Merge pull request #2947 from PaulBoersma/master

parallel threads have unique IDs, for error handling

Author: PaulBoersma

melder/MelderThread.cpp

@@ -16,14 +16,22 @@
  * along with this work. If not, see <http://www.gnu.org/licenses/>.
  */
 
-#include "MelderThread.h"
+#include "melder.h"
 
 integer MelderThread_getNumberOfProcessors () {
 	//return 1;   // un-comment-out to force single-threading
 	return Melder_clippedLeft (1_integer, uinteger_to_integer_a (std::thread::hardware_concurrency ()));
 }
 
-/* global */ std::thread::id theMelder_error_threadId;
+/* global */ std::atomic <integer> theMelder_error_threadId;
+
+integer Melder_thisThread_getUniqueID () {
+	static std::atomic <integer> uniqueID = 0;
+	static thread_local integer thisThread_uniqueID = uniqueID ++;
+	//TRACE
+	trace (thisThread_uniqueID);
+	return thisThread_uniqueID;
+}
 
 integer MelderThread_computeNumberOfThreads (
 	const integer numberOfElements,
@@ -90,7 +98,7 @@ void MelderThread_run (
 			spawns [ispawn0]. join ();
 	}
 	if (*p_errorFlag) {
-		theMelder_error_threadId = std::this_thread::get_id ();   // TODO: make this truly unique
+		theMelder_error_threadId = Melder_thisThread_getUniqueID ();
 		throw MelderError();   // turn the error flag back into a MelderError
 	}
 }

melder/MelderThread.h

@@ -30,6 +30,16 @@ integer MelderThread_computeNumberOfThreads (
 	bool useRandom
 );
 
+/*
+	The following is a replacement for std::this_thread::get_id(),
+	which is not guaranteeed to return a unique ID.
+
+	A case where this matters is if a throwing thread has finished,
+	and then a new thread is created with the same idea and quickly throws as well.
+	Admittedly, this is rare, but it is not impossible and it is easy to prevent it.
+*/
+integer Melder_thisThread_getUniqueID ();
+
 #define MelderThread_TRY  \
 	try {
 

melder/melder.h

@@ -33,7 +33,7 @@
 #include <new>   // placement new
 #include <algorithm>   // std::min
 #include <limits>   // std::numeric_limits<double>::max(), std::numeric_limits<double>::lowest()
-#include <thread>
+#include <atomic>   // std::atomic<integer>
 
 /*
 	Law of Demeter for class functions defined outside class definition.
@@ -83,6 +83,7 @@
 
 #include "MelderArg.h"   // MelderArg (requires Melder_double, MelderFile, Melder_VEC)
 #include "MelderString.h"   // MelderString_append (requires MelderArg)
+#include "MelderThread.h"   // Melder_thisThread_getUniqueID
 #include "melder_textencoding.h"   // Melder_length_utf8, Melder_32to8 (requires MelderString)
 #include "melder_debug.h"   // trace (requires MelderFile, MelderArg, MelderString), Melder_debug
 #include "MelderFile.h"   // MelderFile_open (requires MelderFile), MelderFile_write (requires MelderArg)

melder/melder_error.cpp

@@ -93,6 +93,13 @@ conststring32 Melder_getError () {
 }
 
 void Melder_appendError_noLine (const MelderArg& arg) {
+	std::lock_guard lock (theMelder_error_mutex);
+	if (Melder_hasError ()) {
+		if (Melder_thisThread_getUniqueID () != theMelder_error_threadId)
+			return;
+	} else {
+		theMelder_error_threadId = Melder_thisThread_getUniqueID ();
+	}
 	MelderError::_append (arg._arg);
 }
 

melder/melder_error.h

@@ -23,7 +23,7 @@ class MelderError {
 	static void _append (conststring32 message);
 };
 extern std::mutex theMelder_error_mutex;
-extern std::thread::id theMelder_error_threadId;
+extern std::atomic <integer> theMelder_error_threadId;
 
 bool Melder_hasError ();
 bool Melder_hasError (conststring32 partialError);
@@ -70,10 +70,10 @@ template <typename... Args>
 void Melder_appendError (const MelderArg& first, Args... rest) {
 	std::lock_guard lock (theMelder_error_mutex);
 	if (Melder_hasError ()) {
-		if (std::this_thread::get_id () != theMelder_error_threadId)
+		if (Melder_thisThread_getUniqueID () != theMelder_error_threadId)
 			return;
 	} else {
-		theMelder_error_threadId = std::this_thread::get_id ();
+		theMelder_error_threadId = Melder_thisThread_getUniqueID ();
 	}
 	_recursiveTemplate_Melder_appendError (first, rest...);
 	MelderError::_append (U"\n");