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Pa_Initialize(): Guard against recursive calls. #794

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merged 6 commits into from
Apr 4, 2023
Merged

Pa_Initialize(): Guard against recursive calls. #794

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e03753c
Pa_Initalze(): Guard against recursive calls.
daschuer Mar 14, 2023
a897650
Add a debug statement when re-enter Pa_Initalize()
daschuer Mar 15, 2023
079943e
Add link to issue fixed by the previous commits
daschuer Mar 15, 2023
9885ecc
Don't use C99 stdbool.h
daschuer Mar 15, 2023
9995043
Use new error code paCanNotInitializeRecursively
daschuer Mar 28, 2023
8faf0f6
Fix error text for paCanNotInitializeRecursively
RossBencina Mar 31, 2023
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3 changes: 2 additions & 1 deletion include/portaudio.h
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Original file line number Diff line number Diff line change
Expand Up @@ -151,7 +151,8 @@ typedef enum PaErrorCode
paCanNotReadFromAnOutputOnlyStream,
paCanNotWriteToAnInputOnlyStream,
paIncompatibleStreamHostApi,
paBadBufferPtr
paBadBufferPtr,
paCanNotInitializeRecursively
} PaErrorCode;


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17 changes: 17 additions & 0 deletions src/common/pa_front.c
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Expand Up @@ -154,6 +154,7 @@ static PaUtilHostApiRepresentation **hostApis_ = 0;
static int hostApisCount_ = 0;
static int defaultHostApiIndex_ = 0;
static int initializationCount_ = 0;
static int initializing_ = 0;
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Should this be marked volatile to prevent the compiler from doing threading unsafe optimizations here?

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My original version had this volatile due to the assumption that this will prevent the compiler form reordering.
However this assumption is not guaranteed and fortunately also not necessary, because the compiler cannot move code across external function calls like InitializeHostApis() in our case.

Another aspect is thread safety. The volatile keyword can be part of the solution but, we need also atomic test_and_set() which is not available in C89. Since thread safety is not a requirement here and also not build in any other call the using code is responsible anyway and it is no point in this PR.

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I think that initialization and shutdown are rare enough that using a mutex here to ensure thread safety would be okay. @RossBencina What do you say?

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A mutex will create a deadlock in the recursive case.
IMHO this PR is good enough, protecting Portaudio in concurrent situation is not required for the original problem.

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This is a good discussion of thread safety. But currently PortAudio is not thread safe. This fix prevents a crash caused by a stack overflow. It does not solve the thread safety issue but it is a step in the right direction. We can consider full thread safety in a later PR.

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I think that initialization and shutdown are rare enough that using a mutex here to ensure thread safety would be okay.

This is a reasonable point. However, PortAudio is a single threaded API, and this patch is intended to prevent recursion on a single thread. According to our API semantics Pa_Initialize() may not be called concurrently on two threads, and even our initializationCount_ mechanism is not thread-safe. Furthermore, we currently have no portable mutex infrastructure so adding a mutex here is a non-trivial change.

So my vote would be to merge this as-is and worry about whether initialize/terminate, or indeed the whole API, should be made thread-safe as a separate issue.

static int deviceCount_ = 0;

PaUtilStreamRepresentation *firstOpenStream_ = NULL;
Expand Down Expand Up @@ -360,8 +361,21 @@ PaError Pa_Initialize( void )
++initializationCount_;
result = paNoError;
}
else if( initializing_ )
{
// a concurrent initialization is already running
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PA_DEBUG(("Attempting to re-enter Pa_Initialize(), aborting!\n"));
result = paCanNotInitializeRecursively;
}
else
{
// set initializing_ here to
// let recursive calls execute the if branch above.
// This can happen if a driver like FlexAsio itself uses portaudio
// and avoids a stack overflow in the user application.
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// https://github.com/PortAudio/portaudio/issues/766
initializing_ = 1;

PA_VALIDATE_TYPE_SIZES;
PA_VALIDATE_ENDIANNESS;

Expand All @@ -371,6 +385,8 @@ PaError Pa_Initialize( void )
result = InitializeHostApis();
if( result == paNoError )
++initializationCount_;

initializing_ = 0;
}

PA_LOGAPI_EXIT_PAERROR( "Pa_Initialize", result );
Expand Down Expand Up @@ -453,6 +469,7 @@ const char *Pa_GetErrorText( PaError errorCode )
case paCanNotWriteToAnInputOnlyStream: result = "Can't write to an input only stream"; break;
case paIncompatibleStreamHostApi: result = "Incompatible stream host API"; break;
case paBadBufferPtr: result = "Bad buffer pointer"; break;
case paCanNotInitializeRecursively: result = "PortAudio can not initialized recursively"; break;
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default:
if( errorCode > 0 )
result = "Invalid error code (value greater than zero)";
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