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< Erlang patches mailing list ~ [PATCH] Support opening files in exclusive mode

Guest

Posted: Fri Apr 30, 2010 4:22 pm

Guest

Add an option that atomically tests for the existence of a file and
creates it if the file does not exist, by passing the O_EXCL flag
to open() on Unix and CREATE_NEW flag on Windows. Support for O_EXCL
varies across platforms and filesystems.

{ok, Fd} = file:open("/tmp/foo", [write,exclusive]),
{error, eexist} = file:open("/tmp/foo", [write,exclusive]).
---
erts/emulator/drivers/common/erl_efile.h | 3 ++-
erts/emulator/drivers/unix/unix_efile.c | 3 +++
erts/emulator/drivers/win32/win_efile.c | 3 +++
erts/preloaded/src/prim_file.erl | 5 ++++-
lib/kernel/doc/src/file.xml | 8 +++++++-
lib/kernel/src/file.erl | 2 +-
lib/kernel/test/file_SUITE.erl | 20 ++++++++++++++++++--
lib/kernel/test/prim_file_SUITE.erl | 20 ++++++++++++++++++--
8 files changed, 56 insertions(+), 8 deletions(-)

diff --git a/erts/emulator/drivers/common/erl_efile.h b/erts/emulator/drivers/common/erl_efile.h
index 9aa941e..d2ef9c0 100644
--- a/erts/emulator/drivers/common/erl_efile.h
+++ b/erts/emulator/drivers/common/erl_efile.h
@@ -32,7 +32,8 @@
#define EFILE_MODE_READ_WRITE 3
#define EFILE_MODE_APPEND 4
#define EFILE_COMPRESSED 8
-#define EFILE_NO_TRUNCATE 16 /* Special for reopening on VxWorks */
+#define EFILE_MODE_EXCL 16
+#define EFILE_NO_TRUNCATE 32 /* Special for reopening on VxWorks */

/*
* Seek modes for efile_seek().
diff --git a/erts/emulator/drivers/unix/unix_efile.c b/erts/emulator/drivers/unix/unix_efile.c
index d395b68..6171272 100644
--- a/erts/emulator/drivers/unix/unix_efile.c
+++ b/erts/emulator/drivers/unix/unix_efile.c
@@ -751,6 +751,9 @@ efile_openfile(Efile_error* errInfo, /* Where to return error codes. */
#endif
}

+ if (flags & EFILE_MODE_EXCL) {
+ mode |= O_EXCL;
+ }

#ifdef VXWORKS
if (*name != '/') {
diff --git a/erts/emulator/drivers/win32/win_efile.c b/erts/emulator/drivers/win32/win_efile.c
index 89aaad3..de5cd21 100644
--- a/erts/emulator/drivers/win32/win_efile.c
+++ b/erts/emulator/drivers/win32/win_efile.c
@@ -689,6 +689,9 @@ Sint64* pSize; /* Where to store the size of the file. */
if (flags & EFILE_MODE_APPEND) {
crFlags = OPEN_ALWAYS;
}
+ if (flags & EFILE_MODE_EXCL) {
+ crFlags = CREATE_NEW;
+ }
fd = CreateFile(name, access, FILE_SHARE_READ | FILE_SHARE_WRITE,
NULL, crFlags, FILE_ATTRIBUTE_NORMAL, NULL);

diff --git a/erts/preloaded/src/prim_file.erl b/erts/preloaded/src/prim_file.erl
index 43e6f6c..035ff3e 100644
--- a/erts/preloaded/src/prim_file.erl
+++ b/erts/preloaded/src/prim_file.erl
@@ -114,9 +114,10 @@
-define(EFILE_MODE_READ_WRITE, 3).
-define(EFILE_MODE_APPEND, 4).
-define(EFILE_COMPRESSED, Cool

.
+-define(EFILE_MODE_EXCL, 16).

%% Use this mask to get just the mode bits to be passed to the driver.
--define(EFILE_MODE_MASK, 15).
+-define(EFILE_MODE_MASK, 31).

