Calling from C to Java is very slow. In the worst case, when no
method block is provided, the calling sequence can (I think) acquire and
release as many as 8+ locks, even if the called method is not even
synchronized. This should also have an impact on salability.

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There seems to be some question how often this acutally happens, so I asked around and found that JavaMedia does this a lot. Here is one comment:

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java sound uses callbacks from native code to java pretty
aggressively. it calls back as often as once ever 11
milliseconds for each audio stream being rendered. (we
also have a few much less frequently made callbacks to
signal that audio playback has started or finished, etc.)
since jmf uses java sound for its audio support, this will
affect the performance of jmf as well as java sound on its
own.
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We also found that non-sound related parts of JMF do this often.
steve.wilson@eng 1999-01-08