Johannes SchindelinFrom: Heiko Voigt <hvoigt@hvoigt.net>
The previous implementation said that the filesystem information on Windows is not reliable to determine whether a file is executable. To gather this information it was peeking into the first two bytes of a file to see whether it looks executable.
Apart from the fact that on Windows executables are defined as such by their extension (and Git has special code to support "executing" scripts when they have a she-bang line) it leads to serious performance problems: not only do we have to open many files now, it gets even slower when a virus scanner is running.
See the following measurements (in seconds) as an example, where we execute a simple program that simply lists the directory contents and calls open() on every listed file:
With virus scanner running (coldcache):
$ ./a.exe /libexec/git-core/ before open (git-add.exe): 0.000000 after open (git-add.exe): 0.412873 before open (git-annotate.exe): 0.000175 after open (git-annotate.exe): 0.397925 before open (git-apply.exe): 0.000243 after open (git-apply.exe): 0.399996 before open (git-archive.exe): 0.000147 after open (git-archive.exe): 0.397783 before open (git-bisect--helper.exe): 0.000160 after open (git-bisect--helper.exe): 0.397700 before open (git-blame.exe): 0.000160 after open (git-blame.exe): 0.399136 ...
With virus scanner running (hotcache):
$ ./a.exe /libexec/git-core/ before open (git-add.exe): 0.000000 after open (git-add.exe): 0.000325 before open (git-annotate.exe): 0.000229 after open (git-annotate.exe): 0.000177 before open (git-apply.exe): 0.000167 after open (git-apply.exe): 0.000150 before open (git-archive.exe): 0.000154 after open (git-archive.exe): 0.000156 before open (git-bisect--helper.exe): 0.000132 after open (git-bisect--helper.exe): 0.000180 before open (git-blame.exe): 0.000718 after open (git-blame.exe): 0.000724 ...
With this patch I get:
$ time git help git Launching default browser to display HTML ...
real 0m8.723s user 0m0.000s sys 0m0.000s
and without
$ time git help git Launching default browser to display HTML ...
real 1m37.734s user 0m0.000s sys 0m0.031s
both tests with cold cache and giving the machine some time to settle down after restart.
Signed-off-by: Heiko Voigt <heiko.voigt@mahr.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> --- Published-As: https://github.com/dscho/git/releases/tag/help-is-exe-v1 Fetch-It-Via: git fetch https://github.com/dscho/git help-is-exe-v1
help.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-)
Show changes to help.c +18 −3
diff --git a/help.c b/help.c index 53e2a67e00..bc6cd19cf3 100644 --- a/help.c +++ b/help.c @@ -105,7 +105,22 @@ static int is_executable(const char *name) return 0; #if defined(GIT_WINDOWS_NATIVE) -{ /* cannot trust the executable bit, peek into the file instead */ + /* + * On Windows there is no executable bit. The file extension + * indicates whether it can be run as an executable, and Git + * has special-handling to detect scripts and launch them + * through the indicated script interpreter. We test for the + * file extension first because virus scanners may make + * it quite expensive to open many files. + */ + if (ends_with(name, ".exe")) + return S_IXUSR; + +{ + /* + * Now that we know it does not have an executable extension, + * peek into the file instead. + */ char buf[3] = { 0 }; int n; int fd = open(name, O_RDONLY); @@ -113,8 +128,8 @@ static int is_executable(const char *name) if (fd >= 0) { n = read(fd, buf, 2); if (n == 2) - /* DOS executables start with "MZ" */ - if (!strcmp(buf, "#!") || !strcmp(buf, "MZ")) + /* look for a she-bang */ + if (!strcmp(buf, "#!")) st.st_mode |= S_IXUSR; close(fd); } base-commit: 4e59582ff70d299f5a88449891e78d15b4b3fabe
-- 2.11.1.windows.prerelease.2.9.g3014b57
