Add API parameter to cap thread usage

examples/zarrv2-compressed-s3.c

@@ -27,7 +27,8 @@ int main() {
         .s3_settings = &s3,
         .compression_settings = &compression,
         .data_type = ZarrDataType_int32,
-        .version = ZarrVersion_2
+        .version = ZarrVersion_2,
+        .max_threads = 0, // use all available threads
     };
 
     // Set up dimensions (t, c, y, x)

examples/zarrv2-raw-filesystem.c

@@ -11,7 +11,8 @@ int main() {
         .s3_settings = NULL,
         .compression_settings = NULL,
         .data_type = ZarrDataType_int32,
-        .version = ZarrVersion_2
+        .version = ZarrVersion_2,
+        .max_threads = 0, // use all available threads
     };
 
     // Set up dimensions (t, y, x)

examples/zarrv3-compressed-filesystem.c

@@ -24,6 +24,7 @@ main()
         .compression_settings = &compression,
         .data_type = ZarrDataType_uint16,
         .version = ZarrVersion_3,
+        .max_threads = 0, // use all available threads
     };
 
     // Set up dimensions (t, y, x)

examples/zarrv3-compressed-multiscale-s3.c

@@ -34,6 +34,7 @@ main()
         .data_type = ZarrDataType_uint16,
         .version = ZarrVersion_3,
         .multiscale = true,
+        .max_threads = 0, // use all available threads
     };
 
     // Set up dimensions (t, z, y, x)

examples/zarrv3-compressed-s3.c

@@ -32,6 +32,7 @@ main()
         .compression_settings = &compression,
         .data_type = ZarrDataType_uint16,
         .version = ZarrVersion_3,
+        .max_threads = 0, // use all available threads
     };
 
     // Set up dimensions (t, y, x)

examples/zarrv3-raw-filesystem.c

@@ -16,6 +16,7 @@ main()
         .compression_settings = NULL,
         .data_type = ZarrDataType_uint16,
         .version = ZarrVersion_3,
+        .max_threads = 0, // use all available threads
     };
 
     // Set up dimensions (t, y, x)

examples/zarrv3-raw-multiscale-filesystem.c

@@ -17,6 +17,7 @@ main()
         .multiscale = true,
         .data_type = ZarrDataType_uint16,
         .version = ZarrVersion_3,
+        .max_threads = 0, // use all available threads
     };
 
     // Set up 5D array (t, c, z, y, x)

examples/zarrv3-raw-s3.c

@@ -19,7 +19,8 @@ int main() {
         .s3_settings = &s3,
         .compression_settings = NULL,  // No compression
         .data_type = ZarrDataType_uint16,
-        .version = ZarrVersion_3
+        .version = ZarrVersion_3,
+        .max_threads = 0, // use all available threads
     };
 
     // Set up dimensions (t, z, y, x)

include/acquire.zarr.h

@@ -33,6 +33,7 @@ extern "C"
         bool multiscale; /**< Whether to stream to multiple levels of detail. */
         ZarrDataType data_type; /**< The pixel data type of the dataset. */
         ZarrVersion version; /**< The version of the Zarr format to use. 2 or 3. */
+        unsigned int max_threads; /**< The maximum number of threads to use in the stream. Set to 0 to use the supported number of concurrent threads. */
     } ZarrStreamSettings;
 
     typedef struct ZarrStream_s ZarrStream;

pyproject.toml

@@ -10,8 +10,8 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "acquire-zarr"
-version = "0.0.5"
-description = "Python bindings for acquire-zarr"
+version = "0.1.0"
+description = "Performant streaming to Zarr storage, on filesystem or cloud"
 authors = [
     {name = "Alan Liddell", email = "[email protected]"}
 ]

python/acquire-zarr-py.cpp

@@ -274,6 +274,12 @@ class PyZarrStreamSettings
     ZarrVersion version() const { return version_; }
     void set_version(ZarrVersion version) { version_ = version; }
 
+    unsigned int max_threads() const { return max_threads_; }
+    void set_max_threads(unsigned int max_threads)
+    {
+        max_threads_ = max_threads;
+    }
+
   private:
     std::string store_path_;
     std::optional<std::string> custom_metadata_{ std::nullopt };
@@ -284,6 +290,7 @@ class PyZarrStreamSettings
     bool multiscale_ = false;
     ZarrDataType data_type_{ ZarrDataType_uint8 };
     ZarrVersion version_{ ZarrVersion_2 };
+    unsigned int max_threads_{ std::thread::hardware_concurrency() };
 };
 
 class PyZarrStream
@@ -304,6 +311,7 @@ class PyZarrStream
             .multiscale = settings.multiscale(),
             .data_type = settings.data_type(),
             .version = settings.version(),
+            .max_threads = settings.max_threads(),
         };
 
         store_path_ = settings.store_path();
@@ -632,6 +640,7 @@ PYBIND11_MODULE(acquire_zarr, m)
                  std::string(data_type_to_str(self.data_type())) +
                  ", version=ZarrVersion." +
                  std::string(self.version() == ZarrVersion_2 ? "V2" : "V3") +
+                 ", max_threads=" + std::to_string(self.max_threads()) +
                  ")";
                return repr;
            })
@@ -692,7 +701,10 @@ PYBIND11_MODULE(acquire_zarr, m)
                     &PyZarrStreamSettings::set_data_type)
       .def_property("version",
                     &PyZarrStreamSettings::version,
-                    &PyZarrStreamSettings::set_version);
+                    &PyZarrStreamSettings::set_version)
+      .def_property("max_threads",
+                    &PyZarrStreamSettings::max_threads,
+                    &PyZarrStreamSettings::set_max_threads);
 
     py::class_<PyZarrStream>(m, "ZarrStream")
       .def(py::init<PyZarrStreamSettings>())

python/acquire_zarr.pyi

@@ -354,6 +354,7 @@ class StreamSettings:
     s3: Optional[S3Settings]
     store_path: str
     version: ZarrVersion
+    max_threads: int
 
     def __init__(self, **kwargs) -> None:
         ...

