diff options
Diffstat (limited to 'libio/genops.c')
| -rw-r--r-- | libio/genops.c | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/libio/genops.c b/libio/genops.c index a466cfa337..6ad7346cae 100644 --- a/libio/genops.c +++ b/libio/genops.c @@ -570,11 +570,39 @@ _IO_init (_IO_FILE *fp, int flags) _IO_init_internal (fp, flags); } +static int stdio_needs_locking; + +/* In a single-threaded process most stdio locks can be omitted. After + _IO_enable_locks is called, locks are not optimized away any more. + It must be first called while the process is still single-threaded. + + This lock optimization can be disabled on a per-file basis by setting + _IO_FLAGS2_NEED_LOCK, because a file can have user-defined callbacks + or can be locked with flockfile and then a thread may be created + between a lock and unlock, so omitting the lock is not valid. + + Here we have to make sure that the flag is set on all existing files + and files created later. */ +void +_IO_enable_locks (void) +{ + _IO_ITER i; + + if (stdio_needs_locking) + return; + stdio_needs_locking = 1; + for (i = _IO_iter_begin (); i != _IO_iter_end (); i = _IO_iter_next (i)) + _IO_iter_file (i)->_flags2 |= _IO_FLAGS2_NEED_LOCK; +} +libc_hidden_def (_IO_enable_locks) + void _IO_old_init (_IO_FILE *fp, int flags) { fp->_flags = _IO_MAGIC|flags; fp->_flags2 = 0; + if (stdio_needs_locking) + fp->_flags2 |= _IO_FLAGS2_NEED_LOCK; fp->_IO_buf_base = NULL; fp->_IO_buf_end = NULL; fp->_IO_read_base = NULL; |