fio: Fix race condition in fio.read

When fio.read  from multiple fibers is performed, as fio.read yields before
performing actual read operation and ibuf shared among several fibers
may be corrupted and read data is mixed.

The fix is to create new ibuf for each fio.read call in case
buffer is not specified.

Closes #3187

src/lua/fio.lua

@@ -40,8 +40,7 @@ fio_methods.read = function(self, buf, size)
     end
     if not ffi.istype(const_char_ptr_t, buf) then
         size = buf or size
-        tmpbuf = buffer.IBUF_SHARED
-        tmpbuf:reset()
+        tmpbuf = buffer.ibuf()
         buf = tmpbuf:reserve(size)
     end
     local res, err = internal.read(self.fh, buf, size)

test/app/fio.result

@@ -1067,6 +1067,76 @@ fio.unlink(tmpfile)
 ---
 - true
 ...
+tmp1 = fio.pathjoin(tmpdir, "tmp1")
+---
+...
+tmp2= fio.pathjoin(tmpdir, "tmp2")
+---
+...
+test_run:cmd("setopt delimiter ';'")
+---
+- true
+...
+function write_file(name, odd)
+    local fh = fio.open(name, { 'O_RDWR', 'O_TRUNC', 'O_CREAT' }, 0777)
+    if odd then
+        fh:write(string.rep('1', 100))
+    else
+        fh:write(string.rep('2', 100))
+    end
+    fh:write(name)
+    fh:seek(0)
+    return fh
+end;
+---
+...
+test_run:cmd("setopt delimiter ''");
+---
+- true
+...
+fh1 = write_file(tmp1)
+---
+...
+fh2 = write_file(tmp2)
+---
+...
+fiber = require('fiber')
+---
+...
+digest = require('digest')
+---
+...
+str = fh1:read()
+---
+...
+fh1:seek(0)
+---
+- 0
+...
+hash = digest.crc32(str)
+---
+...
+ch = fiber.channel(1)
+---
+...
+f1 = fiber.create(function() str = fh1:read() ch:put(digest.crc32(str)) end)
+---
+...
+f2 = fiber.create(function() str = fh2:read() end)
+---
+...
+ch:get() == hash
+---
+- true
+...
+fio.unlink(tmp1)
+---
+- true
+...
+fio.unlink(tmp2)
+---
+- true
+...
 fio.rmdir(tmpdir)
 ---
 - true

test/app/fio.test.lua

@@ -342,4 +342,33 @@ fio.path.lexists(link)
 
 fio.unlink(link)
 fio.unlink(tmpfile)
+tmp1 = fio.pathjoin(tmpdir, "tmp1")
+tmp2= fio.pathjoin(tmpdir, "tmp2")
+test_run:cmd("setopt delimiter ';'")
+function write_file(name, odd)
+    local fh = fio.open(name, { 'O_RDWR', 'O_TRUNC', 'O_CREAT' }, 0777)
+    if odd then
+        fh:write(string.rep('1', 100))
+    else
+        fh:write(string.rep('2', 100))
+    end
+    fh:write(name)
+    fh:seek(0)
+    return fh
+end;
+test_run:cmd("setopt delimiter ''");
+fh1 = write_file(tmp1)
+fh2 = write_file(tmp2)
+fiber = require('fiber')
+digest = require('digest')
+str = fh1:read()
+fh1:seek(0)
+hash = digest.crc32(str)
+ch = fiber.channel(1)
+f1 = fiber.create(function() str = fh1:read() ch:put(digest.crc32(str)) end)
+f2 = fiber.create(function() str = fh2:read() end)
+ch:get() == hash
+
+fio.unlink(tmp1)
+fio.unlink(tmp2)
 fio.rmdir(tmpdir)