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PROTOTYPE WIP: Add thread-safe read functions to input files
The fact that OpenEXR read methods (readPixels, readTiles, etc.) all require a prior call to setFrameBuffer() prevents truly concurrent reads by multiple threads because the calling application needs to maintain a mutex that keeps any other threads from reading from the same file between the two function calls. This PR is aimed to implement a new set of API calls, variety of the readPixels et al. that take a `const FrameBuffer&` as parameter rather than relying on saved state, and thus allows truly concurrent reads by multiple threads -- if they use these new safe versions, obviously the old ones continue to be unsafe to use concurrently. It's a lot of work to do this right! And I'm not aiming to make it good right now, but only to minimally stake out the API and make it functional (even if inefficient) so that we are essentially "reserving" the API just in time for a 3.2 release, and then we can iterate on improving the implementation underneath in subsequent patches, without changing APIs or breaking ABI compatibility within the 3.2 family. At the moment, I'm just posting a subset of the work as a prototype so people can see where I'm going with it. I've implemented a simple design (just lock internally) for a couple classes. So I'm seeking feedback on which of the following options are preferred: 1. Flesh this out for ALL the classes and relevant methods ASAP in time for 3.2. 2. Since these are not virtual methods, adding them doesn't actually break the ABIs, so don't rush this, we can add them (all at once, or incrementally) in subsequent 3.2.x patch releases. 3. Just hold off on all of it until 3.3. Signed-off-by: Larry Gritz <[email protected]>
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‎src/lib/OpenEXR/ImfInputFile.cpp

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Original file line numberDiff line numberDiff line change
@@ -899,12 +899,43 @@ InputFile::readPixels (int scanLine1, int scanLine2)
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}
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}
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void
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InputFile::readPixels (const FrameBuffer& frameBuffer, int scanLine1, int scanLine2)
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{
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if (_data->compositor)
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{
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#if ILMTHREAD_THREADING_ENABLED
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std::lock_guard<std::mutex> lock (*_data);
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#endif
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setFrameBuffer (frameBuffer);
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_data->compositor->readPixels (scanLine1, scanLine2);
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}
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else if (_data->isTiled)
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{
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#if ILMTHREAD_THREADING_ENABLED
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std::lock_guard<std::mutex> lock (*_data);
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#endif
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setFrameBuffer (frameBuffer);
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bufferedReadPixels (_data, scanLine1, scanLine2);
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}
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else
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{
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_data->sFile->readPixels (frameBuffer, scanLine1, scanLine2);
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}
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}
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void
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InputFile::readPixels (int scanLine)
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{
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readPixels (scanLine, scanLine);
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}
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void
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InputFile::readPixels (const FrameBuffer& frameBuffer, int scanLine)
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{
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readPixels (frameBuffer, scanLine, scanLine);
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}
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void
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InputFile::rawPixelData (
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int firstScanLine, const char*& pixelData, int& pixelDataSize)

‎src/lib/OpenEXR/ImfInputFile.h

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Original file line numberDiff line numberDiff line change
@@ -147,13 +147,25 @@ class IMF_EXPORT_TYPE InputFile : public GenericInputFile
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//
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// readPixels(s) calls readPixels(s,s).
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//
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// The readPixels flavors that are passed a `FrameBuffer&` are
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// thread-safe when called at the same time as other threads make
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// calls to readPixels(fb,...). The reading functions that rely
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// on saved state from a prior call to setFrameBuffer() are NOT
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// safe to call when multiple threads are using the same InputFile.
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//
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//---------------------------------------------------------------
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IMF_EXPORT
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void readPixels (int scanLine1, int scanLine2);
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IMF_EXPORT
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void readPixels (int scanLine);
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IMF_EXPORT
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void readPixels (const FrameBuffer& frameBuffer, int scanLine1, int scanLine2);
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IMF_EXPORT
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void readPixels (const FrameBuffer& frameBuffer, int scanLine);
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//----------------------------------------------
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// Read a block of raw pixel data from the file,
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// without uncompressing it (this function is

‎src/lib/OpenEXR/ImfInputPart.h

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Original file line numberDiff line numberDiff line change
@@ -41,6 +41,10 @@ class IMF_EXPORT_TYPE InputPart
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IMF_EXPORT
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void readPixels (int scanLine);
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IMF_EXPORT
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void readPixels (const FrameBuffer& frameBuffer, int scanLine1, int scanLine2);
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IMF_EXPORT
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void readPixels (const FrameBuffer& frameBuffer, int scanLine);
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IMF_EXPORT
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void rawPixelData (
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int firstScanLine, const char*& pixelData, int& pixelDataSize);
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‎src/lib/OpenEXR/ImfScanLineInputFile.cpp