%% Seek modes for the driver's seek function.
-define(EFILE_SEEK_SET, 0).
@@ -918,6 +919,8 @@ open_mode([compressed|Rest], Mode, Portopts, Setopts) ->
open_mode([append|Rest], Mode, Portopts, Setopts) ->
open_mode(Rest, Mode bor ?EFILE_MODE_APPEND bor ?EFILE_MODE_WRITE,
Portopts, Setopts);
+open_mode([exclusive|Rest], Mode, Portopts, Setopts) ->
+ open_mode(Rest, Mode bor ?EFILE_MODE_EXCL, Portopts, Setopts);
open_mode([delayed_write|Rest], Mode, Portopts, Setopts) ->
open_mode([{delayed_write, 64*1024, 2000}|Rest], Mode,
Portopts, Setopts);
diff --git a/lib/kernel/doc/src/file.xml b/lib/kernel/doc/src/file.xml
index 50f9722..eed92d2 100644
--- a/lib/kernel/doc/src/file.xml
+++ b/lib/kernel/doc/src/file.xml
@@ -584,7 +584,7 @@ f.txt: {person, "kalle", 25}.
<type>
<v>Filename = name()</v>
<v>Modes = [Mode]</v>
- <v> Mode = read | write | append | raw | binary | {delayed_write, Size, Delay} | delayed_write | {read_ahead, Size} | read_ahead | compressed</v>
+ <v> Mode = read | write | append | exclusive | raw | binary | {delayed_write, Size, Delay} | delayed_write | {read_ahead, Size} | read_ahead | compressed</v>
<v>  Size = Delay = int()</v>
<v>IoDevice = io_device()</v>
<v>Reason = ext_posix() | system_limit</v>
@@ -611,6 +611,12 @@ f.txt: {person, "kalle", 25}.
file opened with <c>append</c> will take place at
the end of the file.</p>
</item>
+ <tag><c>exclusive</c></tag>
+ <item>
+ <p>The file, when opened for writing, is created if it
+ does not exist. If the file exists, open will return
+ <c>{error, eexist}</c>.</p>
+ </item>
<tag><c>raw</c></tag>
<item>
<p>The <c>raw</c> option allows faster access to a file,
diff --git a/lib/kernel/src/file.erl b/lib/kernel/src/file.erl
index 46ffa9d..419d8db 100644
--- a/lib/kernel/src/file.erl
+++ b/lib/kernel/src/file.erl
@@ -81,7 +81,7 @@
-type mode() :: 'read' | 'write' | 'append' | 'raw' | 'binary' |
{'delayed_write', non_neg_integer(), non_neg_integer()} |
'delayed_write' | {'read_ahead', pos_integer()} |
- 'read_ahead' | 'compressed'.
+ 'read_ahead' | 'compressed' | 'exclusive'.
-type name() :: string() | atom() | [name()].
-type posix() :: atom().
-type bindings() :: any().
diff --git a/lib/kernel/test/file_SUITE.erl b/lib/kernel/test/file_SUITE.erl
index d01e1f1..b9d57ce 100644
--- a/lib/kernel/test/file_SUITE.erl
+++ b/lib/kernel/test/file_SUITE.erl
@@ -53,7 +53,7 @@
-export([file_info/1, file_info_basic_file/1, file_info_basic_directory/1,
file_info_bad/1, file_info_times/1, file_write_file_info/1]).
-export([rename/1, access/1, truncate/1, sync/1,
- read_write/1, pread_write/1, append/1]).
+ read_write/1, pread_write/1, append/1, exclusive/1]).
-export([errors/1, e_delete/1, e_rename/1, e_make_dir/1, e_del_dir/1]).
-export([otp_5814/1]).

@@ -377,7 +377,7 @@ win_cur_dir_1(_Config) ->
files(suite) -> [open,pos,file_info,consult,eval,script,truncate,sync].

open(suite) -> [open1,old_modes,new_modes,path_open,close,access,read_write,
- pread_write,append,open_errors].
+ pread_write,append,open_errors,exclusive].

open1(suite) -> [];
open1(doc) -> [];
@@ -751,6 +751,22 @@ open_errors(Config) when is_list(Config) ->
?line test_server:timetrap_cancel(Dog),
ok.