python/tests/test_settings.py

@@ -135,3 +135,10 @@ def test_set_version(settings):
     settings.version = acquire_zarr.ZarrVersion.V3
 
     assert settings.version == acquire_zarr.ZarrVersion.V3
+
+
+def test_set_max_threads(settings):
+    assert settings.max_threads > 0 # depends on your system, but will be nonzero
+
+    settings.max_threads = 4
+    assert settings.max_threads == 4

src/streaming/zarr.stream.cpp

@@ -374,9 +374,21 @@ ZarrStream::ZarrStream_s(struct ZarrStreamSettings_s* settings)
     commit_settings_(settings);
 
     // spin up thread pool
+    unsigned int max_threads = settings->max_threads;
+    const auto hardware_concurrency = std::thread::hardware_concurrency();
+
+    if (max_threads == 0) {
+        if (hardware_concurrency > 0) {
+            LOG_DEBUG("Using ", hardware_concurrency, " threads");
+            max_threads = hardware_concurrency;
+        } else {
+            LOG_WARNING(
+              "Unable to determine hardware concurrency, using 1 thread");
+            max_threads = 1;
+        }
+    }
     thread_pool_ = std::make_shared<zarr::ThreadPool>(
-      std::thread::hardware_concurrency(),
-      [this](const std::string& err) { this->set_error_(err); });
+      max_threads, [this](const std::string& err) { this->set_error_(err); });
 
     // allocate a frame buffer
     frame_buffer_.resize(

tests/integration/stream-zarr-v2-compressed-to-filesystem.cpp

@@ -44,6 +44,7 @@ setup()
         .s3_settings = nullptr,
         .data_type = ZarrDataType_int32,
         .version = ZarrVersion_2,
+        .max_threads = 0, // use all available threads
     };
 
     ZarrCompressionSettings compression_settings = {

tests/integration/stream-zarr-v2-compressed-to-s3.cpp

@@ -157,6 +157,7 @@ setup()
         .store_path = TEST,
         .data_type = ZarrDataType_int32,
         .version = ZarrVersion_2,
+        .max_threads = 0, // use all available threads
     };
 
     ZarrS3Settings s3_settings{

tests/integration/stream-zarr-v2-raw-to-filesystem.cpp

@@ -45,6 +45,7 @@ setup()
         .compression_settings = nullptr,
         .data_type = ZarrDataType_int32,
         .version = ZarrVersion_2,
+        .max_threads = 0, // use all available threads
     };
 
     CHECK_OK(ZarrStreamSettings_create_dimension_array(&settings, 5));

tests/integration/stream-zarr-v2-raw-to-s3.cpp

@@ -158,6 +158,7 @@ setup()
         .compression_settings = nullptr,
         .data_type = ZarrDataType_int32,
         .version = ZarrVersion_2,
+        .max_threads = 0, // use all available threads
     };
 
     ZarrS3Settings s3_settings{

tests/integration/stream-zarr-v3-compressed-to-filesystem.cpp

@@ -60,6 +60,7 @@ setup()
         .s3_settings = nullptr,
         .data_type = ZarrDataType_uint16,
         .version = ZarrVersion_3,
+        .max_threads = 0, // use all available threads
     };
 
     ZarrCompressionSettings compression_settings = {

tests/integration/stream-zarr-v3-compressed-to-s3.cpp

@@ -172,6 +172,7 @@ setup()
         .store_path = TEST,
         .data_type = ZarrDataType_uint16,
         .version = ZarrVersion_3,
+        .max_threads = 0, // use all available threads
     };
 
     ZarrS3Settings s3_settings{

tests/integration/stream-zarr-v3-raw-to-filesystem.cpp

@@ -61,6 +61,7 @@ setup()
         .compression_settings = nullptr,
         .data_type = ZarrDataType_uint16,
         .version = ZarrVersion_3,
+        .max_threads = 0, // use all available threads
     };
 
     CHECK_OK(ZarrStreamSettings_create_dimension_array(&settings, 5));

tests/integration/stream-zarr-v3-raw-to-s3.cpp

@@ -175,6 +175,7 @@ setup()
         .compression_settings = nullptr,
         .data_type = ZarrDataType_uint16,
         .version = ZarrVersion_3,
+        .max_threads = 0, // use all available threads
     };
 
     ZarrS3Settings s3_settings{

tests/unit-tests/create-stream.cpp

@@ -45,6 +45,7 @@ main()
     ZarrStreamSettings settings;
     memset(&settings, 0, sizeof(settings));
     settings.version = ZarrVersion_2;
+    settings.max_threads = std::thread::hardware_concurrency();
 
     try {
         // try to create a stream with no store path