[Tarantool-patches] [PATCH 1/1] fio: close unused descriptors automatically

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

Fio.open() returned a file descriptor, which was not closed
automatically after all its links were nullified. In other words,
GC didn't close the descriptor.

This was not really useful, because after fio.open() an exception
may appear, and user needed to workaround this to manually call
fio_object:close(). Also this was not consistent with io.open().

Now fio.open() object closes the descriptor automatically when
GCed.

Closes #4727

@TarantoolBot document
Title: fio descriptor is closed automatically by GC

fio.open() returns a descriptor which can be closed manually by
calling :close() method, or it will be closed automatically, when
it has no references, and GC deletes it.

:close() method existed always, auto GC was added just now.
---

@ChangeLog
- fio descriptors are closed on garbage collection (gh-4727).

 src/lua/fio.lua       | 33 ++++++++++++---
 test/app/fio.result   | 93 +++++++++++++++++++++++++++++++++++++++++++
 test/app/fio.test.lua | 58 +++++++++++++++++++++++++++
 3 files changed, 178 insertions(+), 6 deletions(-)

diff --git a/src/lua/fio.lua b/src/lua/fio.lua
index 4692e1026..41901904c 100644
--- a/src/lua/fio.lua
+++ b/src/lua/fio.lua
@@ -141,10 +141,12 @@ end
 
 fio_methods.close = function(self)
     local res, err = internal.close(self.fh)
-    self.fh = -1
     if err ~= nil then
         return false, err
     end
+    ffi.gc(self._gc, nil)
+    self._gc = nil
+    self.fh = -1
     return res
 end
 
@@ -160,7 +162,23 @@ fio_methods.stat = function(self)
     return internal.fstat(self.fh)
 end
 
-local fio_mt = { __index = fio_methods }
+local fio_mt = {
+    __index = fio_methods,
+    __serialize = function(obj)
+        return {fh = obj.fh}
+    end,
+}
+
+local function fio_wrap(fh)
+    return setmetatable({
+        fh = fh,
+        _gc = ffi.gc(ffi.new('char[1]'), function()
+            -- FFI GC can't yield. Internal.close() yields.
+            -- Collect the garbage later, in a separate fiber.
+            fiber.create(internal.close, fh)
+        end)
+    }, fio_mt)
+end
 
 fio.open = function(path, flags, mode)
     local iflag = 0
@@ -202,10 +220,13 @@ fio.open = function(path, flags, mode)
     if err ~= nil then
         return nil, err
     end
-
-    fh = { fh = fh }
-    setmetatable(fh, fio_mt)
-    return fh
+    local ok, res = pcall(fio_wrap, fh)
+    if not ok then
+        internal.close(fh)
+        -- This is either OOM or bad syntax, both require throw.
+        return error(res)
+    end
+    return res
 end
 
