From 4bd026cccb2c22279dd9c88e704642c5a65d3c53 Mon Sep 17 00:00:00 2001 From: Michael Santos Date: Fri, 30 Apr 2010 12:22:11 -0400 Subject: Support opening files in exclusive mode 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]). --- lib/kernel/doc/src/file.xml | 13 ++++++++++++- lib/kernel/src/file.erl | 2 +- lib/kernel/test/file_SUITE.erl | 20 ++++++++++++++++++-- lib/kernel/test/prim_file_SUITE.erl | 20 ++++++++++++++++++-- 4 files changed, 49 insertions(+), 6 deletions(-) (limited to 'lib') diff --git a/lib/kernel/doc/src/file.xml b/lib/kernel/doc/src/file.xml index 382262d1ee..a9ceac0bcf 100644 --- a/lib/kernel/doc/src/file.xml +++ b/lib/kernel/doc/src/file.xml @@ -603,7 +603,7 @@ f.txt: {person, "kalle", 25}. Filename = name() Modes = [Mode] -  Mode = read | write | append | raw | binary | {delayed_write, Size, Delay} | delayed_write | {read_ahead, Size} | read_ahead | compressed +  Mode = read | write | append | exclusive | raw | binary | {delayed_write, Size, Delay} | delayed_write | {read_ahead, Size} | read_ahead | compressed   Size = Delay = int() IoDevice = io_device() Reason = ext_posix() | system_limit @@ -630,6 +630,17 @@ f.txt: {person, "kalle", 25}. file opened with append will take place at the end of the file.

+ exclusive + +

The file, when opened for writing, is created if it + does not exist. If the file exists, open will return + {error, eexist}.

+

This option does not guarantee exclusiveness on + file systems that do not support O_EXCL properly, + such as NFS. Do not depend on this option unless you + know that the file system supports it (in general, local + file systems should be safe).

 + raw

The raw option allows faster access to a file, diff --git a/lib/kernel/src/file.erl b/lib/kernel/src/file.erl index a37614e424..1ba329a12b 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 15bab0dccd..17c47f871d 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, datasync/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]). @@ -466,7 +466,7 @@ files(suite) -> sync,datasync,advise]. 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) -> []; @@ -840,6 +840,22 @@ 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 21bdc06fdc..1688ec45ca 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, datasync/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, @@ -385,7 +385,7 @@ win_cur_dir_1(_Config, Handle) -> files(suite) -> [open,pos,file_info,truncate,sync,datasync,advise]. open(suite) -> [open1,modes,close,access,read_write, - pread_write,append]. + pread_write,append,exclusive]. open1(suite) -> []; open1(doc) -> []; @@ -610,6 +610,22 @@ 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]. -- cgit v1.2.3