The last two are identical; "atomic" is the default behavior (note that it is not actually a keyword; it is specified only by the absence of nonatomic
-- atomic
was added as a keyword in recent versions of llvm/clang).
Assuming that you are @synthesizing the method implementations, atomic vs. non-atomic changes the generated code. If you are writing your own setter/getters, atomic/nonatomic/retain/assign/copy are merely advisory. (Note: @synthesize is now the default behavior in recent versions of LLVM. There is also no need to declare instance variables; they will be synthesized automatically, too, and will have an _
prepended to their name to prevent accidental direct access).
With "atomic", the synthesized setter/getter will ensure that a whole value is always returned from the getter or set by the setter, regardless of setter activity on any other thread. That is, if thread A is in the middle of the getter while thread B calls the setter, an actual viable value -- an autoreleased object, most likely -- will be returned to the caller in A.
In nonatomic
, no such guarantees are made. Thus, nonatomic
is considerably faster than "atomic".
What "atomic" does not do is make any guarantees about thread safety. If thread A is calling the getter simultaneously with thread B and C calling the setter with different values, thread A may get any one of the three values returned -- the one prior to any setters being called or either of the values passed into the setters in B and C. Likewise, the object may end up with the value from B or C, no way to tell.
Ensuring data integrity -- one of the primary challenges of multi-threaded programming -- is achieved by other means.
Adding to this:
atomicity
of a single property also cannot guarantee thread safety when multiple dependent properties are in play.
Consider:
@property(atomic, copy) NSString *firstName;
@property(atomic, copy) NSString *lastName;
@property(readonly, atomic, copy) NSString *fullName;
In this case, thread A could be renaming the object by calling setFirstName:
and then calling setLastName:
. In the meantime, thread B may call fullName
in between thread A's two calls and will receive the new first name coupled with the old last name.
To address this, you need a transactional model. I.e. some other kind of synchronization and/or exclusion that allows one to exclude access to fullName
while the dependent properties are being updated.
Example for PAT/PMT initalization length 560
starting at offset 0
in main.mp4
#EXTM3U
#EXT-X-TARGETDURATION:5
#EXT-X-VERSION:7
#EXT-X-MEDIA-SEQUENCE:1
#EXT-X-PLAYLIST-TYPE:VOD
#EXT-X-KEY:METHOD=AES-128,URI="./slow_loading.php?delay=5&resource=crypt0.key",IV=0xbf9840dc7d7fa163301a6c38844d6239
#EXT-X-MAP:URI="main.mp4",BYTERANGE="560@0"
#EXTINF:4.96907,
#EXT-X-BYTERANGE:25312@560
main.mp4
#EXTINF:4.96907,
#EXT-X-BYTERANGE:25440@25872
main.mp4
#EXTINF:4.96907,
#EXT-X-BYTERANGE:25440@51312
main.mp4
#EXTINF:4.96907,
#EXT-X-BYTERANGE:25440@76752
main.mp4
...
Source
Best Answer
Short answer: No.
Wether Live or VOD,
EXT-X-TARGETDURATION
specifies a maximum duration for the segments in the playlist. The actual duration specified byEXTINF
may be less. In the HLS draft [1] it says:The way I read the error
is that the
EXTINF
for the particular segment with sequence number 477000, 477000.ts that is, was 8.000000 in the previous playlist and is 6.000000 in the playlist just switched to. AFAIK there is no regulation that demands for those durations to be equal. Maybe the player cannot handle this for some reason.You can test your HLS stream for conformance using Apple's MediaStreamValidator [2] command-line tool. It will show any issues that the stream might have.
[1] https://datatracker.ietf.org/doc/html/draft-pantos-http-live-streaming-19#section-4.3.3.1
[2] https://developer.apple.com/library/ios/technotes/tn2235/_index.html