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Original file line numberDiff line numberDiff line change
@@ -1748,12 +1748,31 @@ ScanLineInputFile::readPixels (int scanLine1, int scanLine2)
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}
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}
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void
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ScanLineInputFile::readPixels (const FrameBuffer& frameBuffer, int scanLine1, int scanLine2)
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{
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// FIXME: For now, this just locks, then calls setFrameBuffer() and
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// readPixels(). It would be better to implement this function to avoid
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// locking by not needing any saved framebuffer state.
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#if ILMTHREAD_THREADING_ENABLED
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std::lock_guard<std::mutex> lock (*_data);
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#endif
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setFrameBuffer(frameBuffer);
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readPixels(scanLine1, scanLine2);
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}
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void
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ScanLineInputFile::readPixels (int scanLine)
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{
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readPixels (scanLine, scanLine);
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}
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void
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ScanLineInputFile::readPixels (const FrameBuffer& frameBuffer, int scanLine)
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{
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readPixels (frameBuffer, scanLine, scanLine);
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}
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void
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ScanLineInputFile::rawPixelData (
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int firstScanLine, const char*& pixelData, int& pixelDataSize)

‎src/lib/OpenEXR/ImfScanLineInputFile.h

Lines changed: 11 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -136,13 +136,24 @@ class IMF_EXPORT_TYPE ScanLineInputFile : public GenericInputFile
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// If threading is enabled, readPixels (s1, s2) tries to perform
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// decopmression of multiple scanlines in parallel.
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//
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// The readPixels flavors that are passed a `FrameBuffer&` are
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// thread-safe when called at the same time as other threads make
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// calls to readPixels(fb,...). The reading functions that rely
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// on saved state from a prior call to setFrameBuffer() are NOT
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// safe to call when multiple threads are using the same InputFile.
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//
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//---------------------------------------------------------------
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IMF_EXPORT
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void readPixels (int scanLine1, int scanLine2);
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IMF_EXPORT
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void readPixels (int scanLine);
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IMF_EXPORT
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void readPixels (const FrameBuffer& frameBuffer, int scanLine1, int scanLine2);
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IMF_EXPORT
155+
void readPixels (const FrameBuffer& frameBuffer, int scanLine);
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//----------------------------------------------
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// Read a block of raw pixel data from the file,
148159
// without uncompressing it (this function is

‎src/lib/OpenEXR/ImfTiledInputFile.h

Lines changed: 31 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -317,6 +317,13 @@ class IMF_EXPORT_TYPE TiledInputFile : public GenericInputFile
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// Attempting to access a tile that is not present in the file
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// throws an InputExc exception.
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//
320+
// The readTile/readTiles flavors that are passed a `FrameBuffer&`
321+
// are thread-safe when called at the same time as other threads
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// make calls to readTiles(fb,...). The reading functions that
323+
// rely on saved state from a prior call to setFrameBuffer() are
324+
// NOT safe to call when multiple threads are using the same
325+
// TiledInputFile.
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//
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//------------------------------------------------------------
321328

322329
IMF_EXPORT
@@ -326,10 +333,33 @@ class IMF_EXPORT_TYPE TiledInputFile : public GenericInputFile
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327334
IMF_EXPORT
328335
void readTiles (int dx1, int dx2, int dy1, int dy2, int lx, int ly);
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IMF_EXPORT
331337
void readTiles (int dx1, int dx2, int dy1, int dy2, int l = 0);
332338

339+
IMF_EXPORT
340+
void readTile (const FrameBuffer& frameBuffer, int dx, int dy, int l = 0);
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IMF_EXPORT
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void
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readTile (const FrameBuffer& frameBuffer, int dx, int dy, int lx, int ly);
344+
345+
IMF_EXPORT
346+
void readTiles (
347+
const FrameBuffer& frameBuffer,
348+
int dx1,
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int dx2,
350+
int dy1,
351+
int dy2,
352+
int lx,
353+
int ly);
354+
IMF_EXPORT
355+
void readTiles (
356+
const FrameBuffer& frameBuffer,
357+
int dx1,
358+
int dx2,
359+
int dy1,
360+
int dy2,
361+
int l = 0);
362+
333363
//--------------------------------------------------
334364
// Read a tile of raw pixel data from the file,
335365
// without uncompressing it (this function is

‎src/lib/OpenEXR/ImfTiledInputPart.h

Lines changed: 22 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -79,6 +79,28 @@ class IMF_EXPORT_TYPE TiledInputPart
7979
IMF_EXPORT
8080
void readTiles (int dx1, int dx2, int dy1, int dy2, int l = 0);
8181
IMF_EXPORT
82+
void readTile (const FrameBuffer& frameBuffer, int dx, int dy, int l = 0);
83+
IMF_EXPORT
84+
void
85+
readTile (const FrameBuffer& frameBuffer, int dx, int dy, int lx, int ly);
86+
IMF_EXPORT
87+
void readTiles (
88+
const FrameBuffer& frameBuffer,
89+
int dx1,
90+
int dx2,
91+
int dy1,
92+
int dy2,
93+
int lx,
94+
int ly);
95+
IMF_EXPORT
96+
void readTiles (
97+
const FrameBuffer& frameBuffer,
98+
int dx1,
99+
int dx2,
100+
int dy1,
101+
int dy2,
102+
int l = 0);
103+
IMF_EXPORT
82104
void rawTileData (
83105
int& dx,
84106
int& dy,

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