• Andreas Rheinhardt's avatar
    avcodec/fft_template, fft_init_table: Make ff_fft_init() thread-safe · b9c1ab89
    Andreas Rheinhardt authored
    Commit 1af61568 put initializing
    the ff_fft_offsets_lut (which is typically used if FFT_FIXED_32)
    behind an ff_thread_once() to make ff_fft_init() thread-safe; yet
    there is a second place where said table may be initialized which
    is not guarded by this AVOnce: ff_fft_init_mips(). MIPS uses this LUT
    even for ordinary floating point FFTs, so that ff_fft_init() is not
    thread-safe (on MIPS) for both 32bit fixed-point as well as
    floating-point FFTs; e.g. ff_mdct_init() inherits this flaw and
    therefore initializing e.g. the AAC decoders is not thread-safe (on
    MIPS) despite them having FF_CODEC_CAP_INIT_CLEANUP set.
    
    This commit fixes this by moving the AVOnce to fft_init_table.c and
    using it to guard all initializations of ff_fft_offsets_lut.
    
    (It is not that bad in practice, because every entry of
    ff_fft_offsets_lut is never read during initialization and is only once
    ever written to (namely to its final value); but even these are
    conflicting actions which are (by definition) data races and lead to
    undefined behaviour.)
    Signed-off-by: 's avatarAndreas Rheinhardt <andreas.rheinhardt@gmail.com>
    b9c1ab89
fft_init_table.c 26.6 KB