Avoid collisions between parallel [...], take 2

Corinna Vinschen corinna-cygwin@cygwin.com
Thu Oct 29 15:17:00 GMT 2009

On Oct 22 13:55, Corinna Vinschen wrote:
> Ok, so, after all the discussions, this is the patch which comes
> out of it.  [...]

I just created the matching documentation, see below.  I hope that's

Is there anything else which holds up the inclusion of this patch?


Index: doc/new-features.sgml
RCS file: /cvs/src/src/winsup/doc/new-features.sgml,v
retrieving revision 1.21
diff -u -p -r1.21 new-features.sgml
--- doc/new-features.sgml	28 Oct 2009 10:09:54 -0000	1.21
+++ doc/new-features.sgml	29 Oct 2009 15:15:25 -0000
@@ -325,6 +325,14 @@
   delete, to support the toolchain in implementing full C++ standards
   conformance when working with shared libraries.
+- Different Cygwin installations in different paths can be run in parallel
+  without knowing of each other.  The path of the Cygwin DLL used in a
+  process is a key used when creating IPC objects.  So different Cygwin
+  DLLs are running in different namespaces.
+- Each Cygwin DLL stores its path and installation key in the registry.
+  This allows to troubleshoot problems which could be a result of having
+  multiple concurrent Cygwin installations.
Index: utils/utils.sgml
RCS file: /cvs/src/src/winsup/utils/utils.sgml,v
retrieving revision 1.79
diff -u -p -r1.79 utils.sgml
--- utils/utils.sgml	22 Jul 2009 10:20:26 -0000	1.79
+++ utils/utils.sgml	29 Oct 2009 15:15:25 -0000
@@ -13,13 +13,18 @@ command-line utilities support the <lite
 <sect2 id="cygcheck"><title>cygcheck</title>
-Usage: cygcheck PROGRAM [ -v ] [ -h ]
-       cygcheck -c [ PACKAGE ... ] [ -d ]
-       cygcheck -s [ -r ] [ -v ] [ -h ]
+Usage: cygcheck [-v] [-h] PROGRAM
+       cygcheck -c [-d] [PACKAGE]
+       cygcheck -s [-r] [-v] [-h]
        cygcheck -k
-       cygcheck -f FILE [ FILE ... ]
-       cygcheck -l [ PACKAGE ... ]
+       cygcheck -f FILE [FILE]...
+       cygcheck -l [PACKAGE]...
        cygcheck -p REGEXP
+       cygcheck --delete-orphaned-installation-keys
+       cygcheck --enable-unique-object-names Cygwin-DLL
+       cygcheck --disable-unique-object-names Cygwin-DLL
+       cygcheck --show-unique-object-names Cygwin-DLL
+       cygcheck -h
 List system information, check installed packages, or query package database.
 At least one command option or a PROGRAM is required, as shown above.
@@ -36,6 +41,19 @@ At least one command option or a PROGRAM
   -l, --list-package   list contents of PACKAGE (or all packages if none given)
   -p, --package-query  search for REGEXP in the entire cygwin.com package
                        repository (requires internet connectivity)
+  --delete-orphaned-installation-keys
+                       Delete installation keys of old, now unused
+                       installations from the registry.  Requires the right
+                       to change the registry.
+  --enable-unique-object-names Cygwin-DLL
+  --disable-unique-object-names Cygwin-DLL
+  --show-unique-object-names Cygwin-DLL
+                       Enable, disable, or show the setting of the
+                       \"unique object names\" setting in the Cygwin DLL
+                       given as argument to this option.  The DLL path must
+                       be given as valid Windows(!) path.
+                       See the users guide for more information.
+                       If you don't know what this means, don't change it.
   -v, --verbose        produce more verbose output
   -h, --help           annotate output with explanatory comments when given
                        with another command, otherwise print this help
@@ -184,6 +202,65 @@ for example:</para>
 <prompt>$</prompt> <userinput>cygcheck -s -v -r -h > cygcheck_output.txt</userinput>
+Each Cygwin DLL stores its path and installation key in the registry.
+This allows to troubleshoot problems which could be a result of having
+multiple concurrent Cygwin installations.  However, if you're experimenting
+a lot with different Cygwin installation paths, your registry could 
+accumulate a lot of old Cygwin installation entries for which the
+installation doesn't exist anymore.  To get rid of these orphaned registry
+entries, use the <command>cygcheck --delete-orphaned-installation-keys</command>
+Each Cygwin DLL generates a key value from its installation path.  This
+value is not only stored in the registry, it's also used to generate
+global object names used for interprocess communication.   This allows
+to keep different Cygwin installations separate.  Processes running
+under a Cygwin DLL installed in C:\cygwin don't see processes running
+under a Cygwin DLL installed in C:\Program Files\cygwin.  This allows
+to run multiple versions of Cygwin DLLs without these versions to
+interfere with each other, or to run small third-party installations
+for a specific purpose independently from a Cygwin net distribution.
+For debugging purposes it could be desired that the various Cygwin DLLs
+use the same key, independently from their installation paths.  If the
+DLLs have different versions, trying to run processes under these DLLs
+concurrently will result in error messages like this one:</para>
+*** shared version mismatch detected - 0x8A88009C/0x75BE0074.
+This problem is probably due to using incompatible versions of the cygwin DLL.
+Search for cygwin1.dll using the Windows Start->Find/Search facility
+and delete all but the most recent version.  The most recent version *should*
+reside in x:\\cygwin\\bin, where 'x' is the drive on which you have
+installed the cygwin distribution.  Rebooting is also suggested if you
+are unable to find another cygwin DLL.
+To disable the usage of a unique key value of a certain Cygwin DLL, use
+the <command>cygcheck --disable-unique-object-names Cygwin-DLL</command>
+command.  <literal>Cygwin-DLL</literal> is the Windows path (*not* a 
+Cygwin POSIX path) to the DLL for which you want to disable this feature.
+Note that you have to stop all Cygwin processes running under this DLL,
+before you're allowed to change this setting.  For instance, run
+<command>cygcheck</command> from a DOS command line for this purpose.</para>
+<para>To re-enable the usage of a unique key, use the
+<command>cygcheck --enable-unique-object-names Cygwin-DLL</command> command.
+This option has the same characteristics as the
+<literal>--disable-unique-object-names</literal> option</para>
+<para>Last but not least, you can use
+<command>cygcheck --show-unique-object-names Cygwin-DLL</command> to find out
+if the given Cygwin DLL use unique object names or not.  In contrast to the
+<literal>--disable-...</literal> and <literal>--enable-...</literal> options,
+the <literal>--show-unique-object-names</literal> option also works for
+Cygwin DLLs which are currently in use.</para>
 <sect2 id="cygpath"><title>cygpath</title>

Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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