fix(#30): one concurrent thread by default

README.md

@@ -60,7 +60,7 @@ Here you can see some performance test comparisons for multiple scenarios:
 
 #### Benchmarks
 
-Tested using Go 1.4 and libvips-7.42.3 in OSX i7 2.7Ghz
+Tested using Go 1.4.2 and libvips-7.42.3 in OSX i7 2.7Ghz
 ```
 BenchmarkResizeLargeJpeg  50    43400480 ns/op
 BenchmarkResizePng        20    57592174 ns/op
@@ -237,6 +237,11 @@ Run the process passing the `DEBUG` environment variable
 DEBUG=* ./app 
 ```
 
+Enable libvips traces (note that a lot of data will be written in stdout):
+```
+VIPS_TRACE=1 ./app 
+```
+
 #### func  DetermineImageTypeName
 
 ```go

vips.go

@@ -9,6 +9,7 @@ import "C"
 
 import (
 	"errors"
+	"os"
 	"runtime"
 	"strings"
 	"sync"
@@ -68,9 +69,19 @@ func Initialize() {
 		panic("unable to start vips!")
 	}
 
-	C.vips_concurrency_set(0)                   // default
+	C.vips_cache_set_max_mem(100 * 1024 * 1024)
-	C.vips_cache_set_max_mem(100 * 1024 * 1024) // 100 MB
+	C.vips_cache_set_max(500)
-	C.vips_cache_set_max(500)                   // 500 operations
+
+	// Explicit concurrency limit to avoid thread-unsafe issues.
+	// See: https://github.com/jcupitt/libvips/issues/261#issuecomment-92850414
+	if os.Getenv("VIPS_CONCURRENCY") == "" {
+		C.vips_concurrency_set(1)
+	}
+
+	if os.Getenv("VIPS_TRACE") != "" {
+		C.vips_enable_cache_set_trace()
+	}
+
 	initialized = true
 }
 
@@ -113,7 +124,9 @@ func vipsHasProfile(image *C.struct__VipsImage) bool {
 }
 
 func vipsWindowSize(name string) float64 {
-	return float64(C.interpolator_window_size(C.CString(name)))
+	cname := C.CString(name)
+	defer C.free(unsafe.Pointer(cname))
+	return float64(C.interpolator_window_size(cname))
 }
 
 func vipsSpace(image *C.struct__VipsImage) string {
@@ -175,7 +188,7 @@ func vipsWatermark(image *C.struct__VipsImage, w Watermark) (*C.struct__VipsImag
 	defer C.free(unsafe.Pointer(text))
 	defer C.free(unsafe.Pointer(font))
 
-	err := C.vips_watermark(image, &out, (*C.watermarkTextOptions)(unsafe.Pointer(&textOpts)), (*C.watermarkOptions)(unsafe.Pointer(&opts)))
+	err := C.vips_watermark(image, &out, (*C.WatermarkTextOptions)(unsafe.Pointer(&textOpts)), (*C.WatermarkOptions)(unsafe.Pointer(&opts)))
 	if err != 0 {
 		return nil, catchVipsError()
 	}

vips.h

@@ -14,7 +14,7 @@ enum types {
 typedef struct {
 	const char *Text;
 	const char *Font;
-} watermarkTextOptions;
+} WatermarkTextOptions;
 
 typedef struct {
 	int    Width;
@@ -23,7 +23,7 @@ typedef struct {
 	int    NoReplicate;
 	float  Opacity;
 	double Background[3];
-} watermarkOptions;
+} WatermarkOptions;
 
 int
 vips_affine_interpolator(VipsImage *in, VipsImage **out, double a, double b, double c, double d, VipsInterpolate *interpolator)
@@ -187,7 +187,7 @@ vips_watermark_replicate(VipsImage *orig, VipsImage *in, VipsImage **out)
 };
 
 int
-vips_watermark(VipsImage *in, VipsImage **out, watermarkTextOptions *to, watermarkOptions *o)
+vips_watermark(VipsImage *in, VipsImage **out, WatermarkTextOptions *to, WatermarkOptions *o)
 {
 	double ones[3] = { 1, 1, 1 };
 
@@ -244,3 +244,8 @@ vips_watermark(VipsImage *in, VipsImage **out, watermarkTextOptions *to, waterma
 	return 0;
 };
 
+void
+vips_enable_cache_set_trace()
+{
+	vips_cache_set_trace(TRUE);
+};