Hello,
I could find on this ML archives only a thread about this subject: to
consider the file checksum instead of the timestamp.
Other systems like scons already support this feature and it would be
great to have it for GNU Make too.
I attached a patch against the current CVS to add --use-checksum to
GNU Make, it is just a proof-of-concept but it shows that adding this
feature can really boost a remake.
In this way, simply touching a file will not cause it to be
recompiled, as it was easy to imagine but for example let's say you
modify a comment in the file test.c; using the standard make you will
have to:
test.c -> test.o -> test
Using a checksum you will have only:
test.c -> test.o
because the .o file is unchanged.
This scenario is what surprised me more as it is a very common one and
can save a lot of time at linking time.
The biggest problem is how save information, in the patch the checksum
for file a is saved in the file a.checksum, but I don't think this can
be a reasonable solution; probably hide them in a subdirectory is not
a so bad idea.
Concurrent accesses are not a problem using files, they will be used
almost in the same way as the timestamp information is used now;
anyway, in the worst case the hash will be different and the file will
be recompiled.
Beside use a better algorithm to find a hash for the file, MD5 is my
first thought, and hopefully find another way to store data (but still
I think files are the best choice), do you have other ideas or
suggestions?
Regards,
Giuseppe
? checksum_patch.diff
Index: file.c
===================================================================
RCS file: /sources/make/make/file.c,v
retrieving revision 1.90
diff -u -r1.90 file.c
--- file.c 4 Nov 2007 21:54:01 -0000 1.90
+++ file.c 11 Apr 2008 21:20:54 -0000
@@ -1,6 +1,6 @@
-/* Target file management for GNU Make.
+/* Target file management fo GNU Make.
Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997,
-1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software
+1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software
Foundation, Inc.
This file is part of GNU Make.
@@ -189,8 +189,80 @@
f->last = new;
}
+ new->last_checksum = read_checksum (new);
+
+
return new;
}
+
+
+/* Compute the checksum for the file. */
+
+int
+compute_checksum(struct file *new)
+{
+ int checksum = 0;
+ FILE *f;
+ char buffer [4096];
+
+ f = fopen (new->name, "r");
+ if (f != NULL)
+ {
+ size_t nbr;
+ int i;
+ do
+ {
+ nbr = fread (buffer, 4096, 1, f);
+
+ for (i = 0; i < nbr; i++)
+ checksum = 21 * checksum + 23 * buffer[i];
+
+ }
+ while (nbr);
+ fclose (f);
+ }
+ return checksum;
+}
+
+int
+read_checksum(struct file *new)
+{
+ int checksum = 0;
+ FILE *f;
+ char * checksum_file = (char*) xmalloc (strlen (new->name) + 10);
+
+ sprintf (checksum_file, "%s.checksum", new->name);
+
+ f = fopen (checksum_file, "r");
+ if (f != NULL)
+ {
+ fread (&checksum, 4, 1, f);
+ fclose (f);
+ }
+
+
+ free (checksum_file);
+ return checksum;
+}
+
+void
+write_checksum(struct file *new)
+{
+ FILE *f;
+ char * checksum_file = (char*) xmalloc (strlen (new->name) + 10);
+
+ sprintf (checksum_file, "%s.checksum", new->name);
+
+ f = fopen (checksum_file, "w");
+ if (f != NULL)
+ {
+ fwrite (&new->checksum, 4, 1, f);
+ fclose (f);
+ }
+
+ free (checksum_file);
+}
+
/* Rehash FILE to NAME. This is not as simple as resetting
the `hname' member, since it must be put in a new hash bucket,
Index: filedef.h
===================================================================
RCS file: /sources/make/make/filedef.h,v
retrieving revision 2.30
diff -u -r2.30 filedef.h
--- filedef.h 4 Jul 2007 19:35:18 -0000 2.30
+++ filedef.h 11 Apr 2008 21:20:54 -0000
@@ -1,6 +1,6 @@
/* Definition of target file data structures for GNU Make.
Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997,
-1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software
+1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software
Foundation, Inc.
This file is part of GNU Make.
@@ -94,6 +94,8 @@
pattern-specific variables. */
unsigned int considered:1; /* equal to 'considered' if file has been
considered on current scan of goal chain */
+ int checksum; /* Actual checksum of the file. */
+ int last_checksum; /* Last checksum registered on the file. */
};
@@ -103,6 +105,9 @@
struct file *lookup_file (const char *name);
struct file *enter_file (const char *name);
+int compute_checksum(struct file *new);
+int read_checksum(struct file *new);
+void write_checksum(struct file *new);
struct dep *parse_prereqs (char *prereqs);
void remove_intermediates (int sig);
void snap_deps (void);
Index: main.c
===================================================================
RCS file: /sources/make/make/main.c,v
retrieving revision 1.227
diff -u -r1.227 main.c
--- main.c 4 Nov 2007 21:54:01 -0000 1.227
+++ main.c 11 Apr 2008 21:20:57 -0000
@@ -1,6 +1,6 @@
/* Argument parsing and main program of GNU Make.
Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997,
-1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software
+1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software
Foundation, Inc.
This file is part of GNU Make.