 fio.pathjoin = function(...)
diff --git a/test/app/fio.result b/test/app/fio.result
index f83c43f44..6345ac22e 100644
--- a/test/app/fio.result
+++ b/test/app/fio.result
@@ -1456,3 +1456,96 @@ fio.mktree('/dev/null/dir')
 - false
 - 'Error creating directory /dev/null: File exists'
 ...
+--
+-- gh-4727: fio handler GC.
+--
+flags = {'O_CREAT', 'O_RDWR'}
+---
+...
+mode = {'S_IRWXU'}
+---
+...
+filename = 'test4727.txt'
+---
+...
+fh1 = nil
+---
+...
+fh2 = nil
+---
+...
+-- Idea of the test is that according to the Open Group standard,
+-- open() always returns the smallest available descriptor. This
+-- means, that in 'open() + close() + open()' the second open()
+-- should return the same value as the first call, if no other
+-- threads/fibers managed to interfere. Because of the
+-- interference the sequence may need to be called multiple times
+-- to catch a couple of equal descriptors.
+-- GC function of a fio object creates a new fiber. Give it         \
+-- time to execute.                                                 \
+test_run:wait_cond(function()                                       \
+    collectgarbage('collect')                                       \
+    local f = fio.open(filename, flags, mode)                       \
+    fh1 = f.fh                                                      \
+    f = nil                                                         \
+    collectgarbage('collect')                                       \
+    fiber.yield()                                                   \
+    f = fio.open(filename, flags, mode)                             \
+    fh2 = f.fh                                                      \
+    f = nil                                                         \
+    collectgarbage('collect')                                       \
+    fiber.yield()                                                   \
+    return fh1 == fh2                                               \
+end) or {fh1, fh2}
+---
+- true
+...
+-- Ensure, that GC does not break anything after explicit close.
+-- Idea of the test is the same as in the previous test, but now
+-- the second descriptor is used for something. If GC of the first
+-- fio object is called even after close(), it would close the
+-- same descriptor, already used by the second fio object. And it
+-- won't be able to write anything. Or will write, but to a
+-- totally different descriptor created by some other
+-- fiber/thread. This is why read() is called on the same file
+-- afterwards.
+f = nil
+---
+...
+test_run:wait_cond(function()                                       \
+    f = fio.open(filename, flags, mode)                             \
+    fh1 = f.fh                                                      \
+    f:close()                                                       \
+    f = fio.open(filename, flags, mode)                             \
+    fh2 = f.fh                                                      \
+    return fh1 == fh2                                               \
+end)
+---
+- true
+...
+collectgarbage('collect')
+---
+- 0
+...
+fiber.yield()
+---
+...
+f:write('test')
+---
+- true
+...
+f:close()
+---
+- true
+...
+f = fio.open(filename, flags, mode)
+---
+...
+f:read()
+---
+- test
+...
+f:close()
+---
+- true
+...
diff --git a/test/app/fio.test.lua b/test/app/fio.test.lua
index 56c957d8a..c726bade6 100644
--- a/test/app/fio.test.lua
+++ b/test/app/fio.test.lua
@@ -474,3 +474,61 @@ test_run:cmd("clear filter")
 --
 fio.mktree('/dev/null')
 fio.mktree('/dev/null/dir')
+
+--
+-- gh-4727: fio handler GC.
+--
+flags = {'O_CREAT', 'O_RDWR'}
+mode = {'S_IRWXU'}
+filename = 'test4727.txt'
+fh1 = nil
+fh2 = nil
+-- Idea of the test is that according to the Open Group standard,
+-- open() always returns the smallest available descriptor. This
+-- means, that in 'open() + close() + open()' the second open()
+-- should return the same value as the first call, if no other
+-- threads/fibers managed to interfere. Because of the
+-- interference the sequence may need to be called multiple times
+-- to catch a couple of equal descriptors.
+test_run:wait_cond(function()                                       \
+    collectgarbage('collect')                                       \
+    local f = fio.open(filename, flags, mode)                       \
+    fh1 = f.fh                                                      \
+    f = nil                                                         \
+    collectgarbage('collect')                                       \
+-- GC function of a fio object creates a new fiber. Give it         \
+-- time to execute.                                                 \
+    fiber.yield()                                                   \
+    f = fio.open(filename, flags, mode)                             \
+    fh2 = f.fh                                                      \
+    f = nil                                                         \
+    collectgarbage('collect')                                       \
+    fiber.yield()                                                   \
+    return fh1 == fh2                                               \
+end) or {fh1, fh2}
+
+-- Ensure, that GC does not break anything after explicit close.
+-- Idea of the test is the same as in the previous test, but now
+-- the second descriptor is used for something. If GC of the first
+-- fio object is called even after close(), it would close the
+-- same descriptor, already used by the second fio object. And it
+-- won't be able to write anything. Or will write, but to a
+-- totally different descriptor created by some other
+-- fiber/thread. This is why read() is called on the same file
+-- afterwards.
+f = nil
+test_run:wait_cond(function()                                       \
+    f = fio.open(filename, flags, mode)                             \
+    fh1 = f.fh                                                      \
+    f:close()                                                       \
+    f = fio.open(filename, flags, mode)                             \
+    fh2 = f.fh                                                      \
+    return fh1 == fh2                                               \
+end)
+collectgarbage('collect')
+fiber.yield()
+f:write('test')
+f:close()
+f = fio.open(filename, flags, mode)
+f:read()
+f:close()
-- 
2.21.1 (Apple Git-122.3)