+exclusive(suite) -> [];
+exclusive(doc) -> "Test exclusive access to a file.";
+exclusive(Config) when is_list(Config) ->
+ ?line Dog = test_server:timetrap(test_server:seconds(5)),
+ ?line RootDir = ?config(priv_dir,Config),
+ ?line NewDir = filename:join(RootDir,
+ atom_to_list(?MODULE)
+ ++"_exclusive"),
+ ?line ok = ?FILE_MODULE:make_dir(NewDir),
+ ?line Name = filename:join(NewDir, "ex_file.txt"),
+ ?line {ok, Fd} = ?FILE_MODULE:open(Name, [write, exclusive]),
+ ?line {error, eexist} = ?FILE_MODULE:open(Name, [write, exclusive]),
+ ?line ok = ?FILE_MODULE:close(Fd),
+ ?line test_server:timetrap_cancel(Dog),
+ ok.
+
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

pos(suite) -> [pos1,pos2].
diff --git a/lib/kernel/test/prim_file_SUITE.erl b/lib/kernel/test/prim_file_SUITE.erl
index 860aeec..9f6dd78 100644
--- a/lib/kernel/test/prim_file_SUITE.erl
+++ b/lib/kernel/test/prim_file_SUITE.erl
@@ -35,7 +35,7 @@
file_write_file_info_a/1, file_write_file_info_b/1]).
-export([rename_a/1, rename_b/1,
access/1, truncate/1, sync/1,
- read_write/1, pread_write/1, append/1]).
+ read_write/1, pread_write/1, append/1, exclusive/1]).
-export([errors/1, e_delete/1, e_rename/1, e_make_dir/1, e_del_dir/1]).

-export([compression/1, read_not_really_compressed/1,
@@ -380,7 +380,7 @@ win_cur_dir_1(_Config, Handle) ->
files(suite) -> [open,pos,file_info,truncate,sync].

open(suite) -> [open1,modes,close,access,read_write,
- pread_write,append].
+ pread_write,append,exclusive].

open1(suite) -> [];
open1(doc) -> [];
@@ -605,6 +605,22 @@ append(Config) when is_list(Config) ->
?line test_server:timetrap_cancel(Dog),
ok.

+exclusive(suite) -> [];
+exclusive(doc) -> "Test exclusive access to a file.";
+exclusive(Config) when is_list(Config) ->
+ ?line Dog = test_server:timetrap(test_server:seconds(5)),
+ ?line RootDir = ?config(priv_dir,Config),
+ ?line NewDir = filename:join(RootDir,
+ atom_to_list(?MODULE)
+ ++"_exclusive"),
+ ?line ok = ?PRIM_FILE:make_dir(NewDir),
+ ?line Name = filename:join(NewDir, "ex_file.txt"),
+ ?line {ok,Fd} = ?PRIM_FILE:open(Name, [write, exclusive]),
+ ?line {error, eexist} = ?PRIM_FILE:open(Name, [write, exclusive]),
+ ?line ok = ?PRIM_FILE:close(Fd),
+ ?line test_server:timetrap_cancel(Dog),
+ ok.
+
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

pos(suite) -> [pos1,pos2].
--
1.5.6.4

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Guest

Posted: Fri Apr 30, 2010 4:22 pm

Guest

Posted: Mon May 03, 2010 5:42 am

Guest

On Fri, Apr 30, 2010 at 6:22 PM, Michael Santos
<michael.santos@gmail.com> wrote:
> Add an option that atomically tests for the existence of a file and
> creates it if the file does not exist, by passing the O_EXCL flag
> to open() on Unix and CREATE_NEW flag on Windows. Support for O_EXCL
> varies across platforms and filesystems.
>
> {ok, Fd} = file:open("/tmp/foo", [write,exclusive]),
> {error, eexist} = file:open("/tmp/foo", [write,exclusive]).

Thanks! Will include in 'pu'.

--
Björn Gustavsson, Erlang/OTP, Ericsson AB

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erlang-patches (at) erlang.org mailing list.
See http://www.erlang.org/faq.html
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Guest

Posted: Mon May 03, 2010 5:42 am

Guest

All times are GMT

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< Erlang patches mailing list ~ [PATCH] Support opening files in exclusive mode