT_END
+/* If we're building with dmalloc, we want all of our memory allocation
+ * functions to take an extra file/line pair of arguments. If not, not.
+ * We define DMALLOC_PARAMS to the extra parameters to insert in the
+ * function prototypes, and DMALLOC_ARGS to the extra arguments to add
+ * to calls. */
#ifdef USE_DMALLOC
#define DMALLOC_PARAMS , const char *file, const int line
#define DMALLOC_ARGS , _SHORT_FILE_, __LINE__
@@ -91,6 +99,13 @@
} \
STMT_END
#else
+/** Release memory allocated by tor_malloc, tor_realloc, tor_strdup, etc.
+ * Unlike the free() function, tor_free() will still work on NULL pointers,
+ * and it sets the pointer value to NULL after freeing it.
+ *
+ * This is a macro. If you need a function pointer to release memory from
+ * tor_malloc(), use _tor_free().
+ */
#define tor_free(p) STMT_BEGIN \
if (PREDICT_LIKELY((p)!=NULL)) { \
free(p); \