@@ -226,6 +226,12 @@
unsigned int default_job_slots = 1;
static unsigned int master_job_slots = 0;
+
+/* Define if the checksum of a file should be considered. */
+
+int use_checksum = 0;
+
+
/* Value of job_slots that means no limit. */
static unsigned int inf_jobs = 0;
@@ -365,6 +371,8 @@
Consider FILE to be infinitely new.\n"),
N_("\
--warn-undefined-variables Warn when an undefined variable is referenced.\n"),
+ N_("\
+ --use-checksum Use the files checksum.\n"),
NULL
};
@@ -411,6 +419,7 @@
{ 'S', flag_off, &keep_going_flag, 1, 1, 0, 0, &default_keep_going_flag,
"no-keep-going" },
{ 't', flag, &touch_flag, 1, 1, 1, 0, 0, "touch" },
+ { 'U', flag, &use_checksum, 1, 1, 1, 0, 0, "checksum" },
{ 'v', flag, &print_version_flag, 1, 1, 0, 0, 0, "version" },
{ CHAR_MAX+3, string, &verbosity_flags, 1, 1, 0, 0, 0,
"verbosity" },
@@ -432,6 +441,7 @@
{ "new-file", required_argument, 0, 'W' },
{ "assume-new", required_argument, 0, 'W' },
{ "assume-old", required_argument, 0, 'o' },
+ { "use-checksum", optional_argument, 0, 'U' },
{ "max-load", optional_argument, 0, 'l' },
{ "dry-run", no_argument, 0, 'n' },
{ "recon", no_argument, 0, 'n' },
Index: make.h
===================================================================
RCS file: /sources/make/make/make.h,v
retrieving revision 1.131
diff -u -r1.131 make.h
--- make.h 4 Nov 2007 21:54:01 -0000 1.131
+++ make.h 11 Apr 2008 21:20:57 -0000
@@ -517,6 +517,7 @@
extern unsigned int commands_started;
+extern int use_checksum;
extern int handling_fatal_signal;
Index: remake.c
===================================================================
RCS file: /sources/make/make/remake.c,v
retrieving revision 1.137
diff -u -r1.137 remake.c
--- remake.c 5 Nov 2007 14:15:20 -0000 1.137
+++ remake.c 11 Apr 2008 21:20:59 -0000
@@ -1,6 +1,6 @@
/* Basic dependency engine for GNU Make.
Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997,
-1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software
+1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software
Foundation, Inc.
This file is part of GNU Make.
@@ -505,7 +505,6 @@
d->file->dontcare = file->dontcare;
}
-
dep_status |= check_dep (d->file, depth, this_mtime, &maybe_make);
/* Restore original dontcare flag. */
@@ -515,6 +514,7 @@
if (! d->ignore_mtime)
must_make = maybe_make;
+
check_renamed (d->file);
{
@@ -546,6 +546,7 @@
/* Now we know whether this target needs updating.
If it does, update all the intermediate files we depend on. */
+
if (must_make || always_make_flag)
{
for (d = file->deps; d != 0; d = d->next)
@@ -764,6 +765,11 @@
DBF (DB_VERBOSE, _("Recipe of `%s' is being run.\n"));
return 0;
}
+ else if (use_checksum)
+ {
+ file->checksum = compute_checksum (file);
+ write_checksum (file);
+ }
switch (file->update_status)
{
@@ -946,8 +952,31 @@
check_renamed (file);
mtime = file_mtime (file);
check_renamed (file);
- if (mtime == NONEXISTENT_MTIME || mtime > this_mtime)
- *must_make_ptr = 1;
+
+ if (mtime == NONEXISTENT_MTIME)
+ {
+ *must_make_ptr = 1;
+ }
+ else if(mtime > this_mtime)
+ {
+ if (use_checksum && file->last_checksum )
+ {
+ file->checksum = compute_checksum (file);
+
+ if (file->checksum != file->last_checksum)
+ *must_make_ptr = 1;
+
+ }
+ else
+ *must_make_ptr = 1;
+
+ if (use_checksum)
+ {
+ if (!file->checksum)
+ file->checksum = compute_checksum (file);
+ write_checksum (file);
+ }
+ }
}
else
{
@@ -972,10 +1001,33 @@
check_renamed (file);
mtime = file_mtime (file);
check_renamed (file);
- if (mtime != NONEXISTENT_MTIME && mtime > this_mtime)
- /* If the intermediate file actually exists and is newer, then we
- should remake from it. */
- *must_make_ptr = 1;
+ if (mtime != NONEXISTENT_MTIME)
+ {
+ *must_make_ptr = 1;
+ }
+ else if(mtime > this_mtime)
+ {
+ if (use_checksum && file->last_checksum)
+ {
+ file->checksum = compute_checksum (file);
+ if (file->checksum != file->last_checksum)
+ *must_make_ptr = 1;
+ }
+ else
+ /* If the intermediate file actually exists and is newer, then we
+ should remake from it. */
+ *must_make_ptr = 1;
+
+
+ if (use_checksum)
+ {
+ if (!file->checksum)
+ file->checksum = compute_checksum (file);
+ write_checksum (file);
+ }
+
+
+ }
else
{
/* Otherwise, update all non-intermediate files we depend on, if
@@ -1002,20 +1054,20 @@
if (lastd == 0)
{
file->deps = d->next;
- free_dep (d);
+ free_dep (d);
d = file->deps;
}
else
{
lastd->next = d->next;
- free_dep (d);
+ free_dep (d);
d = lastd->next;
}
continue;
}
d->file->parent = file;
- maybe_make = *must_make_ptr;
+ maybe_make = *must_make_ptr;
dep_status |= check_dep (d->file, depth, this_mtime,
&maybe_make);
if (! d->ignore_mtime)
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