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authorJoseph Blomstedt <joe@basho.com>2012-11-29 14:50:42 -0800
committerSteve Vinoski <vinoski@ieee.org>2013-11-15 10:19:19 -0500
commitf47c818746c1df4055b1de8aabf47364f502274c (patch)
treea85d3ba3585a4bf29d01c3d6a7d43f0b75bab9f4 /lib/kernel/doc/src
parentc01df2215ac3ddef82116abac5eaf236d3788f21 (diff)
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Add sync option to file:open/2
The sync option adds the POSIX O_SYNC flag to the open system call on platforms that support the flag or its equivalent, e.g., FILE_FLAG_WRITE_THROUGH on Windows. For platforms that don't support it, file:open/2 returns {error, enotsup} if the sync option is passed in. The semantics of O_SYNC are platform-specific. For example, not all platforms guarantee that all file metadata are written to the disk along with the file data when the flag is in effect. This issue is noted in the documentation this commit adds for the sync option. Add a test for the sync option. Note however that the underlying OS semantics for O_SYNC can't be tested automatically in any practical way, so the test assumes the OS does the right thing with the flag when present. For manual verification, dtruss on OS X and strace on Linux were both run against beam processes to watch calls to open(), and file:open/2 was called in Erlang shells to open files for writing, both with and without the sync option. Both the dtruss output and the strace output showed that the O_SYNC flag was present in the open() calls when sync was specified and was clear when sync was not specified.
Diffstat (limited to 'lib/kernel/doc/src')
-rw-r--r--lib/kernel/doc/src/file.xml10
1 files changed, 10 insertions, 0 deletions
diff --git a/lib/kernel/doc/src/file.xml b/lib/kernel/doc/src/file.xml
index 66ecba1bf2..420ecbc3a6 100644
--- a/lib/kernel/doc/src/file.xml
+++ b/lib/kernel/doc/src/file.xml
@@ -826,6 +826,16 @@
<item>
<p><c>File</c> must be <c>iodata()</c>. Returns an <c>fd()</c> which lets the <c>file</c> module operate on the data in-memory as if it is a file.</p>
</item>
+ <tag><c>sync</c></tag>
+ <item>
+ <p>On platforms that support it, enables the POSIX <c>O_SYNC</c> synchronous I/O flag or its platform-dependent
+ equivalent (e.g., <c>FILE_FLAG_WRITE_THROUGH</c> on Windows) so that writes to the file block until the data has
+ been physically written to disk. Be aware, though, that the exact semantics of this flag differ from platform to
+ platform; for example, neither Linux nor Windows guarantees that all file metadata are also written before the call
+ returns. For precise semantics, check the details of your platform's documentation. On platforms with no
+ support for POSIX <c>O_SYNC</c> or equivalent, use of the <c>sync</c> flag causes <c>open</c> to return
+ <c>{error, enotsup}</c>.</p>
+ </item>
</taglist>
<p>Returns:</p>
<taglist>