@matheusbsbs / matheus-bagliano / commits / eaf7e835e6

gitk: Synchronize config file writes

If several gitk instances are closed simultaneously, the savestuff procedure can run at the same time, resulting in a conflict which may cause losing of some of the instance's changes, failing the saving operation or even corrupting the configuration file. This can happen, for example, at user session closing, or at group closing of all instances of an application which is possible in some desktop environments. To avoid this, make sure that only one saving operation is in progress. It is guarded by existence of the $config_file_tmp file. Creating the file and moving it to $config_file are both atomic operations, so it should be reliable. Reading does not need to be syncronized, because moving is an atomic operation, and the $config_file always refers to a full and correct file. But, if there is a stale $config_file_tmp file, report it at gitk start. If such file is detected when saving, just report it abort the save, as for other errors in saving. Signed-off-by: Max Kirillov <max@max630.net> Signed-off-by: Paul Mackerras <paulus@samba.org>

Max Kirillov committed Mar 4, 2015 at 05:58 UTC eaf7e835e61de98488592e02b31da9f44fd4505d
1 file changed +28 -3
gitk
+28 -3
@@ -2783,6 +2783,21 @@ proc doprogupdate {} {
2783 }
2784 }
2785
2786 +proc config_check_tmp_exists {tries_left} {
2787 + global config_file_tmp
2788 +
2789 + if {[file exists $config_file_tmp]} {
2790 + incr tries_left -1
2791 + if {$tries_left > 0} {
2792 + after 100 [list config_check_tmp_exists $tries_left]
2793 + } else {
2794 + error_popup "There appears to be a stale $config_file_tmp\
2795 + file, which will prevent gitk from saving its configuration on exit.\
2796 + Please remove it if it is not being used by any existing gitk process."
2797 + }
2798 + }
2799 +}
2800 +
2801 proc config_init_trace {name} {
2802 global config_variable_changed config_variable_original
2803
@@ -2818,11 +2833,16 @@ proc savestuff {w} {
2833
2834 if {$stuffsaved} return
2835 if {![winfo viewable .]} return
2836 + set remove_tmp 0
2837 if {[catch {
2822 - if {[file exists $config_file_tmp]} {
2823 - file delete -force $config_file_tmp
2838 + set try_count 0
2839 + while {[catch {set f [open $config_file_tmp {WRONLY CREAT EXCL}]}]} {
2840 + if {[incr try_count] > 50} {
2841 + error "Unable to write config file: $config_file_tmp exists"
2842 + }
2843 + after 100
2844 }
2825 - set f [open $config_file_tmp w]
2845 + set remove_tmp 1
2846 if {$::tcl_platform(platform) eq {windows}} {
2847 file attributes $config_file_tmp -hidden true
2848 }
@@ -2884,9 +2904,13 @@ proc savestuff {w} {
2904 puts $f "}"
2905 close $f
2906 file rename -force $config_file_tmp $config_file
2907 + set remove_tmp 0
2908 } err]} {
2909 puts "Error saving config: $err"
2910 }
2911 + if {$remove_tmp} {
2912 + file delete -force $config_file_tmp
2913 + }
2914 set stuffsaved 1
2915 }
2916
@@ -12177,6 +12201,7 @@ catch {
12201 }
12202 source $config_file
12203 }
12204 +config_check_tmp_exists 50
12205
12206 set config_variables {
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