Read/WriteOnePNGImage has a global lock which affects multithreading efficiency

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Hi All,

We are using GraphicsMagick-1.3.21 version to do image processing. We found
our program not picking up CPU usage even when load is high, and requests
just keep piling up.

We noticed that there is a png_semaphore in coders/png.c. And it serializes
ReadOnePNGImage and WriteOnePNGImage calls in our multithreading
environment. Which basically becomes the bottleneck of our program.

I noticed that this lock is just for setjmp/longjmp to handle exceptions,
and these calls are tricky and not necessarily thread-safe. Is there a way
to get around with that?

Thank you in advance!

Best,
Yuhan

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<div dir=3D"ltr"><div>Hi All,</div><div><br></div>We are using=C2=A0Graphic=
sMagick-1.3.21 version to do image processing. We found our program not pic=
king up CPU usage even when load is high, and requests just keep piling up.=
<div><br></div><div>We noticed that there is a png_semaphore in coders/png.=
c. And it serializes ReadOnePNGImage and WriteOnePNGImage calls in our mult=
ithreading environment. Which basically becomes the bottleneck of our progr=
am.</div><div><br></div><div>I noticed that this lock is just for setjmp/lo=
ngjmp to handle exceptions, and these calls are tricky and not necessarily =
thread-safe. Is there a way to get around with that?</div><div><br></div><d=
iv>Thank you in advance!</div><div><br></div><div>Best,</div><div>Yuhan</di=
v></div>

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