2022-01-21 16:44:13 +01:00
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2024-01-09 22:37:00 +01:00
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<TITLE>Magic-8.3 Command Reference</TITLE>
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2022-01-21 16:44:13 +01:00
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<BODY BACKGROUND=graphics/blpaper.gif>
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2024-01-09 22:37:00 +01:00
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<H1> <IMG SRC=graphics/magic_title8_3.png ALT="Magic VLSI Layout Tool Version 8.3">
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2022-01-21 16:44:13 +01:00
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<IMG SRC=graphics/magic_OGL_sm.gif ALIGN="top" ALT="*"> </H1>
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<H2>locking</H2>
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<HR>
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Control the behavior of file locking.
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<HR>
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<H3>Usage:</H3>
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<BLOCKQUOTE>
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<B>locking</B> [<B>enable</B>|<B>disable</B>] <BR><BR>
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</BLOCKQUOTE>
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<H3>Summary:</H3>
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<BLOCKQUOTE>
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The <B>locking</B> command controls the behavior of file locking,
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which is an operating system-level protocol for preventing multiple
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processes from attempting to write to the same file at the same
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time. The behavior of the protocol is operating system dependent;
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for Linux/UNIX systems, this is a feature of the system fcntl()
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call. When a file is opened, the file descriptor is associated
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with an exclusive lock that prevents any other process from opening
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the same file for writing or appending. When using the file locking
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feature, two processes of magic cannot open the same file in read/write
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mode. The first process to open the file will have the exclusive
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right to alter the file contents. The second process may only view
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the layout in read-only mode. <P>
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Any cell that is read-only can be forced editable using the
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"<B>cellname writeable</B>" command option. Note that this does
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not make the file writeable if another process has obtained a lock
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on the file; it merely makes it editable, but to save the modified
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layout to disk would require that the name of the cell be changed
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or that the process holding the file lock releases it. <P>
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This is not a perfect protection mechanism, since the "<B>cellname
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writeable</B>" command option can subvert the intent of the file
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lock by allowing a cell to be read in read-only mode while another
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process has it locked; then, after the other process has released
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the lock, the file can be forced writeable and saved to the same
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file, potentially overwriting modifications made by the other
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process. In normal use cases, however, the file locking serves
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to prevent unintended overwriting of file modifications. <P>
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The file locking is enabled by default when magic starts up.
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Generally speaking, there is no reason to disable it. However,
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some operating systems have strict limits on the allowed number
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of open file descriptors, and it is possible for a sufficiently
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complex layout for there to be more files open than available
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file descriptors. In that case, the <B>locking disable</B>
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command option will prevent issues with the filesystem at the
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expense of file lock protection. <P>
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With no arguments, <B>locking</B> returns the state of the
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file locking, either "<B>enabled</B>" or "<B>disabled</B>". <P>
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</BLOCKQUOTE>
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<H3>Implementation Notes:</H3>
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<BLOCKQUOTE>
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<B>locking</B> is implemented as a built-in command in <B>magic</B>
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from version tag 8.3.249.
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</BLOCKQUOTE>
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<H3>See Also:</H3>
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<BLOCKQUOTE>
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<A HREF=cellname.html><B>cellname</B></A> <BR>
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</BLOCKQUOTE>
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<P><IMG SRC=graphics/line1.gif><P>
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<TABLE BORDER=0>
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<TR>
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<TD> <A HREF=commands.html>Return to command index</A>
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</TR>
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</TABLE>
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<P><I>Last updated:</I> January 1, 2022 at 3:11pm <P>
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