diff options
author | Mark H Weaver <mhw@netris.org> | 2012-01-18 02:53:05 -0500 |
---|---|---|
committer | Mark H Weaver <mhw@netris.org> | 2012-01-21 03:23:02 -0500 |
commit | ad432bc8317c33899efc29854550b67f3d7babf7 (patch) | |
tree | fb43ba58394dac9137a78d9424673b440f8b1c33 | |
parent | d47db067b63089880e2e202d5a33fd7fe5e41dbe (diff) | |
download | guile-ad432bc8317c33899efc29854550b67f3d7babf7.tar.gz |
Universally-unique gensyms
* libguile/symbols.c (scm_gensym): Make the gensym counter a 128-bit
thread-local, initialized to a random number upon the first call to
`gensym' within a given thread. This counter is rendered as a 22 byte
suffix of mostly base64 digits.
* libguile/threads.h (scm_i_thread): Add a thread-local gensym_counter.
* libguile/threads.c (guilify_self_1): Initialize gensym_counter to NULL.
-rw-r--r-- | libguile/symbols.c | 50 | ||||
-rw-r--r-- | libguile/threads.c | 1 | ||||
-rw-r--r-- | libguile/threads.h | 4 |
3 files changed, 44 insertions, 11 deletions
diff --git a/libguile/symbols.c b/libguile/symbols.c index 59aca002e..840a458af 100644 --- a/libguile/symbols.c +++ b/libguile/symbols.c @@ -31,6 +31,7 @@ #include "libguile/variable.h" #include "libguile/alist.h" #include "libguile/fluids.h" +#include "libguile/threads.h" #include "libguile/strings.h" #include "libguile/vectors.h" #include "libguile/hashtab.h" @@ -340,7 +341,9 @@ SCM_DEFINE (scm_string_ci_to_symbol, "string-ci->symbol", 1, 0, 0, /* The default prefix for `gensym'd symbols. */ static SCM default_gensym_prefix; -#define MAX_PREFIX_LENGTH 30 +#define GENSYM_LENGTH 22 /* bytes */ +#define GENSYM_RADIX_BITS 6 +#define GENSYM_RADIX (1 << (GENSYM_RADIX_BITS)) SCM_DEFINE (scm_gensym, "gensym", 0, 1, 0, (SCM prefix), @@ -351,22 +354,47 @@ SCM_DEFINE (scm_gensym, "gensym", 0, 1, 0, "resetting the counter.") #define FUNC_NAME s_scm_gensym { - static int gensym_counter = 0; - + static const char base64[GENSYM_RADIX] = + "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789$@"; + static const char base4[4] = "_.-~"; + + unsigned char *digit_buf = SCM_I_CURRENT_THREAD->gensym_counter; + char char_buf[GENSYM_LENGTH]; SCM suffix, name; - int n, n_digits; - char buf[SCM_INTBUFLEN]; + int i; if (SCM_UNBNDP (prefix)) prefix = default_gensym_prefix; - /* mutex in case another thread looks and incs at the exact same moment */ - scm_i_scm_pthread_mutex_lock (&scm_i_misc_mutex); - n = gensym_counter++; - scm_i_pthread_mutex_unlock (&scm_i_misc_mutex); + if (SCM_UNLIKELY (digit_buf == NULL)) + { + /* This is the first time gensym has been called in this thread. + Allocate and randomize our new thread-local gensym counter */ + digit_buf = (unsigned char *) + scm_gc_malloc_pointerless (GENSYM_LENGTH, "gensym-counter"); + scm_i_random_bytes_from_platform (digit_buf, GENSYM_LENGTH); + for (i = (GENSYM_LENGTH - 1); i >= 0; --i) + digit_buf[i] &= (GENSYM_RADIX - 1); + SCM_I_CURRENT_THREAD->gensym_counter = digit_buf; + } + + /* Increment our thread-local gensym_counter. */ + for (i = (GENSYM_LENGTH - 1); i >= 0; --i) + { + if (SCM_LIKELY (++(digit_buf[i]) < GENSYM_RADIX)) + break; + else + digit_buf[i] = 0; + } + + /* Encode digit_buf as base64, except for the first character where we + use the sparse glyphs "_.-~" (base 4) to provide some visual + separation between the prefix and the dense base64 block. */ + for (i = (GENSYM_LENGTH - 1); i > 0; --i) + char_buf[i] = base64[digit_buf[i]]; + char_buf[0] = base4[digit_buf[0] & 3]; - n_digits = scm_iint2str (n, 10, buf); - suffix = scm_from_latin1_stringn (buf, n_digits); + suffix = scm_from_latin1_stringn (char_buf, GENSYM_LENGTH); name = scm_string_append (scm_list_2 (prefix, suffix)); return scm_string_to_symbol (name); } diff --git a/libguile/threads.c b/libguile/threads.c index 5a13e5ccf..67834ffc8 100644 --- a/libguile/threads.c +++ b/libguile/threads.c @@ -545,6 +545,7 @@ guilify_self_1 (struct GC_stack_base *base) t.join_queue = SCM_EOL; t.dynamic_state = SCM_BOOL_F; t.dynwinds = SCM_EOL; + t.gensym_counter = NULL; t.active_asyncs = SCM_EOL; t.block_asyncs = 1; t.pending_asyncs = 1; diff --git a/libguile/threads.h b/libguile/threads.h index ec129bc72..3660a58d4 100644 --- a/libguile/threads.h +++ b/libguile/threads.h @@ -81,6 +81,10 @@ typedef struct scm_i_thread { SCM dynamic_state; SCM dynwinds; + /* Thread-local gensym counter. + */ + unsigned char *gensym_counter; + /* For system asyncs. */ SCM active_asyncs; /* The thunks to be run at the next |